search for: rwsem_can_spin_on_owner

...rudent, I decide to send this patch out. The race condition that I am looking at is as follows: ? CPU 0???????????????????????? CPU 1 ? -----???????????????????????? ----- up_write: ? owner = NULL; ? <release-barrier> ? count = 0; <rcu-free task structure> ? ????????????????????????? rwsem_can_spin_on_owner: ??????????????????????????? rcu_read_lock(); ??????????????????????????? read owner; ????????????????????????????? : ??????????????????????????? vcpu_is_preempted(owner->cpu); ????????????????????????????? : ??????????????????????????? rcu_read_unlock() When I tried to merge the owner into the...

...rudent, I decide to send this patch out. The race condition that I am looking at is as follows: ? CPU 0???????????????????????? CPU 1 ? -----???????????????????????? ----- up_write: ? owner = NULL; ? <release-barrier> ? count = 0; <rcu-free task structure> ? ????????????????????????? rwsem_can_spin_on_owner: ??????????????????????????? rcu_read_lock(); ??????????????????????????? read owner; ????????????????????????????? : ??????????????????????????? vcpu_is_preempted(owner->cpu); ????????????????????????????? : ??????????????????????????? rcu_read_unlock() When I tried to merge the owner into the...

...p; 0xff) && vcpu_is_preempted(task_cpu(owner)))) { ret = false; break; } diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 2ad8d8d..7a884a6 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -351,6 +351,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) { struct task_struct *owner = READ_ONCE(sem->owner); + int loop = 0; if (!rwsem_owner_is_writer(owner)) goto out; @@ -367,10 +368,11 @@ static noinline bool rwsem_spin_on_owner(struct rw_semap...

...ition that I am looking at is as follows: > > ? CPU 0???????????????????????? CPU 1 > ? -----???????????????????????? ----- > up_write: > ? owner = NULL; > ? <release-barrier> > ? count = 0; > > <rcu-free task structure> > ? > ????????????????????????? rwsem_can_spin_on_owner: > ??????????????????????????? rcu_read_lock(); > ??????????????????????????? read owner; > ????????????????????????????? : > ??????????????????????????? vcpu_is_preempted(owner->cpu); > ????????????????????????????? : > ??????????????????????????? rcu_read_unlock() > >...

...d_unlock(); /* * if lock->owner is not set, the mutex owner may have just acquired diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 09e30c6..99eb8fd 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -319,7 +319,11 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) goto done; } - ret = owner->on_cpu; + /* + * As lock holder preemption issue, we both skip spinning if task is not + * on cpu or its cpu is preempted + */ + ret = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner)); done: rcu_read_unlock(); re...

It was found that passing an invalid cpu number to pv_vcpu_is_preempted() might panic the kernel in a VM guest. For example, [ 2.531077] Oops: 0000 [#1] SMP PTI : [ 2.532545] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011 [ 2.533321] RIP: 0010:__raw_callee_save___kvm_vcpu_is_preempted+0x0/0x20 To guard against this kind of kernel panic, check is added to pv_vcpu_is_preempted() to

It was found that passing an invalid cpu number to pv_vcpu_is_preempted() might panic the kernel in a VM guest. For example, [ 2.531077] Oops: 0000 [#1] SMP PTI : [ 2.532545] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011 [ 2.533321] RIP: 0010:__raw_callee_save___kvm_vcpu_is_preempted+0x0/0x20 To guard against this kind of kernel panic, check is added to pv_vcpu_is_preempted() to

It was found when running fio sequential write test with a XFS ramdisk on a 2-socket x86-64 system, the %CPU times as reported by perf were as follows: 71.27% 0.28% fio [k] down_write 70.99% 0.01% fio [k] call_rwsem_down_write_failed 69.43% 1.18% fio [k] rwsem_down_write_failed 65.51% 54.57% fio [k] osq_lock 9.72% 7.99% fio [k] __raw_callee_save___kvm_vcpu_is_preempted 4.16%

