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Mike Christie

2022-Feb-02 21:01 UTC

[PATCH 0/8] Use copy_process in vhost layer

The following patches made over Linus's tree, allow the vhost layer to do
a copy_process on the thread that does the VHOST_SET_OWNER ioctl like how
io_uring does a copy_process against its userspace app. This allows the
vhost layer's worker threads to inherit cgroups, namespaces, address
space, etc and this worker thread will also be accounted for against that
owner/parent process's RLIMIT_NPROC limit.

If you are not familiar with qemu and vhost here is more detailed
problem description:

Qemu will create vhost devices in the kernel which perform network, SCSI,
etc IO and management operations from worker threads created by the
kthread API. Because the kthread API does a copy_process on the kthreadd
thread, the vhost layer has to use kthread_use_mm to access the Qemu
thread's memory and cgroup_attach_task_all to add itself to the Qemu
thread's cgroups.

The problem with this approach is that we then have to add new functions/
args/functionality for every thing we want to inherit. I started doing
that here:

https://lkml.org/lkml/2021/6/23/1233

for the RLIMIT_NPROC check, but it seems it might be easier to just
inherit everything from the beginning, becuase I'd need to do something
like that patch several times.

V7:
- Drop generic user_worker_* helpers and replace with vhost_task specific
  ones.
- Drop autoreap patch. Use kernel_wait4 instead.
- Fix issue where vhost.ko could be removed while the worker function is
  still running.
V6:
- Rename kernel_worker to user_worker and fix prefixes.
- Add better patch descriptions.
V5:
- Handle kbuild errors by building patchset against current kernel that
  has all deps merged. Also add patch to remove create_io_thread code as
  it's not used anymore.
- Rebase patchset against current kernel and handle a new vm PF_IO_WORKER
  case added in 5.16-rc1.
- Add PF_USER_WORKER flag so we can check it later after the initial
  thread creation for the wake up, vm and singal cses.
- Added patch to auto reap the worker thread.
V4:
- Drop NO_SIG patch and replaced with Christian's SIG_IGN patch.
- Merged Christian's kernel_worker_flags_valid helpers into patch 5 that
  added the new kernel worker functions.
- Fixed extra "i" issue.
- Added PF_USER_WORKER flag and added check that kernel_worker_start users
  had that flag set. Also dropped patches that passed worker flags to
  copy_thread and replaced with PF_USER_WORKER check.
V3:
- Add parentheses in p->flag and work_flags check in copy_thread.
- Fix check in arm/arm64 which was doing the reverse of other archs
  where it did likely(!flags) instead of unlikely(flags).
V2:
- Rename kernel_copy_process to kernel_worker.
- Instead of exporting functions, make kernel_worker() a proper
  function/API that does common work for the caller.
- Instead of adding new fields to kernel_clone_args for each option
  make it flag based similar to CLONE_*.
- Drop unused completion struct in vhost.
- Fix compile warnings by merging vhost cgroup cleanup patch and
  vhost conversion patch.

Mike Christie

2022-Feb-02 21:01 UTC

head link

[PATCH 1/8] fork: Make IO worker options flag based

This patchset adds a couple new options to kernel_clone_args for the vhost
layer which is going to work like PF_IO_WORKER but will differ enough that
we will need to add several fields to kernel_clone_args. This patch moves
us to a flags based approach for these types of users.

Signed-off-by: Mike Christie <michael.christie at oracle.com>
Suggested-by: Christian Brauner <christian.brauner at ubuntu.com>
Acked-by: Christian Brauner <christian.brauner at ubuntu.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
---
 include/linux/sched/task.h | 4 +++-
 kernel/fork.c              | 4 ++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index b9198a1b3a84..0bf95966ae7d 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -18,8 +18,11 @@ struct css_set;
 /* All the bits taken by the old clone syscall. */
 #define CLONE_LEGACY_FLAGS 0xffffffffULL
 
+#define USER_WORKER_IO		BIT(0)
+
 struct kernel_clone_args {
 	u64 flags;
+	u32 worker_flags;
 	int __user *pidfd;
 	int __user *child_tid;
 	int __user *parent_tid;
@@ -31,7 +34,6 @@ struct kernel_clone_args {
 	/* Number of elements in *set_tid */
 	size_t set_tid_size;
 	int cgroup;
-	int io_thread;
 	struct cgroup *cgrp;
 	struct css_set *cset;
 };
diff --git a/kernel/fork.c b/kernel/fork.c
index d75a528f7b21..9273fd81a329 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1998,7 +1998,7 @@ static __latent_entropy struct task_struct *copy_process(
 	p = dup_task_struct(current, node);
 	if (!p)
 		goto fork_out;
-	if (args->io_thread) {
+	if (args->worker_flags & USER_WORKER_IO) {
 		/*
 		 * Mark us an IO worker, and block any signal that isn't
 		 * fatal or STOP
@@ -2497,7 +2497,7 @@ struct task_struct *create_io_thread(int (*fn)(void *),
void *arg, int node)
 		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
 		.stack		= (unsigned long)fn,
 		.stack_size	= (unsigned long)arg,
-		.io_thread	= 1,
+		.worker_flags	= USER_WORKER_IO,
 	};
 
 	return copy_process(NULL, 0, node, &args);
-- 
2.25.1

Mike Christie

2022-Feb-02 21:01 UTC

head link

[PATCH 2/8] fork/vm: Move common PF_IO_WORKER behavior to new flag

This adds a new flag, PF_USER_WORKER, that's used for behavior common to
to both PF_IO_WORKER and users like vhost which will use a new helper
instead of create_io_thread because they require different behavior.

The common behavior PF_USER_WORKER covers is the initial frame and fpu
setup and the vm reclaim handling.

