| Message ID | 20220812183033.346425-1-longman@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] mm/slab_common: Deleting kobject in kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock | expand |
On Fri, Aug 12, 2022 at 02:30:33PM -0400, Waiman Long wrote: > A circular locking problem is reported by lockdep due to the following > circular locking dependency. > > +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ > | | > +-----------------------------------------------------+ > > The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency > happens in > > kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); > ==> sysfs_slab_unlink() > ==> kobject_del() > ==> kernfs_remove() > ==> __kernfs_remove() > ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); Maybe you mean this? /* but everyone should wait for draining */ wait_event(root->deactivate_waitq, atomic_read(&kn->active) == KN_DEACTIVATED_BIAS); > The backward kn->active ==> cpu_hotplug_lock dependency happens in > > kernfs_fop_write_iter(): kernfs_get_active(); > ==> slab_attr_store() > ==> cpu_partial_store() > ==> flush_all(): cpus_read_lock() > > One way to break this circular locking chain is to avoid holding > cpu_hotplug_lock and slab_mutex while deleting the kobject in > sysfs_slab_unlink() which should be equivalent to doing a write_lock > and write_unlock pair of the kn->active virtual lock. > > Since the kobject structures are not protected by slab_mutex or the > cpu_hotplug_lock, we can certainly release those locks before doing > the delete operation. > > Move sysfs_slab_unlink() and sysfs_slab_release() to the newly > created kmem_cache_release() and call it outside the slab_mutex & > cpu_hotplug_lock critical sections. There will be a slight delay > in the deletion of sysfs files if kmem_cache_release() is called > indirectly from a work function. > > Signed-off-by: Waiman Long <longman@redhat.com> > --- > > [v3] Move sysfs_slab_unlink() out to kmem_cache_release() and move > schedule_work() back right after list_add_tail(). > > mm/slab_common.c | 45 +++++++++++++++++++++++++++++---------------- > 1 file changed, 29 insertions(+), 16 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 17996649cfe3..07b948288f84 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -392,6 +392,28 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align, > } > EXPORT_SYMBOL(kmem_cache_create); > > +#ifdef SLAB_SUPPORTS_SYSFS > +/* > + * For a given kmem_cache, kmem_cache_destroy() should only be called > + * once or there will be a use-after-free problem. The actual deletion > + * and release of the kobject does not need slab_mutex or cpu_hotplug_lock > + * protection. So they are now done without holding those locks. > + * > + * Note that there will be a slight delay in the deletion of sysfs files > + * if kmem_cache_release() is called indrectly from a work function. > + */ > +static void kmem_cache_release(struct kmem_cache *s) > +{ > + sysfs_slab_unlink(s); > + sysfs_slab_release(s); > +} > +#else > +static void kmem_cache_release(struct kmem_cache *s) > +{ > + slab_kmem_cache_release(s); > +} > +#endif > + > static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) > { > LIST_HEAD(to_destroy); > @@ -418,11 +440,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) > list_for_each_entry_safe(s, s2, &to_destroy, list) { > debugfs_slab_release(s); > kfence_shutdown_cache(s); > -#ifdef SLAB_SUPPORTS_SYSFS > - sysfs_slab_release(s); > -#else > - slab_kmem_cache_release(s); > -#endif > + kmem_cache_release(s); > } > } > > @@ -437,20 +455,11 @@ static int shutdown_cache(struct kmem_cache *s) > list_del(&s->list); > > if (s->flags & SLAB_TYPESAFE_BY_RCU) { > -#ifdef SLAB_SUPPORTS_SYSFS > - sysfs_slab_unlink(s); > -#endif > list_add_tail(&s->list, &slab_caches_to_rcu_destroy); > schedule_work(&slab_caches_to_rcu_destroy_work); > } else { > kfence_shutdown_cache(s); > debugfs_slab_release(s); > -#ifdef SLAB_SUPPORTS_SYSFS > - sysfs_slab_unlink(s); > - sysfs_slab_release(s); > -#else > - slab_kmem_cache_release(s); > -#endif > } > > return 0; > @@ -465,14 +474,16 @@ void slab_kmem_cache_release(struct kmem_cache *s) > > void kmem_cache_destroy(struct kmem_cache *s) > { > + int refcnt; > + > if (unlikely(!s) || !kasan_check_byte(s)) > return; > > cpus_read_lock(); > mutex_lock(&slab_mutex); > > - s->refcount--; > - if (s->refcount) > + refcnt = --s->refcount; > + if (refcnt) > goto out_unlock; > > WARN(shutdown_cache(s), > @@ -481,6 +492,8 @@ void kmem_cache_destroy(struct kmem_cache *s) > out_unlock: > mutex_unlock(&slab_mutex); > cpus_read_unlock(); > + if (!refcnt && !