Mike Christie
2023-May-22 02:51 UTC
[PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression
When switching from kthreads to vhost_tasks two bugs were added:
1. The vhost worker tasks's now show up as processes so scripts doing ps
or ps a would not incorrectly detect the vhost task as another process.
2. kthreads disabled freeze by setting PF_NOFREEZE, but vhost tasks's
didn't disable or add support for them.
To fix both bugs, this switches the vhost task to be thread in the
process that does the VHOST_SET_OWNER ioctl, and has vhost_worker call
get_signal to support SIGKILL/SIGSTOP and freeze signals. Note that
SIGKILL/STOP support is required because CLONE_THREAD requires
CLONE_SIGHAND which requires those 2 signals to be suppported.
This a modified version of patch originally written by Linus which
handles his review comment to himself to rename ignore_signals to
block_signals to better represent what it now does. And it includes a
change to vhost_worker() to support SIGSTOP/KILL and freeze, and it
drops the wait use per Oleg's review comment that it's no longer needed
when using CLONE_THREAD.
Fixes: 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
Signed-off-by: Mike Christie <michael.christie at oracle.com>
---
drivers/vhost/vhost.c | 17 ++++++++++++++++-
include/linux/sched/task.h | 2 +-
kernel/fork.c | 12 +++---------
kernel/signal.c | 1 +
kernel/vhost_task.c | 16 ++++------------
5 files changed, 25 insertions(+), 23 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index a92af08e7864..bf83e9340e40 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -338,6 +338,7 @@ static int vhost_worker(void *data)
struct vhost_worker *worker = data;
struct vhost_work *work, *work_next;
struct llist_node *node;
+ bool dead = false;
for (;;) {
/* mb paired w/ kthread_stop */
@@ -349,8 +350,22 @@ static int vhost_worker(void *data)
}
node = llist_del_all(&worker->work_list);
- if (!node)
+ if (!node) {
schedule();
+ /*
+ * When we get a SIGKILL our release function will
+ * be called. That will stop new IOs from being queued
+ * and check for outstanding cmd responses. It will then
+ * call vhost_task_stop to tell us to return and exit.
+ */
+ if (!dead && signal_pending(current)) {
+ struct ksignal ksig;
+
+ dead = get_signal(&ksig);
+ if (dead)
+ clear_thread_flag(TIF_SIGPENDING);
+ }
+ }
node = llist_reverse_order(node);
/* make sure flag is seen after deletion */
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 537cbf9a2ade..249a5ece9def 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -29,7 +29,7 @@ struct kernel_clone_args {
u32 io_thread:1;
u32 user_worker:1;
u32 no_files:1;
- u32 ignore_signals:1;
+ u32 block_signals:1;
unsigned long stack;
unsigned long stack_size;
unsigned long tls;
diff --git a/kernel/fork.c b/kernel/fork.c
index ed4e01daccaa..9e04ab5c3946 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2338,14 +2338,10 @@ __latent_entropy struct task_struct *copy_process(
p->flags |= PF_KTHREAD;
if (args->user_worker)
p->flags |= PF_USER_WORKER;
- if (args->io_thread) {
- /*
- * Mark us an IO worker, and block any signal that isn't
- * fatal or STOP
- */
+ if (args->io_thread)
p->flags |= PF_IO_WORKER;
+ if (args->block_signals)
siginitsetinv(&p->blocked, sigmask(SIGKILL)|sigmask(SIGSTOP));
- }
if (args->name)
strscpy_pad(p->comm, args->name, sizeof(p->comm));
@@ -2517,9 +2513,6 @@ __latent_entropy struct task_struct *copy_process(
if (retval)
goto bad_fork_cleanup_io;
- if (args->ignore_signals)
- ignore_signals(p);
-
stackleak_task_init(p);
if (pid != &init_struct_pid) {
@@ -2861,6 +2854,7 @@ struct task_struct *create_io_thread(int (*fn)(void *),
void *arg, int node)
.fn_arg = arg,
.io_thread = 1,
.user_worker = 1,
+ .block_signals = 1,
};
return copy_process(NULL, 0, node, &args);
diff --git a/kernel/signal.c b/kernel/signal.c
index 8050fe23c732..a0f00a078cbb 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2891,6 +2891,7 @@ bool get_signal(struct ksignal *ksig)
return ksig->sig > 0;
}
+EXPORT_SYMBOL_GPL(get_signal);
/**
* signal_delivered - called after signal delivery to update blocked signals
diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c
index b7cbd66f889e..7a2d7d9fe772 100644
--- a/kernel/vhost_task.c
+++ b/kernel/vhost_task.c
@@ -31,22 +31,13 @@ static int vhost_task_fn(void *data)
*/
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.