Signed-off-by: Mike Christie <michael.christie at oracle.com>
[For m68k changes]
Acked-by: Geert Uytterhoeven <geert at linux-m68k.org>
---
 arch/alpha/kernel/process.c      | 2 +-
 arch/arc/kernel/process.c        | 2 +-
 arch/arm/kernel/process.c        | 2 +-
 arch/arm64/kernel/process.c      | 2 +-
 arch/csky/kernel/process.c       | 2 +-
 arch/h8300/kernel/process.c      | 2 +-
 arch/hexagon/kernel/process.c    | 2 +-
 arch/ia64/kernel/process.c       | 2 +-
 arch/m68k/kernel/process.c       | 2 +-
 arch/microblaze/kernel/process.c | 2 +-
 arch/mips/kernel/process.c       | 2 +-
 arch/nds32/kernel/process.c      | 2 +-
 arch/nios2/kernel/process.c      | 2 +-
 arch/openrisc/kernel/process.c   | 2 +-
 arch/parisc/kernel/process.c     | 2 +-
 arch/powerpc/kernel/process.c    | 2 +-
 arch/riscv/kernel/process.c      | 2 +-
 arch/s390/kernel/process.c       | 2 +-
 arch/sh/kernel/process_32.c      | 2 +-
 arch/sparc/kernel/process_32.c   | 2 +-
 arch/sparc/kernel/process_64.c   | 2 +-
 arch/um/kernel/process.c         | 2 +-
 arch/x86/kernel/fpu/core.c       | 4 ++--
 arch/x86/kernel/process.c        | 2 +-
 arch/xtensa/kernel/process.c     | 2 +-
 include/linux/sched.h            | 1 +
 include/linux/sched/task.h       | 3 ++-
 kernel/fork.c                    | 6 +++++-
 mm/vmscan.c                      | 4 ++--
 29 files changed, 36 insertions(+), 30 deletions(-)

diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index 5f8527081da9..f4759e4ee4a9 100644
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -249,7 +249,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp,
 	childti->pcb.ksp = (unsigned long) childstack;
 	childti->pcb.flags = 1;	/* set FEN, clear everything else */
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		/* kernel thread */
 		memset(childstack, 0,
 			sizeof(struct switch_stack) + sizeof(struct pt_regs));
diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index 8e90052f6f05..b409ecb1407f 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -191,7 +191,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp,
 	childksp[0] = 0;			/* fp */
 	childksp[1] = (unsigned long)ret_from_fork; /* blink */
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(c_regs, 0, sizeof(struct pt_regs));
 
 		c_callee->r13 = kthread_arg;
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index d47159f3791c..44603062d661 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -251,7 +251,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
stack_start,
 	thread->cpu_domain = get_domain();
 #endif
 
-	if (likely(!(p->flags & (PF_KTHREAD | PF_IO_WORKER)))) {
+	if (likely(!(p->flags & (PF_KTHREAD | PF_USER_WORKER)))) {
 		*childregs = *current_pt_regs();
 		childregs->ARM_r0 = 0;
 		if (stack_start)
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 5369e649fa79..2528fb9650ef 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -334,7 +334,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
stack_start,
 
 	ptrauth_thread_init_kernel(p);
 
-	if (likely(!(p->flags & (PF_KTHREAD | PF_IO_WORKER)))) {
+	if (likely(!(p->flags & (PF_KTHREAD | PF_USER_WORKER)))) {
 		*childregs = *current_pt_regs();
 		childregs->regs[0] = 0;
 
diff --git a/arch/csky/kernel/process.c b/arch/csky/kernel/process.c
index 3d0ca22cd0e2..509f2bfe4ace 100644
--- a/arch/csky/kernel/process.c
+++ b/arch/csky/kernel/process.c
@@ -49,7 +49,7 @@ int copy_thread(unsigned long clone_flags,
 	/* setup thread.sp for switch_to !!! */
 	p->thread.sp = (unsigned long)childstack;
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childstack->r15 = (unsigned long) ret_from_kernel_thread;
 		childstack->r10 = kthread_arg;
diff --git a/arch/h8300/kernel/process.c b/arch/h8300/kernel/process.c
index 8833fa4f5d51..050aca44ba6d 100644
--- a/arch/h8300/kernel/process.c
+++ b/arch/h8300/kernel/process.c
@@ -112,7 +112,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp,
 
 	childregs = (struct pt_regs *) (THREAD_SIZE + task_stack_page(p)) - 1;
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->retpc = (unsigned long) ret_from_kernel_thread;
 		childregs->er4 = topstk; /* arg */
diff --git a/arch/hexagon/kernel/process.c b/arch/hexagon/kernel/process.c
index 232dfd8956aa..40f8294c6c7c 100644
--- a/arch/hexagon/kernel/process.c
+++ b/arch/hexagon/kernel/process.c
@@ -73,7 +73,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
unsigned long arg,
 						    sizeof(*ss));
 	ss->lr = (unsigned long)ret_from_fork;
 	p->thread.switch_sp = ss;
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(childregs, 0, sizeof(struct pt_regs));
 		/* r24 <- fn, r25 <- arg */
 		ss->r24 = usp;
diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c
index 834df24a88f1..29015ebdcf1d 100644
--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -338,7 +338,7 @@ copy_thread(unsigned long clone_flags, unsigned long
user_stack_base,
 
 	ia64_drop_fpu(p);	/* don't pick up stale state from a CPU's fph */
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		if (unlikely(!user_stack_base)) {
 			/* fork_idle() called us */
 			return 0;
diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c
index a6030dbaa089..cbb693012b5e 100644
--- a/arch/m68k/kernel/process.c
+++ b/arch/m68k/kernel/process.c
@@ -157,7 +157,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp, unsigned long arg,
 	 */
 	p->thread.fc = USER_DATA;
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		/* kernel thread */
 		memset(frame, 0, sizeof(struct fork_frame));
 		frame->regs.sr = PS_S;
diff --git a/arch/microblaze/kernel/process.c b/arch/microblaze/kernel/process.c
index 5e2b91c1e8ce..de1da9900f7e 100644
--- a/arch/microblaze/kernel/process.c
+++ b/arch/microblaze/kernel/process.c
@@ -59,7 +59,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
unsigned long arg,
 	struct pt_regs *childregs = task_pt_regs(p);
 	struct thread_info *ti = task_thread_info(p);
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		/* if we're creating a new kernel thread then just zeroing all
 		 * the registers. That's OK for a brand new thread.*/
 		memset(childregs, 0, sizeof(struct pt_regs));
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index cbff1b974f88..6f1ed337cd41 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -120,7 +120,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp,
 	/*  Put the stack after the struct pt_regs.  */
 	childksp = (unsigned long) childregs;
 	p->thread.cp0_status = (read_c0_status() & ~(ST0_CU2|ST0_CU1)) |
ST0_KERNEL_CUMASK;
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		/* kernel thread */
 		unsigned long status = p->thread.cp0_status;
 		memset(childregs, 0, sizeof(struct pt_regs));
diff --git a/arch/nds32/kernel/process.c b/arch/nds32/kernel/process.c
index 49fab9e39cbf..dba91dd1e289 100644
--- a/arch/nds32/kernel/process.c
+++ b/arch/nds32/kernel/process.c
@@ -156,7 +156,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
stack_start,
 