It was found when running fio sequential write test with a XFS ramdisk on a 2-socket x86-64 system, the %CPU times as reported by perf were as follows: 71.27% 0.28% fio [k] down_write 70.99% 0.01% fio [k] call_rwsem_down_write_failed 69.43% 1.18% fio [k] rwsem_down_write_failed 65.51% 54.57% fio [k] osq_lock 9.72% 7.99% fio [k] __raw_callee_save___kvm_vcpu_is_preempted 4.16%

change from v2: no code change, fix typos, update some comments change from v1: a simplier definition of default vcpu_is_preempted skip mahcine type check on ppc, and add config. remove dedicated macro. add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. add more comments thanks boqun and Peter's suggestion. This patch set aims to fix lock holder preemption

change from v2: no code change, fix typos, update some comments change from v1: a simplier definition of default vcpu_is_preempted skip mahcine type check on ppc, and add config. remove dedicated macro. add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. add more comments thanks boqun and Peter's suggestion. This patch set aims to fix lock holder preemption

change fomr v1: a simplier definition of default vcpu_is_preempted skip mahcine type check on ppc, and add config. remove dedicated macro. add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. add more comments thanks boqun and Peter's suggestion. This patch set aims to fix lock holder preemption issues. test-case: perf record -a perf bench sched messaging -g

change fomr v1: a simplier definition of default vcpu_is_preempted skip mahcine type check on ppc, and add config. remove dedicated macro. add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. add more comments thanks boqun and Peter's suggestion. This patch set aims to fix lock holder preemption issues. test-case: perf record -a perf bench sched messaging -g

change from v4: spilt x86 kvm vcpu preempted check into two patches. add documentation patch. add x86 vcpu preempted check patch under xen add s390 vcpu preempted check patch change from v3: add x86 vcpu preempted check patch change from v2: no code change, fix typos, update some comments change from v1: a simplier definition of default vcpu_is_preempted skip mahcine type check on ppc,

change from v4: spilt x86 kvm vcpu preempted check into two patches. add documentation patch. add x86 vcpu preempted check patch under xen add s390 vcpu preempted check patch change from v3: add x86 vcpu preempted check patch change from v2: no code change, fix typos, update some comments change from v1: a simplier definition of default vcpu_is_preempted skip mahcine type check on ppc,

change from v3: add x86 vcpu preempted check patch change from v2: no code change, fix typos, update some comments change from v1: a simplier definition of default vcpu_is_preempted skip mahcine type check on ppc, and add config. remove dedicated macro. add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. add more comments thanks boqun and Peter's suggestion.

change from v3: add x86 vcpu preempted check patch change from v2: no code change, fix typos, update some comments change from v1: a simplier definition of default vcpu_is_preempted skip mahcine type check on ppc, and add config. remove dedicated macro. add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. add more comments thanks boqun and Peter's suggestion.

change from v6: fix typos and remove uncessary comments. change from v5: spilt x86/kvm patch into guest/host part. introduce kvm_write_guest_offset_cached. fix some typos. rebase patch onto 4.9.2 change from v4: spilt x86 kvm vcpu preempted check into two patches. add documentation patch. add x86 vcpu preempted check patch under xen add s390 vcpu preempted check patch change from v3:

change from v6: fix typos and remove uncessary comments. change from v5: spilt x86/kvm patch into guest/host part. introduce kvm_write_guest_offset_cached. fix some typos. rebase patch onto 4.9.2 change from v4: spilt x86 kvm vcpu preempted check into two patches. add documentation patch. add x86 vcpu preempted check patch under xen add s390 vcpu preempted check patch change from v3:

change from v5: spilt x86/kvm patch into guest/host part. introduce kvm_write_guest_offset_cached. fix some typos. rebase patch onto 4.9.2 change from v4: spilt x86 kvm vcpu preempted check into two patches. add documentation patch. add x86 vcpu preempted check patch under xen add s390 vcpu preempted check patch change from v3: add x86 vcpu preempted check patch change from v2: no code