(s->flags & SLAB_TYPESAFE_BY_RCU)) > + kmem_cache_release(s); > } > EXPORT_SYMBOL(kmem_cache_destroy); > > -- > 2.31.1 > little bit complicated but looks good to me. Thank you for fixing this. Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
On Fri, Aug 12, 2022 at 02:30:33PM -0400, Waiman Long wrote: > A circular locking problem is reported by lockdep due to the following > circular locking dependency. > > +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ > | | > +-----------------------------------------------------+ > > The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency > happens in > > kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); > ==> sysfs_slab_unlink() > ==> kobject_del() > ==> kernfs_remove() > ==> __kernfs_remove() > ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); > > The backward kn->active ==> cpu_hotplug_lock dependency happens in > > kernfs_fop_write_iter(): kernfs_get_active(); > ==> slab_attr_store() > ==> cpu_partial_store() > ==> flush_all(): cpus_read_lock() > > One way to break this circular locking chain is to avoid holding > cpu_hotplug_lock and slab_mutex while deleting the kobject in > sysfs_slab_unlink() which should be equivalent to doing a write_lock > and write_unlock pair of the kn->active virtual lock. > > Since the kobject structures are not protected by slab_mutex or the > cpu_hotplug_lock, we can certainly release those locks before doing > the delete operation. > > Move sysfs_slab_unlink() and sysfs_slab_release() to the newly > created kmem_cache_release() and call it outside the slab_mutex & > cpu_hotplug_lock critical sections. There will be a slight delay > in the deletion of sysfs files if kmem_cache_release() is called > indirectly from a work function. > > Signed-off-by: Waiman Long <longman@redhat.com> Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev> Thank you, Waiman!
On Fri, 12 Aug 2022, Waiman Long wrote: > A circular locking problem is reported by lockdep due to the following > circular locking dependency. > > +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ > | | > +-----------------------------------------------------+ > > The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency > happens in > > kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); > ==> sysfs_slab_unlink() > ==> kobject_del() > ==> kernfs_remove() > ==> __kernfs_remove() > ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); > > The backward kn->active ==> cpu_hotplug_lock dependency happens in > > kernfs_fop_write_iter(): kernfs_get_active(); > ==> slab_attr_store() > ==> cpu_partial_store() > ==> flush_all(): cpus_read_lock() > > One way to break this circular locking chain is to avoid holding > cpu_hotplug_lock and slab_mutex while deleting the kobject in > sysfs_slab_unlink() which should be equivalent to doing a write_lock > and write_unlock pair of the kn->active virtual lock. > > Since the kobject structures are not protected by slab_mutex or the > cpu_hotplug_lock, we can certainly release those locks before doing > the delete operation. > > Move sysfs_slab_unlink() and sysfs_slab_release() to the newly > created kmem_cache_release() and call it outside the slab_mutex & > cpu_hotplug_lock critical sections. There will be a slight delay > in the deletion of sysfs files if kmem_cache_release() is called > indirectly from a work function. > > Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: David Rientjes <rientjes@google.com>