 	memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context));
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(childregs, 0, sizeof(struct pt_regs));
 		/* kernel thread fn */
 		p->thread.cpu_context.r6 = stack_start;
diff --git a/arch/nios2/kernel/process.c b/arch/nios2/kernel/process.c
index f8ea522a1588..eabf3452e5e2 100644
--- a/arch/nios2/kernel/process.c
+++ b/arch/nios2/kernel/process.c
@@ -109,7 +109,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp, unsigned long arg,
 	struct switch_stack *childstack  		((struct switch_stack *)childregs) - 1;
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(childstack, 0,
 			sizeof(struct switch_stack) + sizeof(struct pt_regs));
 
diff --git a/arch/openrisc/kernel/process.c b/arch/openrisc/kernel/process.c
index 3c0c91bcdcba..aa110383cfa1 100644
--- a/arch/openrisc/kernel/process.c
+++ b/arch/openrisc/kernel/process.c
@@ -172,7 +172,7 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
unsigned long arg,
 	sp -= sizeof(struct pt_regs);
 	kregs = (struct pt_regs *)sp;
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(kregs, 0, sizeof(struct pt_regs));
 		kregs->gpr[20] = usp; /* fn, kernel thread */
 		kregs->gpr[22] = arg;
diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
index ea3d83b6fb62..a76120e30eb4 100644
--- a/arch/parisc/kernel/process.c
+++ b/arch/parisc/kernel/process.c
@@ -197,7 +197,7 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
 	extern void * const ret_from_kernel_thread;
 	extern void * const child_return;
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		/* kernel thread */
 		memset(cregs, 0, sizeof(struct pt_regs));
 		if (!usp) /* idle thread */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 984813a4d5dc..02f91fcc1417 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1736,7 +1736,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp,
 	/* Copy registers */
 	sp -= sizeof(struct pt_regs);
 	childregs = (struct pt_regs *) sp;
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		/* kernel thread */
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->gpr[1] = sp + sizeof(struct pt_regs);
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 03ac3aa611f5..8deeb94eb51e 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -125,7 +125,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp, unsigned long arg,
 	struct pt_regs *childregs = task_pt_regs(p);
 
 	/* p->thread holds context to be restored by __switch_to() */
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		/* Kernel thread */
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->gp = gp_in_global;
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 71d86f73b02c..51169bb351d4 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -130,7 +130,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
new_stackp,
 	frame->sf.gprs[9] = (unsigned long)frame;
 
 	/* Store access registers to kernel stack of new process. */
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		/* kernel thread */
 		memset(&frame->childregs, 0, sizeof(struct pt_regs));
 		frame->childregs.psw.mask = PSW_KERNEL_BITS | PSW_MASK_DAT |
diff --git a/arch/sh/kernel/process_32.c b/arch/sh/kernel/process_32.c
index 1c28e3cddb60..0506a739b0a8 100644
--- a/arch/sh/kernel/process_32.c
+++ b/arch/sh/kernel/process_32.c
@@ -114,7 +114,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp, unsigned long arg,
 
 	childregs = task_pt_regs(p);
 	p->thread.sp = (unsigned long) childregs;
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(childregs, 0, sizeof(struct pt_regs));
 		p->thread.pc = (unsigned long) ret_from_kernel_thread;
 		childregs->regs[4] = arg;
diff --git a/arch/sparc/kernel/process_32.c b/arch/sparc/kernel/process_32.c
index 2dc0bf9fe62e..5386e56b5e6c 100644
--- a/arch/sparc/kernel/process_32.c
+++ b/arch/sparc/kernel/process_32.c
@@ -296,7 +296,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
unsigned long arg,
 	ti->ksp = (unsigned long) new_stack;
 	p->thread.kregs = childregs;
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		extern int nwindows;
 		unsigned long psr;
 		memset(new_stack, 0, STACKFRAME_SZ + TRACEREG_SZ);
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index f5b2cac8669f..6058b3966f71 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -594,7 +594,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
unsigned long arg,
 				       sizeof(struct sparc_stackf));
 	t->fpsaved[0] = 0;
 
-	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (unlikely(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		memset(child_trap_frame, 0, child_stack_sz);
 		__thread_flag_byte_ptr(t)[TI_FLAG_BYTE_CWP] = 
 			(current_pt_regs()->tstate + 1) & TSTATE_CWP;
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 4a420778ed87..25dd496fd820 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -158,7 +158,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 		unsigned long arg, struct task_struct * p, unsigned long tls)
 {
 	void (*handler)(void);
-	int kthread = current->flags & (PF_KTHREAD | PF_IO_WORKER);
+	int kthread = current->flags & (PF_KTHREAD | PF_USER_WORKER);
 	int ret = 0;
 
 	p->thread = (struct thread_struct) INIT_THREAD;
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 8dea01ffc5c1..c5b34fa8bb0c 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -579,10 +579,10 @@ int fpu_clone(struct task_struct *dst, unsigned long
clone_flags)
 	set_tsk_thread_flag(dst, TIF_NEED_FPU_LOAD);
 
 	/*
-	 * No FPU state inheritance for kernel threads and IO
+	 * No FPU state inheritance for kernel threads and user
 	 * worker threads.
 	 */
-	if (dst->flags & (PF_KTHREAD | PF_IO_WORKER)) {
+	if (dst->flags & (PF_KTHREAD | PF_USER_WORKER)) {
 		/* Clear out the minimal state */
 		memcpy(&dst_fpu->fpstate->regs, &init_fpstate.regs,
 		       init_fpstate_copy_size());
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 81d8ef036637..b0e58fe55b31 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -195,7 +195,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
unsigned long arg,
 	task_user_gs(p) = get_user_gs(current_pt_regs());
 #endif
 