+ * freeing it below.
*/
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);
@@ -75,13 +66,14 @@ struct vhost_task *vhost_task_create(int (*fn)(void *), void
*arg,
const char *name)
{
struct kernel_clone_args args = {
- .flags = CLONE_FS | CLONE_UNTRACED | CLONE_VM,
+ .flags = CLONE_FS | CLONE_UNTRACED | CLONE_VM |
+ CLONE_THREAD | CLONE_SIGHAND,
.exit_signal = 0,
.fn = vhost_task_fn,
.name = name,
.user_worker = 1,
.no_files = 1,
- .ignore_signals = 1,
+ .block_signals = 1,
};
struct vhost_task *vtsk;
struct task_struct *tsk;
--
2.25.1
Oleg Nesterov
2023-May-22 12:30 UTC
[PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression
Confused, please help... On 05/21, Mike Christie wrote:> > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -338,6 +338,7 @@ static int vhost_worker(void *data) > struct vhost_worker *worker = data; > struct vhost_work *work, *work_next; > struct llist_node *node; > + bool dead = false; > > for (;;) { > /* mb paired w/ kthread_stop */ > @@ -349,8 +350,22 @@ static int vhost_worker(void *data) > } > > node = llist_del_all(&worker->work_list); > - if (!node) > + if (!node) { > schedule(); > + /* > + * When we get a SIGKILL our release function will > + * be called. That will stop new IOs from being queued > + * and check for outstanding cmd responses. It will then > + * call vhost_task_stop to tell us to return and exit. > + */But who will call the release function / vhost_task_stop() and when this will happen after this thread gets SIGKILL ?> + if (!dead && signal_pending(current)) { > + struct ksignal ksig; > + > + dead = get_signal(&ksig); > + if (dead) > + clear_thread_flag(TIF_SIGPENDING);If you do clear_thread_flag(TIF_SIGPENDING), then why do we need 1/3 ? Also. Suppose that vhost_worker() dequeues SIGKILL and clears TIF_SIGPENDING. SIGSTOP, PTRACE_INTERRUPT, freezer can come and set TIF_SIGPENDING again. In this case the main for (;;) loop will spin without sleeping until vhost_task_should_stop() becomes true? Oleg.
Michael S. Tsirkin
2023-May-22 19:40 UTC
[PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression
On Sun, May 21, 2023 at 09:51:24PM -0500, Mike Christie wrote:> When switching from kthreads to vhost_tasks two bugs were added: > 1. The vhost worker tasks's now show up as processes so scripts doing ps > or ps a would not incorrectly detect the vhost task as another process. > 2. kthreads disabled freeze by setting PF_NOFREEZE, but vhost tasks's > didn't disable or add support for them. > > To fix both bugs, this switches the vhost task to be thread in the > process that does the VHOST_SET_OWNER ioctl, and has vhost_worker call > get_signal to support SIGKILL/SIGSTOP and freeze signals. Note that > SIGKILL/STOP support is required because CLONE_THREAD requires > CLONE_SIGHAND which requires those 2 signals to be suppported. > > This a modified version of patch originally written by Linus which > handles his review comment to himself to rename ignore_signals to > block_signals to better represent what it now does. And it includes a > change to vhost_worker() to support SIGSTOP/KILL and freeze, and it > drops the wait use per Oleg's review comment that it's no longer needed > when using CLONE_THREAD. > > Fixes: 6e890c5d5021 ("vhost: use vhost_tasks for worker threads") > Signed-off-by: Mike Christie <michael.christie at oracle.com> > --- > drivers/vhost/vhost.c | 17 ++++++++++++++++- > include/linux/sched/task.h | 2 +- > kernel/fork.c | 12 +++--------- > kernel/signal.c | 1 + > kernel/vhost_task.c | 16 ++++------------ > 5 files changed, 25 insertions(+), 23 deletions(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index a92af08e7864..bf83e9340e40 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -338,6 +338,7 @@ static int vhost_worker(void *data) > struct vhost_worker *worker = data; > struct vhost_work *work, *work_next; > struct llist_node *node; > + bool dead = false; > > for (;;) { > /* mb paired w/ kthread_stop */ > @@ -349,8 +350,22 @@ static int vhost_worker(void *data) > } > > node = llist_del_all(&worker->work_list); > - if (!node) > + if (!node) { > schedule(); > + /* > + * When we get a SIGKILL our release function will > + * be called. That will stop new IOs from being queued > + * and check for outstanding cmd responses. It will then > + * call vhost_task_stop to tell us to return and exit. > + */ > + if (!dead && signal_pending(current)) { > + struct ksignal ksig; > + > + dead = get_signal(&ksig); > + if (dead) > + clear_thread_flag(TIF_SIGPENDING);Does get_signal actually return true only on SIGKILL then?> + } > + } > > node = llist_reverse_order(node); > /* make sure flag is seen after deletion */ > diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h > index 537cbf9a2ade..249a5ece9def 100644 > --- a/include/linux/sched/task.h > +++ b/include/linux/sched/task.h > @@ -29,7 +29,7 @@ struct kernel_clone_args { > u32 io_thread:1; > u32 user_worker:1; > u32 no_files:1; > - u32 ignore_signals:1; > + u32 block_signals:1; > unsigned long stack; > unsigned long stack_size; > unsigned long tls; > diff --git a/kernel/fork.c b/kernel/fork.c > index ed4e01daccaa..9e04ab5c3946 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -2338,14 +2338,10 @@ __latent_entropy struct task_struct *copy_process( > p->flags |= PF_KTHREAD; > if (args->user_worker) > p->flags |= PF_USER_WORKER; > - if (args->io_thread) { > - /* > - * Mark us an IO worker, and block any signal that isn't > - * fatal or STOP > - */ > + if (args->io_thread) > p->flags |= PF_IO_WORKER; > + if (args->block_signals) > siginitsetinv(&p->blocked, sigmask(SIGKILL)|sigmask(SIGSTOP)); > - } > > if (args->name) > strscpy_pad(p->comm, args->name, sizeof(p->comm)); > @@ -2517,9 +2513,6 @@ __latent_entropy struct task_struct *copy_process( > if (retval) > goto bad_fork_cleanup_io; > > - if (args->ignore_signals) > - ignore_signals(p); > - > stackleak_task_init(p); > > if (pid != &init_struct_pid) { > @@ -2861,6 +2854,7 @@ struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node) > .fn_arg = arg, > .io_thread = 1, > .user_worker = 1, > + .block_signals = 1, > }; > > return copy_process(NULL, 0, node, &args); > diff --git a/kernel/signal.c b/kernel/signal.c > index 8050fe23c732..a0f00a078cbb 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -2891,6 +2891,7 @@ bool get_signal(struct ksignal *ksig) > > return ksig->sig > 0; > } > +EXPORT_SYMBOL_GPL(get_signal);If you are exporting this, could you add documentation please?> /** > * signal_delivered - called after signal delivery to update blocked signals > diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c > index b7cbd66f889e..7a2d7d9fe772 100644 > --- a/kernel/vhost_task.c > +++ b/kernel/vhost_task.c > @@ -31,22 +31,13 @@ static int vhost_task_fn(void *data) > */ > 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. > + * freeing it below. > */ > 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); > @@ -75,13 +66,14 @@ struct vhost_task *vhost_task_create(int (*fn)(void *), void *arg, > const char *name) > { > struct kernel_clone_args args = { > - .flags = CLONE_FS | CLONE_UNTRACED | CLONE_VM, > + .flags = CLONE_FS | CLONE_UNTRACED | CLONE_VM | > + CLONE_THREAD | CLONE_SIGHAND, > .exit_signal = 0, > .fn = vhost_task_fn, > .name = name, > .user_worker = 1, > .no_files = 1, > - .ignore_signals = 1, > + .block_signals = 1, > }; > struct vhost_task *vtsk; > struct task_struct *tsk; > -- > 2.25.1