On 8/13/22 11:00, Hyeonggon Yoo wrote: > On Fri, Aug 12, 2022 at 02:30:33PM -0400, Waiman Long wrote: >> A circular locking problem is reported by lockdep due to the following >> circular locking dependency. >> >> +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ >> | | >> +-----------------------------------------------------+ >> >> The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency >> happens in >> >> kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); >> ==> sysfs_slab_unlink() >> ==> kobject_del() >> ==> kernfs_remove() >> ==> __kernfs_remove() >> ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); > Maybe you mean this? > > /* but everyone should wait for draining */ > wait_event(root->deactivate_waitq, > atomic_read(&kn->active) == KN_DEACTIVATED_BIAS); > This is part of the kernfs_drain() operation. However, I am focusing on the behavior of the pseudo lock that causes the lockdep splat in the first place. That is why I am showcasing the rwsem_acquire() call here. >> The backward kn->active ==> cpu_hotplug_lock dependency happens in >> >> kernfs_fop_write_iter(): kernfs_get_active(); >> ==> slab_attr_store() >> ==> cpu_partial_store() >> ==> flush_all(): cpus_read_lock() >> >> One way to break this circular locking chain is to avoid holding >> cpu_hotplug_lock and slab_mutex while deleting the kobject in >> sysfs_slab_unlink() which should be equivalent to doing a write_lock >> and write_unlock pair of the kn->active virtual lock. >> >> Since the kobject structures are not protected by slab_mutex or the >> cpu_hotplug_lock, we can certainly release those locks before doing >> the delete operation. >> >> Move sysfs_slab_unlink() and sysfs_slab_release() to the newly >> created kmem_cache_release() and call it outside the slab_mutex & >> cpu_hotplug_lock critical sections. There will be a slight delay >> in the deletion of sysfs files if kmem_cache_release() is called >> indirectly from a work function. >> >> Signed-off-by: Waiman Long <longman@redhat.com> >> --- >> >> [v3] Move sysfs_slab_unlink() out to kmem_cache_release() and move >> schedule_work() back right after list_add_tail(). >> >> mm/slab_common.c | 45 +++++++++++++++++++++++++++++---------------- >> 1 file changed, 29 insertions(+), 16 deletions(-) >> >> diff --git a/mm/slab_common.c b/mm/slab_common.c >> index 17996649cfe3..07b948288f84 100644 >> --- a/mm/slab_common.c >> +++ b/mm/slab_common.c >> @@ -392,6 +392,28 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align, >> } >> EXPORT_SYMBOL(kmem_cache_create); >> >> +#ifdef SLAB_SUPPORTS_SYSFS >> +/* >> + * For a given kmem_cache, kmem_cache_destroy() should only be called >> + * once or there will be a use-after-free problem. The actual deletion >> + * and release of the kobject does not need slab_mutex or cpu_hotplug_lock >> + * protection. So they are now done without holding those locks. >> + * >> + * Note that there will be a slight delay in the deletion of sysfs files >> + * if kmem_cache_release() is called indrectly from a work function. >> + */ >> +static void kmem_cache_release(struct kmem_cache *s) >> +{ >> + sysfs_slab_unlink(s); >> + sysfs_slab_release(s); >> +} >> +#else >> +static void kmem_cache_release(struct kmem_cache *s) >> +{ >> + slab_kmem_cache_release(s); >> +} >> +#endif >> + >> static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) >> { >> LIST_HEAD(to_destroy); >> @@ -418,11 +440,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) >> list_for_each_entry_safe(s, s2, &to_destroy, list) { >> debugfs_slab_release(s); >> kfence_shutdown_cache(s); >> -#ifdef SLAB_SUPPORTS_SYSFS >> - sysfs_slab_release(s); >> -#else >> - slab_kmem_cache_release(s); >> -#endif >> + kmem_cache_release(s); >> } >> } >> >> @@ -437,20 +455,11 @@ static int shutdown_cache(struct kmem_cache *s) >> list_del(&s->list); >> >> if (s->flags & SLAB_TYPESAFE_BY_RCU) { >> -#ifdef SLAB_SUPPORTS_SYSFS >> - sysfs_slab_unlink(s); >> -#endif >> list_add_tail(&s->list, &slab_caches_to_rcu_destroy); >> schedule_work(&slab_caches_to_rcu_destroy_work); >> } else { >> kfence_shutdown_cache(s); >> debugfs_slab_release(s); >> -#ifdef SLAB_SUPPORTS_SYSFS >> - sysfs_slab_unlink(s); >> - sysfs_slab_release(s); >> -#else >> - slab_kmem_cache_release(s); >> -#endif >> } >> >> return 0; >> @@ -465,14 +474,16 @@ void slab_kmem_cache_release(struct kmem_cache *s) >> >> void kmem_cache_destroy(struct kmem_cache *s) >> { >> + int refcnt; >> + >> if (unlikely(!s) || !kasan_check_byte(s)) >> return; >> >> cpus_read_lock(); >> mutex_lock(&slab_mutex); >> >> - s->refcount--; >> - if (s->refcount) >> + refcnt = --s->refcount; >> + if (refcnt) >> goto out_unlock; >> >> WARN(shutdown_cache(s), >> @@ -481,6 +492,8 @@ void kmem_cache_destroy(struct kmem_cache *s) >> out_unlock: >> mutex_unlock(&slab_mutex); >> cpus_read_unlock(); >> + if (!refcnt && !