-	if (unlikely(p->flags & PF_IO_WORKER)) {
+	if (unlikely(p->flags & PF_USER_WORKER)) {
 		/*
 		 * An IO thread is a user space thread, but it doesn't
 		 * return to ret_after_fork().
diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c
index bd80df890b1e..00d81668ead4 100644
--- a/arch/xtensa/kernel/process.c
+++ b/arch/xtensa/kernel/process.c
@@ -224,7 +224,7 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp_thread_fn,
 #error Unsupported Xtensa ABI
 #endif
 
-	if (!(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+	if (!(p->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		struct pt_regs *regs = current_pt_regs();
 		unsigned long usp = usp_thread_fn ?
 			usp_thread_fn : regs->areg[1];
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f5b2be39a78c..1a749940cfde 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1691,6 +1691,7 @@ extern struct pid *cad_pid;
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
 #define PF_SWAPWRITE		0x00800000	/* Allowed to write to swap */
+#define PF_USER_WORKER		0x01000000	/* Kernel thread cloned from userspace
thread */
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with
cpus_mask */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
 #define PF_MEMALLOC_PIN		0x10000000	/* Allocation context constrained to zones
which allow long term pinning. */
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 0bf95966ae7d..0467b3ce1c94 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -18,7 +18,8 @@ struct css_set;
 /* All the bits taken by the old clone syscall. */
 #define CLONE_LEGACY_FLAGS 0xffffffffULL
 
-#define USER_WORKER_IO		BIT(0)
+#define USER_WORKER		BIT(0)
+#define USER_WORKER_IO		BIT(1)
 
 struct kernel_clone_args {
 	u64 flags;
diff --git a/kernel/fork.c b/kernel/fork.c
index 9273fd81a329..1f6e7184b31f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1998,6 +1998,10 @@ static __latent_entropy struct task_struct *copy_process(
 	p = dup_task_struct(current, node);
 	if (!p)
 		goto fork_out;
+
+	if (args->worker_flags & USER_WORKER)
+		p->flags |= PF_USER_WORKER;
+
 	if (args->worker_flags & USER_WORKER_IO) {
 		/*
 		 * Mark us an IO worker, and block any signal that isn't
@@ -2497,7 +2501,7 @@ struct task_struct *create_io_thread(int (*fn)(void *),
void *arg, int node)
 		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
 		.stack		= (unsigned long)fn,
 		.stack_size	= (unsigned long)arg,
-		.worker_flags	= USER_WORKER_IO,
+		.worker_flags	= USER_WORKER | USER_WORKER_IO,
 	};
 
 	return copy_process(NULL, 0, node, &args);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 090bfb605ecf..bb85b454ff07 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1061,12 +1061,12 @@ void reclaim_throttle(pg_data_t *pgdat, enum
vmscan_throttle_state reason)
 	DEFINE_WAIT(wait);
 
 	/*
-	 * Do not throttle IO workers, kthreads other than kswapd or
+	 * Do not throttle user workers, kthreads other than kswapd or
 	 * workqueues. They may be required for reclaim to make
 	 * forward progress (e.g. journalling workqueues or kthreads).
 	 */
 	if (!current_is_kswapd() &&
-	    current->flags & (PF_IO_WORKER|PF_KTHREAD))
+	    current->flags & (PF_USER_WORKER|PF_KTHREAD))
 		return;
 
 	/*
-- 
2.25.1

Mike Christie

2022-Feb-02 21:01 UTC

head link

[PATCH 3/8] fork: add USER_WORKER flag to not dup/clone files

Each vhost device gets a thread that is used to perform IO and management
operations. Instead of a thread that is accessing a device, the thread is
part of the device, so when it creates a thread using a helper based on
copy_process we can't dup or clone the parent's files/FDS because it
would do an extra increment on ourself.

Later, when we do:

Qemu process exits:
        do_exit -> exit_files -> put_files_struct -> close_files

we would leak the device's resources because of that extra refcount
on the fd or file_struct.

This patch adds a no_files option so these worker threads can prevent
taking an extra refcount on themselves.

Signed-off-by: Mike Christie <michael.christie at oracle.com>
Acked-by: Christian Brauner <christian.brauner at ubuntu.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
---
 include/linux/sched/task.h |  1 +
 kernel/fork.c              | 11 +++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 0467b3ce1c94..706ca3dc3423 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -20,6 +20,7 @@ struct css_set;
 
 #define USER_WORKER		BIT(0)
 #define USER_WORKER_IO		BIT(1)
+#define USER_WORKER_NO_FILES	BIT(2)
 
 struct kernel_clone_args {
 	u64 flags;
diff --git a/kernel/fork.c b/kernel/fork.c
index 1f6e7184b31f..81a1096d6ee9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1530,7 +1530,8 @@ static int copy_fs(unsigned long clone_flags, struct
task_struct *tsk)
 	return 0;
 }
 
-static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
+static int copy_files(unsigned long clone_flags, struct task_struct *tsk,
+		      int no_files)
 {
 	struct files_struct *oldf, *newf;
 	int error = 0;
@@ -1542,6 +1543,11 @@ static int copy_files(unsigned long clone_flags, struct
task_struct *tsk)
 	if (!oldf)
 		goto out;
 
+	if (no_files) {
+		tsk->files = NULL;
+		goto out;
+	}
+
 	if (clone_flags & CLONE_FILES) {
 		atomic_inc(&oldf->count);
 		goto out;
@@ -2153,7 +2159,8 @@ static __latent_entropy struct task_struct *copy_process(
 	retval = copy_semundo(clone_flags, p);
 	if (retval)
 		goto bad_fork_cleanup_security;
-	retval = copy_files(clone_flags, p);
+	retval = copy_files(clone_flags, p,
+			    args->worker_flags & USER_WORKER_NO_FILES);
 	if (retval)
 		goto bad_fork_cleanup_semundo;
 	retval = copy_fs(clone_flags, p);
-- 
2.25.1

Mike Christie

2022-Feb-02 21:01 UTC

head link

[PATCH 4/8] fork: Add USER_WORKER flag to ignore signals

From: Christian Brauner <christian.brauner at ubuntu.com>

Since:

commit 10ab825bdef8 ("change kernel threads to ignore signals instead of
blocking them")

kthreads have been ignoring signals by default, and the vhost layer has
never had a need to change that. This patch adds an option flag,
USER_WORKER_SIG_IGN, handled in copy_process() after copy_sighand()
and copy_signals() so vhost_tasks added in the next patches can continue
to ignore singals.

Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
Signed-off-by: Mike Christie <michael.christie at oracle.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
---
 include/linux/sched/task.h | 1 +
 kernel/fork.c              | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 706ca3dc3423..c001d0fa1426 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -21,6 +21,7 @@ struct css_set;
 #define USER_WORKER		BIT(0)
 #define USER_WORKER_IO		BIT(1)
 #define USER_WORKER_NO_FILES	BIT(2)
+#define USER_WORKER_SIG_IGN	BIT(3)
 
 struct kernel_clone_args {
 	u64 flags;
diff --git a/kernel/fork.c b/kernel/fork.c
index 81a1096d6ee9..6a04860fa1ae 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2185,6 +2185,9 @@ static __latent_entropy struct task_struct *copy_process(
 	if (retval)
 		goto bad_fork_cleanup_io;
 
+	if (args->worker_flags & USER_WORKER_SIG_IGN)
+		ignore_signals(p);
+
 	stackleak_task_init(p);
 
 	if (pid != &init_struct_pid) {
-- 
2.25.1

Mike Christie

2022-Feb-02 21:01 UTC

head link

[PATCH 5/8] fork: allow kernel code to call copy_process

The next patch adds helpers like create_io_thread, but for use by the
vhost layer. There are several functions, so they are in their own file
instead of cluttering up fork.c. This patch allows that new file to
call copy_process.

Signed-off-by: Mike Christie <michael.christie at oracle.com>
---
 include/linux/sched/task.h | 2 ++
 kernel/fork.c              | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index c001d0fa1426..787e6108fd65 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -90,6 +90,8 @@ extern void exit_files(struct task_struct *);
 extern void exit_itimers(struct signal_struct *);
 
 extern pid_t kernel_clone(struct kernel_clone_args *kargs);
+struct task_struct *copy_process(struct pid *pid, int trace, int node,
+				 struct kernel_clone_args *args);
 struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node);
 struct task_struct *fork_idle(int);
 struct mm_struct *copy_init_mm(void);
diff --git a/kernel/fork.c b/kernel/fork.c
index 6a04860fa1ae..04eb7fc50a13 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1905,7 +1905,7 @@ static void copy_oom_score_adj(u64 clone_flags, struct
task_struct *tsk)
  * parts of the process environment (as per the clone
  * flags). The actual kick-off is left to the caller.
  */
-static __latent_entropy struct task_struct *copy_process(
+__latent_entropy struct task_struct *copy_process(
 					struct pid *pid,
 					int trace,
 					int node,
-- 
2.25.1

Mike Christie

2022-Feb-02 21:01 UTC

head link

[PATCH 6/8] vhost_task: Allow vhost layer to use copy_process

Qemu will create vhost devices in the kernel which perform network, SCSI,
etc IO and management operations from worker threads created by the
kthread API. Because the kthread API does a copy_process on the kthreadd
thread, the vhost layer has to use kthread_use_mm to access the Qemu
thread's memory and cgroup_attach_task_all to add itself to the Qemu
thread's cgroups, and it bypasses the RLIMIT_NPROC limit.

This patch adds a new struct vhost_task which can be used instead of
kthreads. They allow the vhost layer to use copy_process and inherit
the userspace process's mm and cgroups and the task is accounted for
under the userspace's nproc count.

Signed-off-by: Mike Christie <michael.christie at oracle.com>
---
 MAINTAINERS                      |   2 +
 drivers/vhost/Kconfig            |   5 ++
 include/linux/sched/vhost_task.h |  23 ++++++
 kernel/Makefile                  |   1 +
 kernel/vhost_task.c              | 123 +++++++++++++++++++++++++++++++
 5 files changed, 154 insertions(+)
 create mode 100644 include/linux/sched/vhost_task.h
 create mode 100644 kernel/vhost_task.c

diff --git a/MAINTAINERS b/MAINTAINERS
index f41088418aae..0d595f2ef4ae 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20464,7 +20464,9 @@ L:	virtualization at lists.linux-foundation.org
 L:	netdev at vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git
+F:	kernel/vhost_task.c
 F:	drivers/vhost/
+F:	include/linux/sched/vhost_task.h
 F:	include/linux/vhost_iotlb.h
 F:	include/uapi/linux/vhost.h
 
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 587fbae06182..b455d9ab6f3d 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -13,9 +13,14 @@ config VHOST_RING
 	  This option is selected by any driver which needs to access
 	  the host side of a virtio ring.
 
