diff options
author | Tejun Heo <tj@kernel.org> | 2017-06-23 15:08:52 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-06-23 16:15:55 -0700 |
commit | 3b7b314053d021601940c50b07f5f1423ae67e21 (patch) | |
tree | a652f4da54d6e2b8916947969737bb04fbcb37a0 /mm/slub.c | |
parent | a91e0f680bcd9e10c253ae8b62462a38bd48f09f (diff) | |
download | linux-next-3b7b314053d021601940c50b07f5f1423ae67e21.tar.gz |
slub: make sysfs file removal asynchronous
Commit bf5eb3de3847 ("slub: separate out sysfs_slab_release() from
sysfs_slab_remove()") made slub sysfs file removals synchronous to
kmem_cache shutdown.
Unfortunately, this created a possible ABBA deadlock between slab_mutex
and sysfs draining mechanism triggering the following lockdep warning.
======================================================
[ INFO: possible circular locking dependency detected ]
4.10.0-test+ #48 Not tainted
-------------------------------------------------------
rmmod/1211 is trying to acquire lock:
(s_active#120){++++.+}, at: [<ffffffff81308073>] kernfs_remove+0x23/0x40
but task is already holding lock:
(slab_mutex){+.+.+.}, at: [<ffffffff8120f691>] kmem_cache_destroy+0x41/0x2d0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (slab_mutex){+.+.+.}:
lock_acquire+0xf6/0x1f0
__mutex_lock+0x75/0x950
mutex_lock_nested+0x1b/0x20
slab_attr_store+0x75/0xd0
sysfs_kf_write+0x45/0x60
kernfs_fop_write+0x13c/0x1c0
__vfs_write+0x28/0x120
vfs_write+0xc8/0x1e0
SyS_write+0x49/0xa0
entry_SYSCALL_64_fastpath+0x1f/0xc2
-> #0 (s_active#120){++++.+}:
__lock_acquire+0x10ed/0x1260
lock_acquire+0xf6/0x1f0
__kernfs_remove+0x254/0x320
kernfs_remove+0x23/0x40
sysfs_remove_dir+0x51/0x80
kobject_del+0x18/0x50
__kmem_cache_shutdown+0x3e6/0x460
kmem_cache_destroy+0x1fb/0x2d0
kvm_exit+0x2d/0x80 [kvm]
vmx_exit+0x19/0xa1b [kvm_intel]
SyS_delete_module+0x198/0x1f0
entry_SYSCALL_64_fastpath+0x1f/0xc2
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(slab_mutex);
lock(s_active#120);
lock(slab_mutex);
lock(s_active#120);
*** DEADLOCK ***
2 locks held by rmmod/1211:
#0: (cpu_hotplug.dep_map){++++++}, at: [<ffffffff810a7877>] get_online_cpus+0x37/0x80
#1: (slab_mutex){+.+.+.}, at: [<ffffffff8120f691>] kmem_cache_destroy+0x41/0x2d0
stack backtrace:
CPU: 3 PID: 1211 Comm: rmmod Not tainted 4.10.0-test+ #48
Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v02.05 05/07/2012
Call Trace:
print_circular_bug+0x1be/0x210
__lock_acquire+0x10ed/0x1260
lock_acquire+0xf6/0x1f0
__kernfs_remove+0x254/0x320
kernfs_remove+0x23/0x40
sysfs_remove_dir+0x51/0x80
kobject_del+0x18/0x50
__kmem_cache_shutdown+0x3e6/0x460
kmem_cache_destroy+0x1fb/0x2d0
kvm_exit+0x2d/0x80 [kvm]
vmx_exit+0x19/0xa1b [kvm_intel]
SyS_delete_module+0x198/0x1f0
? SyS_delete_module+0x5/0x1f0
entry_SYSCALL_64_fastpath+0x1f/0xc2
It'd be the cleanest to deal with the issue by removing sysfs files
without holding slab_mutex before the rest of shutdown; however, given
the current code structure, it is pretty difficult to do so.
This patch punts sysfs file removal to a work item. Before commit
bf5eb3de3847, the removal was punted to a RCU delayed work item which is
executed after release. Now, we're punting to a different work item on
shutdown which still maintains the goal removing the sysfs files earlier
when destroying kmem_caches.
Link: http://lkml.kernel.org/r/20170620204512.GI21326@htj.duckdns.org
Fixes: bf5eb3de3847 ("slub: separate out sysfs_slab_release() from sysfs_slab_remove()")
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/slub.c')
-rw-r--r-- | mm/slub.c | 40 |
1 files changed, 26 insertions, 14 deletions
diff --git a/mm/slub.c b/mm/slub.c index 7449593fca72..8addc535bcdc 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5625,6 +5625,28 @@ static char *create_unique_id(struct kmem_cache *s) return name; } +static void sysfs_slab_remove_workfn(struct work_struct *work) +{ + struct kmem_cache *s = + container_of(work, struct kmem_cache, kobj_remove_work); + + if (!s->kobj.state_in_sysfs) + /* + * For a memcg cache, this may be called during + * deactivation and again on shutdown. Remove only once. + * A cache is never shut down before deactivation is + * complete, so no need to worry about synchronization. + */ + return; + +#ifdef CONFIG_MEMCG + kset_unregister(s->memcg_kset); +#endif + kobject_uevent(&s->kobj, KOBJ_REMOVE); + kobject_del(&s->kobj); + kobject_put(&s->kobj); +} + static int sysfs_slab_add(struct kmem_cache *s) { int err; @@ -5632,6 +5654,8 @@ static int sysfs_slab_add(struct kmem_cache *s) struct kset *kset = cache_kset(s); int unmergeable = slab_unmergeable(s); + INIT_WORK(&s->kobj_remove_work, sysfs_slab_remove_workfn); + if (!kset) { kobject_init(&s->kobj, &slab_ktype); return 0; @@ -5695,20 +5719,8 @@ static void sysfs_slab_remove(struct kmem_cache *s) */ return; - if (!s->kobj.state_in_sysfs) - /* - * For a memcg cache, this may be called during - * deactivation and again on shutdown. Remove only once. - * A cache is never shut down before deactivation is - * complete, so no need to worry about synchronization. - */ - return; - -#ifdef CONFIG_MEMCG - kset_unregister(s->memcg_kset); -#endif - kobject_uevent(&s->kobj, KOBJ_REMOVE); - kobject_del(&s->kobj); + kobject_get(&s->kobj); + schedule_work(&s->kobj_remove_work); } void sysfs_slab_release(struct kmem_cache *s) |