(s->flags & SLAB_TYPESAFE_BY_RCU)) >> + kmem_cache_release(s); >> } >> EXPORT_SYMBOL(kmem_cache_destroy); >> >> -- >> 2.31.1 >> > little bit complicated but looks good to me. > Thank you for fixing this. > > Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> > Thanks for the review. Cheers, Longman
On 8/13/22 14:25, Roman Gushchin wrote: > On Fri, Aug 12, 2022 at 02:30:33PM -0400, Waiman Long wrote: >> A circular locking problem is reported by lockdep due to the following >> circular locking dependency. >> >> +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ >> | | >> +-----------------------------------------------------+ >> >> The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency >> happens in >> >> kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); >> ==> sysfs_slab_unlink() >> ==> kobject_del() >> ==> kernfs_remove() >> ==> __kernfs_remove() >> ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); >> >> The backward kn->active ==> cpu_hotplug_lock dependency happens in >> >> kernfs_fop_write_iter(): kernfs_get_active(); >> ==> slab_attr_store() >> ==> cpu_partial_store() >> ==> flush_all(): cpus_read_lock() >> >> One way to break this circular locking chain is to avoid holding >> cpu_hotplug_lock and slab_mutex while deleting the kobject in >> sysfs_slab_unlink() which should be equivalent to doing a write_lock >> and write_unlock pair of the kn->active virtual lock. >> >> Since the kobject structures are not protected by slab_mutex or the >> cpu_hotplug_lock, we can certainly release those locks before doing >> the delete operation. >> >> Move sysfs_slab_unlink() and sysfs_slab_release() to the newly >> created kmem_cache_release() and call it outside the slab_mutex & >> cpu_hotplug_lock critical sections. There will be a slight delay >> in the deletion of sysfs files if kmem_cache_release() is called >> indirectly from a work function. >> >> Signed-off-by: Waiman Long <longman@redhat.com> > Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev> > > Thank you, Waiman! > Thanks for your suggestions that make this patch better. Cheers, Longman
On 8/12/22 20:30, Waiman Long wrote: > A circular locking problem is reported by lockdep due to the following > circular locking dependency. > > +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ > | | > +-----------------------------------------------------+ > > The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency > happens in > > kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); > ==> sysfs_slab_unlink() > ==> kobject_del() > ==> kernfs_remove() > ==> __kernfs_remove() > ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); > > The backward kn->active ==> cpu_hotplug_lock dependency happens in > > kernfs_fop_write_iter(): kernfs_get_active(); > ==> slab_attr_store() > ==> cpu_partial_store() > ==> flush_all(): cpus_read_lock() > > One way to break this circular locking chain is to avoid holding > cpu_hotplug_lock and slab_mutex while deleting the kobject in > sysfs_slab_unlink() which should be equivalent to doing a write_lock > and write_unlock pair of the kn->active virtual lock. > > Since the kobject structures are not protected by slab_mutex or the > cpu_hotplug_lock, we can certainly release those locks before doing > the delete operation. > > Move sysfs_slab_unlink() and sysfs_slab_release() to the newly > created kmem_cache_release() and call it outside the slab_mutex & > cpu_hotplug_lock critical sections. There will be a slight delay > in the deletion of sysfs files if kmem_cache_release() is called > indirectly from a work function. > > Signed-off-by: Waiman Long <longman@redhat.com> Thanks, added to slab.git for-6.0/fixes > --- > > [v3] Move sysfs_slab_unlink() out to kmem_cache_release() and move > schedule_work() back right after list_add_tail(). > > mm/slab_common.c | 45 +++++++++++++++++++++++++++++---------------- > 1 file changed, 29 insertions(+), 16 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 17996649cfe3..07b948288f84 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -392,6 +392,28 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align, > } > EXPORT_SYMBOL(kmem_cache_create); > > +#ifdef SLAB_SUPPORTS_SYSFS > +/* > + * For a given kmem_cache, kmem_cache_destroy() should only be called > + * once or there will be a use-after-free problem. The actual deletion > + * and release of the kobject does not need slab_mutex or cpu_hotplug_lock > + * protection. So they are now done without holding those locks. > + * > + * Note that there will be a slight delay in the deletion of sysfs files > + * if kmem_cache_release() is called indrectly from a work function. > + */ > +static void kmem_cache_release(struct kmem_cache *s) > +{ > + sysfs_slab_unlink(s); > + sysfs_slab_release(s); > +} > +#else > +static void kmem_cache_release(struct kmem_cache *s) > +{ > + slab_kmem_cache_release(s); > +} > +#endif > + > static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) > { > LIST_HEAD(to_destroy); > @@ -418,11 +440,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) > list_for_each_entry_safe(s, s2, &to_destroy, list) { > debugfs_slab_release(s); > kfence_shutdown_cache(s); > -#ifdef SLAB_SUPPORTS_SYSFS > - sysfs_slab_release(s); > -#else > - slab_kmem_cache_release(s); > -#endif > + kmem_cache_release(s); > } > } > > @@ -437,20 +455,11 @@ static int shutdown_cache(struct kmem_cache *s) > list_del(&s->list); > > if (s->flags & SLAB_TYPESAFE_BY_RCU) { > -#ifdef SLAB_SUPPORTS_SYSFS > - sysfs_slab_unlink(s); > -#endif > list_add_tail(&s->list, &slab_caches_to_rcu_destroy); > schedule_work(&slab_caches_to_rcu_destroy_work); > } else { > kfence_shutdown_cache(s); > debugfs_slab_release(s); > -#ifdef SLAB_SUPPORTS_SYSFS > - sysfs_slab_unlink(s); > - sysfs_slab_release(s); > -#else > - slab_kmem_cache_release(s); > -#endif > } > > return 0; > @@ -465,14 +474,16 @@ void slab_kmem_cache_release(struct kmem_cache *s) > > void kmem_cache_destroy(struct kmem_cache *s) > { > + int refcnt; > + > if (unlikely(!s) || !kasan_check_byte(s)) > return; > > cpus_read_lock(); > mutex_lock(&slab_mutex); > > - s->refcount--; > - if (s->refcount) > + refcnt = --s->refcount; > + if (refcnt) > goto out_unlock; > > WARN(shutdown_cache(s), > @@ -481,6 +492,8 @@ void kmem_cache_destroy(struct kmem_cache *s) > out_unlock: > mutex_unlock(&slab_mutex); > cpus_read_unlock(); > + if (!refcnt && !(s->flags & SLAB_TYPESAFE_BY_RCU)) > + kmem_cache_release(s); > } > EXPORT_SYMBOL(kmem_cache_destroy); >
On 8/23/22 07:33, Vlastimil Babka wrote: > On 8/12/22 20:30, Waiman Long wrote: >> A circular locking problem is reported by lockdep due to the following >> circular locking dependency. >> >> +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ >> | | >> +-----------------------------------------------------+ >> >> The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency >> happens in >> >> kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); >> ==> sysfs_slab_unlink() >> ==> kobject_del() >> ==> kernfs_remove() >> ==> __kernfs_remove() >> ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); >> >> The backward kn->active ==> cpu_hotplug_lock dependency happens in >> >> kernfs_fop_write_iter(): kernfs_get_active(); >> ==> slab_attr_store() >> ==> cpu_partial_store() >> ==> flush_all(): cpus_read_lock() >> >> One way to break this circular locking chain is to avoid holding >> cpu_hotplug_lock and slab_mutex while deleting the kobject in >> sysfs_slab_unlink() which should be equivalent to doing a write_lock >> and write_unlock pair of the kn->active virtual lock. >> >> Since the kobject structures are not protected by slab_mutex or the >> cpu_hotplug_lock, we can certainly release those locks before doing >> the delete operation. >> >> Move sysfs_slab_unlink() and sysfs_slab_release() to the newly >> created kmem_cache_release() and call it outside the slab_mutex & >> cpu_hotplug_lock critical sections. There will be a slight delay >> in the deletion of sysfs files if kmem_cache_release() is called >> indirectly from a work function. >> >> Signed-off-by: Waiman Long <longman@redhat.com> > Thanks, added to slab.git for-6.0/fixes Thanks for taking it. Cheers, Longman