+config VHOST_TASK
+	bool
+	default n
+
 config VHOST
 	tristate
 	select VHOST_IOTLB
+	select VHOST_TASK
 	help
 	  This option is selected by any driver which needs to access
 	  the core of vhost.
diff --git a/include/linux/sched/vhost_task.h b/include/linux/sched/vhost_task.h
new file mode 100644
index 000000000000..50d02a25d37b
--- /dev/null
+++ b/include/linux/sched/vhost_task.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_VHOST_TASK_H
+#define _LINUX_VHOST_TASK_H
+
+#include <linux/completion.h>
+
+struct task_struct;
+
+struct vhost_task {
+	int (*fn)(void *data);
+	void *data;
+	struct completion exited;
+	unsigned long flags;
+	struct task_struct *task;
+};
+
+struct vhost_task *vhost_task_create(int (*fn)(void *), void *arg, int node);
+__printf(2, 3)
+void vhost_task_start(struct vhost_task *vtsk, const char namefmt[], ...);
+void vhost_task_stop(struct vhost_task *vtsk);
+bool vhost_task_should_stop(struct vhost_task *vtsk);
+
+#endif
diff --git a/kernel/Makefile b/kernel/Makefile
index 56f4ee97f328..d82f388082b8 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -15,6 +15,7 @@ obj-y     = fork.o exec_domain.o panic.o \
 obj-$(CONFIG_USERMODE_DRIVER) += usermode_driver.o
 obj-$(CONFIG_MODULES) += kmod.o
 obj-$(CONFIG_MULTIUSER) += groups.o
+obj-$(CONFIG_VHOST_TASK) += vhost_task.o
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace internal ftrace files
diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c
new file mode 100644
index 000000000000..cdf875617656
--- /dev/null
+++ b/kernel/vhost_task.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 Oracle Corporation
+ */
+#include <linux/slab.h>
+#include <linux/completion.h>
+#include <linux/sched/task.h>
+#include <linux/sched/vhost_task.h>
+#include <linux/sched/signal.h>
+
+enum vhost_task_flags {
+	VHOST_TASK_FLAGS_STOP,
+};
+
+static void vhost_task_fn(void *data)
+{
+	struct vhost_task *vtsk = data;
+	int ret;
+
+	ret = vtsk->fn(vtsk->data);
+	complete(&vtsk->exited);
+	do_exit(ret);
+}
+
+/**
+ * vhost_task_stop - stop a vhost_task
+ * @vtsk: vhost_task to stop
+ *
+ * Callers must call vhost_task_should_stop and return from their worker
+ * function when it returns true;
+ */
+void vhost_task_stop(struct vhost_task *vtsk)
+{
+	pid_t pid = vtsk->task->pid;
+
+	set_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags);
+	wake_up_process(vtsk->task);
+	/*
+	 * Make sure vhost_task_fn is no longer accessing the vhost_task before
+	 * freeing it below. If userspace crashed or exited without closing,
+	 * then the vhost_task->task could already be marked dead so
+	 * kernel_wait will return early.
+	 */
+	wait_for_completion(&vtsk->exited);
+	/*
+	 * If we are just closing/removing a device and the parent process is
+	 * not exiting then reap the task.
+	 */
+	kernel_wait4(pid, NULL, __WCLONE, NULL);
+	kfree(vtsk);
+}
+EXPORT_SYMBOL_GPL(vhost_task_stop);
+
+/**
+ * vhost_task_should_stop - should the vhost task return from the work function
+ */
+bool vhost_task_should_stop(struct vhost_task *vtsk)
+{
+	return test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags);
+}
+EXPORT_SYMBOL_GPL(vhost_task_should_stop);
+
+/**
+ * vhost_task_create - create a copy of a process to be used by the kernel
+ * @fn: thread stack
+ * @arg: data to be passed to fn
+ * @node: numa node to allocate task from
+ *
+ * This returns a specialized task for use by the vhost layer or NULL on
+ * failure. The returned task is inactive, and the caller must fire it up
+ * through vhost_task_start().
+ */
+struct vhost_task *vhost_task_create(int (*fn)(void *), void *arg, int node)
+{
+	struct kernel_clone_args args = {
+		.flags		= CLONE_FS | CLONE_UNTRACED | CLONE_VM,
+		.exit_signal	= 0,
+		.stack		= (unsigned long)vhost_task_fn,
+		.worker_flags	= USER_WORKER | USER_WORKER_NO_FILES |
+				  USER_WORKER_SIG_IGN,
+	};
+	struct vhost_task *vtsk;
+	struct task_struct *tsk;
+
+	vtsk = kzalloc(GFP_KERNEL, sizeof(*vtsk));
+	if (!vtsk)
+		return ERR_PTR(-ENOMEM);
+
+	init_completion(&vtsk->exited);
+	vtsk->data = arg;
+	vtsk->fn = fn;
+	args.stack_size =  (unsigned long)vtsk;
+
+	tsk = copy_process(NULL, 0, node, &args);
+	if (IS_ERR(tsk)) {
+		kfree(vtsk);
+		return NULL;
+	}
+
+	vtsk->task = tsk;
+
+	return vtsk;
+}
+EXPORT_SYMBOL_GPL(vhost_task_create);
+
+/**
+ * vhost_task_start - start a vhost_task created with vhost_task_create
+ * @vtsk: vhost_task to wake up
+ * @namefmt: printf-style format string for the thread name
+ */
+void vhost_task_start(struct vhost_task *vtsk, const char namefmt[], ...)
+{
+	char name[TASK_COMM_LEN];
+	va_list args;
+
+	va_start(args, namefmt);
+	vsnprintf(name, sizeof(name), namefmt, args);
+	set_task_comm(vtsk->task, name);
+	va_end(args);
+
+	wake_up_new_task(vtsk->task);
+}
+EXPORT_SYMBOL_GPL(vhost_task_start);
-- 
2.25.1

Mike Christie

2022-Feb-02 21:01 UTC

head link

[PATCH 7/8] vhost: move worker thread fields to new struct

This is just a prep patch. It moves the worker related fields to a new
vhost_worker struct and moves the code around to create some helpers that
will be used in the next patch.

Signed-off-by: Mike Christie <michael.christie at oracle.com>
Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
---
 drivers/vhost/vhost.c | 98 ++++++++++++++++++++++++++++---------------
 drivers/vhost/vhost.h | 11 +++--
 2 files changed, 72 insertions(+), 37 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 59edb5a1ffe2..c9a1f706989c 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -263,8 +263,8 @@ void vhost_work_queue(struct vhost_dev *dev, struct
vhost_work *work)
 		 * sure it was not in the list.
 		 * test_and_set_bit() implies a memory barrier.
 		 */
-		llist_add(&work->node, &dev->work_list);
-		wake_up_process(dev->worker);
+		llist_add(&work->node, &dev->worker->work_list);
+		wake_up_process(dev->worker->task);
 	}
 }
 EXPORT_SYMBOL_GPL(vhost_work_queue);
@@ -272,7 +272,7 @@ EXPORT_SYMBOL_GPL(vhost_work_queue);
 /* A lockless hint for busy polling code to exit the loop */
 bool vhost_has_work(struct vhost_dev *dev)
 {
-	return !llist_empty(&dev->work_list);
+	return dev->worker &&
!llist_empty(&dev->worker->work_list);
 }
 EXPORT_SYMBOL_GPL(vhost_has_work);
 
@@ -343,7 +343,8 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 
 static int vhost_worker(void *data)
 {
-	struct vhost_dev *dev = data;
+	struct vhost_worker *worker = data;
+	struct vhost_dev *dev = worker->dev;
 	struct vhost_work *work, *work_next;
 	struct llist_node *node;
 
@@ -358,7 +359,7 @@ static int vhost_worker(void *data)
 			break;
 		}
 
-		node = llist_del_all(&dev->work_list);
+		node = llist_del_all(&worker->work_list);
 		if (!node)
 			schedule();
 
@@ -368,7 +369,7 @@ static int vhost_worker(void *data)
 		llist_for_each_entry_safe(work, work_next, node, node) {
 			clear_bit(VHOST_WORK_QUEUED, &work->flags);
 			__set_current_state(TASK_RUNNING);
-			kcov_remote_start_common(dev->kcov_handle);
+			kcov_remote_start_common(worker->kcov_handle);
 			work->fn(work);
 			kcov_remote_stop();
 			if (need_resched())
@@ -487,7 +488,6 @@ void vhost_dev_init(struct vhost_dev *dev,
 	dev->byte_weight = byte_weight;
 	dev->use_worker = use_worker;
 	dev->msg_handler = msg_handler;
-	init_llist_head(&dev->work_list);
 	init_waitqueue_head(&dev->wait);
 	INIT_LIST_HEAD(&dev->read_list);
 	INIT_LIST_HEAD(&dev->pending_list);
@@ -579,10 +579,60 @@ static void vhost_detach_mm(struct vhost_dev *dev)
 	dev->mm = NULL;
 }
 
+static void vhost_worker_free(struct vhost_dev *dev)
+{
+	struct vhost_worker *worker = dev->worker;
+
+	if (!worker)
+		return;
+
+	dev->worker = NULL;
+	WARN_ON(!llist_empty(&worker->work_list));
+	kthread_stop(worker->task);
+	kfree(worker);
+}
+
+static int vhost_worker_create(struct vhost_dev *dev)
+{
+	struct vhost_worker *worker;
+	struct task_struct *task;
+	int ret;
+
+	worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
+	if (!worker)
+		return -ENOMEM;
+
+	dev->worker = worker;
+	worker->dev = dev;
+	worker->kcov_handle = kcov_common_handle();
+	init_llist_head(&worker->work_list);
+
+	task = kthread_create(vhost_worker, worker, "vhost-%d",
current->pid);
+	if (IS_ERR(task)) {
+		ret = PTR_ERR(task);
+		goto free_worker;
+	}
+
+	worker->task = task;
+	wake_up_process(task); /* avoid contributing to loadavg */
+
+	ret = vhost_attach_cgroups(dev);
+	if (ret)
+		goto stop_worker;
+
+	return 0;
+
+stop_worker:
+	kthread_stop(worker->task);
+free_worker:
+	kfree(worker);
+	dev->worker = NULL;
+	return ret;
+}
+
 /* Caller should have device mutex */
 long vhost_dev_set_owner(struct vhost_dev *dev)
 {
-	struct task_struct *worker;
 	int err;
 
 	/* Is there an owner already? */
@@ -593,36 +643,21 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
 
 	vhost_attach_mm(dev);
 
-	dev->kcov_handle = kcov_common_handle();
 	if (dev->use_worker) {
-		worker = kthread_create(vhost_worker, dev,
-					"vhost-%d", current->pid);
-		if (IS_ERR(worker)) {
-			err = PTR_ERR(worker);
-			goto err_worker;
-		}
-
-		dev->worker = worker;
-		wake_up_process(worker); /* avoid contributing to loadavg */
-
-		err = vhost_attach_cgroups(dev);
+		err = vhost_worker_create(dev);
 		if (err)
-			goto err_cgroup;
+			goto err_worker;
 	}
 
 	err = vhost_dev_alloc_iovecs(dev);
 	if (err)
-		goto err_cgroup;
+		goto err_iovecs;
 
 	return 0;
-err_cgroup:
-	if (dev->worker) {
-		kthread_stop(dev->worker);
-		dev->worker = NULL;
-	}
+err_iovecs:
+	vhost_worker_free(dev);
 err_worker:
 	vhost_detach_mm(dev);
-	dev->kcov_handle = 0;
 err_mm:
 	return err;
 }
@@ -712,12 +747,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
 	dev->iotlb = NULL;
 	vhost_clear_msg(dev);
 	wake_up_interruptible_poll(&dev->wait, EPOLLIN | EPOLLRDNORM);
-	WARN_ON(!llist_empty(&dev->work_list));
-	if (dev->worker) {
-		kthread_stop(dev->worker);
-		dev->worker = NULL;
-		dev->kcov_handle = 0;
-	}
+	vhost_worker_free(dev);
 	vhost_detach_mm(dev);
 }
 EXPORT_SYMBOL_GPL(vhost_dev_cleanup);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 638bb640d6b4..102ce25e4e13 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -25,6 +25,13 @@ struct vhost_work {
 	unsigned long		flags;
 };
 
+struct vhost_worker {
+	struct task_struct	*task;
+	struct llist_head	work_list;
+	struct vhost_dev	*dev;
+	u64			kcov_handle;
+};
+
 /* Poll a file (eventfd or socket) */
 /* Note: there's nothing vhost specific about this structure. */
 struct vhost_poll {
@@ -148,8 +155,7 @@ struct vhost_dev {
 	struct vhost_virtqueue **vqs;
 	int nvqs;
 	struct eventfd_ctx *log_ctx;
-	struct llist_head work_list;
-	struct task_struct *worker;
+	struct vhost_worker *worker;
 	struct vhost_iotlb *umem;
 	struct vhost_iotlb *iotlb;
 	spinlock_t iotlb_lock;
@@ -159,7 +165,6 @@ struct vhost_dev {
 	int iov_limit;
 	int weight;
 	int byte_weight;
-	u64 kcov_handle;
 	bool use_worker;
 	int (*msg_handler)(struct vhost_dev *dev,
 			   struct vhost_iotlb_msg *msg);
-- 
2.25.1

Mike Christie

2022-Feb-02 21:02 UTC

head link

[PATCH 8/8] vhost: use vhost_tasks for worker threads

For vhost workers we use the kthread API which inherit's its values from
and checks against the kthreadd thread. This results in the wrong RLIMITs
being checked, so while tools like libvirt try to control the number of
threads based on the nproc rlimit setting we can end up creating more
threads than the user wanted.