diff --git a/mm/slab_common.c b/mm/slab_common.c index 17996649cfe3..07b948288f84 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -392,6 +392,28 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align, } EXPORT_SYMBOL(kmem_cache_create); +#ifdef SLAB_SUPPORTS_SYSFS +/* + * For a given kmem_cache, kmem_cache_destroy() should only be called + * once or there will be a use-after-free problem. The actual deletion + * and release of the kobject does not need slab_mutex or cpu_hotplug_lock + * protection. So they are now done without holding those locks. + * + * Note that there will be a slight delay in the deletion of sysfs files + * if kmem_cache_release() is called indrectly from a work function. + */ +static void kmem_cache_release(struct kmem_cache *s) +{ + sysfs_slab_unlink(s); + sysfs_slab_release(s); +} +#else +static void kmem_cache_release(struct kmem_cache *s) +{ + slab_kmem_cache_release(s); +} +#endif + static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) { LIST_HEAD(to_destroy); @@ -418,11 +440,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) list_for_each_entry_safe(s, s2, &to_destroy, list) { debugfs_slab_release(s); kfence_shutdown_cache(s); -#ifdef SLAB_SUPPORTS_SYSFS - sysfs_slab_release(s); -#else - slab_kmem_cache_release(s); -#endif + kmem_cache_release(s); } } @@ -437,20 +455,11 @@ static int shutdown_cache(struct kmem_cache *s) list_del(&s->list); if (s->flags & SLAB_TYPESAFE_BY_RCU) { -#ifdef SLAB_SUPPORTS_SYSFS - sysfs_slab_unlink(s); -#endif list_add_tail(&s->list, &slab_caches_to_rcu_destroy); schedule_work(&slab_caches_to_rcu_destroy_work); } else { kfence_shutdown_cache(s); debugfs_slab_release(s); -#ifdef SLAB_SUPPORTS_SYSFS - sysfs_slab_unlink(s); - sysfs_slab_release(s); -#else - slab_kmem_cache_release(s); -#endif } return 0; @@ -465,14 +474,16 @@ void slab_kmem_cache_release(struct kmem_cache *s) void kmem_cache_destroy(struct kmem_cache *s) { + int refcnt; + if (unlikely(!s) || !kasan_check_byte(s)) return; cpus_read_lock(); mutex_lock(&slab_mutex); - s->refcount--; - if (s->refcount) + refcnt = --s->refcount; + if (refcnt) goto out_unlock; WARN(shutdown_cache(s), @@ -481,6 +492,8 @@ void kmem_cache_destroy(struct kmem_cache *s) out_unlock: mutex_unlock(&slab_mutex); cpus_read_unlock(); + if (!refcnt && !(s->flags & SLAB_TYPESAFE_BY_RCU)) + kmem_cache_release(s); } EXPORT_SYMBOL(kmem_cache_destroy);
A circular locking problem is reported by lockdep due to the following circular locking dependency. +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ | | +-----------------------------------------------------+ The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency happens in kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); ==> sysfs_slab_unlink() ==> kobject_del() ==> kernfs_remove() ==> __kernfs_remove() ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); The backward kn->active ==> cpu_hotplug_lock dependency happens in kernfs_fop_write_iter(): kernfs_get_active(); ==> slab_attr_store() ==> cpu_partial_store() ==> flush_all(): cpus_read_lock() One way to break this circular locking chain is to avoid holding cpu_hotplug_lock and slab_mutex while deleting the kobject in sysfs_slab_unlink() which should be equivalent to doing a write_lock and write_unlock pair of the kn->active virtual lock. Since the kobject structures are not protected by slab_mutex or the cpu_hotplug_lock, we can certainly release those locks before doing the delete operation. Move sysfs_slab_unlink() and sysfs_slab_release() to the newly created kmem_cache_release() and call it outside the slab_mutex & cpu_hotplug_lock critical sections. There will be a slight delay in the deletion of sysfs files if kmem_cache_release() is called indirectly from a work function. Signed-off-by: Waiman Long <longman@redhat.com> --- [v3] Move sysfs_slab_unlink() out to kmem_cache_release() and move schedule_work() back right after list_add_tail(). mm/slab_common.c | 45 +++++++++++++++++++++++++++++---------------- 1 file changed, 29 insertions(+), 16 deletions(-)