This patch has us use the vhost_task helpers which will inherit its
values/checks from the thread that owns the device similar to if we did
a clone in userspace.

Signed-off-by: Mike Christie <michael.christie at oracle.com>
---
 drivers/vhost/vhost.c | 58 ++++++++-----------------------------------
 drivers/vhost/vhost.h |  4 +--
 2 files changed, 13 insertions(+), 49 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c9a1f706989c..ce356f5dc751 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -22,11 +22,11 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/kthread.h>
-#include <linux/cgroup.h>
 #include <linux/module.h>
 #include <linux/sort.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/vhost_task.h>
 #include <linux/interval_tree_generic.h>
 #include <linux/nospec.h>
 #include <linux/kcov.h>
@@ -264,7 +264,7 @@ void vhost_work_queue(struct vhost_dev *dev, struct
vhost_work *work)
 		 * test_and_set_bit() implies a memory barrier.
 		 */
 		llist_add(&work->node, &dev->worker->work_list);
-		wake_up_process(dev->worker->task);
+		wake_up_process(dev->worker->vtsk->task);
 	}
 }
 EXPORT_SYMBOL_GPL(vhost_work_queue);
@@ -344,17 +344,14 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 static int vhost_worker(void *data)
 {
 	struct vhost_worker *worker = data;
-	struct vhost_dev *dev = worker->dev;
 	struct vhost_work *work, *work_next;
 	struct llist_node *node;
 
-	kthread_use_mm(dev->mm);
-
 	for (;;) {
 		/* mb paired w/ kthread_stop */
 		set_current_state(TASK_INTERRUPTIBLE);
 
-		if (kthread_should_stop()) {
+		if (vhost_task_should_stop(worker->vtsk)) {
 			__set_current_state(TASK_RUNNING);
 			break;
 		}
@@ -376,7 +373,7 @@ static int vhost_worker(void *data)
 				schedule();
 		}
 	}
-	kthread_unuse_mm(dev->mm);
+
 	return 0;
 }
 
@@ -517,31 +514,6 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
 }
 EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
 
-struct vhost_attach_cgroups_struct {
-	struct vhost_work work;
-	struct task_struct *owner;
-	int ret;
-};
-
-static void vhost_attach_cgroups_work(struct vhost_work *work)
-{
-	struct vhost_attach_cgroups_struct *s;
-
-	s = container_of(work, struct vhost_attach_cgroups_struct, work);
-	s->ret = cgroup_attach_task_all(s->owner, current);
-}
-
-static int vhost_attach_cgroups(struct vhost_dev *dev)
-{
-	struct vhost_attach_cgroups_struct attach;
-
-	attach.owner = current;
-	vhost_work_init(&attach.work, vhost_attach_cgroups_work);
-	vhost_work_queue(dev, &attach.work);
-	vhost_work_dev_flush(dev);
-	return attach.ret;
-}
-
 /* Caller should have device mutex */
 bool vhost_dev_has_owner(struct vhost_dev *dev)
 {
@@ -588,14 +560,14 @@ static void vhost_worker_free(struct vhost_dev *dev)
 
 	dev->worker = NULL;
 	WARN_ON(!llist_empty(&worker->work_list));
-	kthread_stop(worker->task);
+	vhost_task_stop(worker->vtsk);
 	kfree(worker);
 }
 
 static int vhost_worker_create(struct vhost_dev *dev)
 {
 	struct vhost_worker *worker;
-	struct task_struct *task;
+	struct vhost_task *vtsk;
 	int ret;
 
 	worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
@@ -603,27 +575,19 @@ static int vhost_worker_create(struct vhost_dev *dev)
 		return -ENOMEM;
 
 	dev->worker = worker;
-	worker->dev = dev;
 	worker->kcov_handle = kcov_common_handle();
 	init_llist_head(&worker->work_list);
 
-	task = kthread_create(vhost_worker, worker, "vhost-%d",
current->pid);
-	if (IS_ERR(task)) {
-		ret = PTR_ERR(task);
+	vtsk = vhost_task_create(vhost_worker, worker, NUMA_NO_NODE);
+	if (!vtsk) {
+		ret = -ENOMEM;
 		goto free_worker;
 	}
 
-	worker->task = task;
-	wake_up_process(task); /* avoid contributing to loadavg */
-
-	ret = vhost_attach_cgroups(dev);
-	if (ret)
-		goto stop_worker;
-
+	worker->vtsk = vtsk;
+	vhost_task_start(vtsk, "vhost-%d", current->pid);
 	return 0;
 
-stop_worker:
-	kthread_stop(worker->task);
 free_worker:
 	kfree(worker);
 	dev->worker = NULL;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 102ce25e4e13..c9f391326dd5 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -16,6 +16,7 @@
 #include <linux/irqbypass.h>
 
 struct vhost_work;
+struct vhost_task;
 typedef void (*vhost_work_fn_t)(struct vhost_work *work);
 
 #define VHOST_WORK_QUEUED 1
@@ -26,9 +27,8 @@ struct vhost_work {
 };
 
 struct vhost_worker {
-	struct task_struct	*task;
+	struct vhost_task	*vtsk;
 	struct llist_head	work_list;
-	struct vhost_dev	*dev;
 	u64			kcov_handle;
 };
 
-- 
2.25.1

Virtualization - Feb 2022 - [PATCH 8/8] vhost: use vhost_tasks for worker threads

[PATCH 0/8] Use copy_process in vhost layer

[PATCH 1/8] fork: Make IO worker options flag based

[PATCH 2/8] fork/vm: Move common PF_IO_WORKER behavior to new flag

[PATCH 3/8] fork: add USER_WORKER flag to not dup/clone files

[PATCH 4/8] fork: Add USER_WORKER flag to ignore signals

[PATCH 5/8] fork: allow kernel code to call copy_process

[PATCH 6/8] vhost_task: Allow vhost layer to use copy_process

[PATCH 7/8] vhost: move worker thread fields to new struct

[PATCH 8/8] vhost: use vhost_tasks for worker threads