| Message ID | 1326632384.11711.3.camel@lappy |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
Le dimanche 15 janvier 2012 à 14:59 +0200, Sasha Levin a écrit : > On Sat, 2012-01-14 at 18:10 +0100, Eric Dumazet wrote: > > Apparently SLUB calls sysfs_slab_add() from kmem_cache_create() while > > still holding slub_lock. > > > > So if the task launched needs to "cat /proc/slabinfo" or anything > > needing slub_lock, its a deadlock. > > I've made the following patch to test it, It doesn't look like it's > the correct solution, but it verifies that the problem is there (it > works well with the patch). > > --------------- > > From cc4874b491b8e5d9d1ea5bf2032413efdbddced8 Mon Sep 17 00:00:00 2001 > From: Sasha Levin <levinsasha928@gmail.com> > Date: Sun, 15 Jan 2012 14:55:03 +0200 > Subject: [PATCH] slab: Fix hang when creating sysfs entries > > This patch fixes the hang which happens when we create a sysfs entry and call > back to userspace. If the usermode helper tries to do anything which involves > slub_lock we will hang since slub_lock is already held. > > Signed-off-by: Sasha Levin <levinsasha928@gmail.com> > --- > mm/slub.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 4907563..6948327 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5283,7 +5283,9 @@ static int sysfs_slab_add(struct kmem_cache *s) > kobject_put(&s->kobj); > return err; > } > + up_write(&slub_lock); > kobject_uevent(&s->kobj, KOBJ_ADD); > + down_write(&slub_lock); > if (!unmergeable) { > /* Setup first alias */ > sysfs_slab_alias(s, s->name); > -- > 1.7.8.3 > > Oh well, that cannot be right. Dont send official patches if you already know "it's not the correct solution", we already know where is the problem. It's _never_ right to release a lock for a short time without any additional checks. [ If it was right, the lock would be not needed ] As soon as the slub_lock is released, another thread can come and find the new kmem_cache. For example, it can destroy it, and your thread is going to access s while it was already freed. sysfs_slab_alias(s, s->name); // crash -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/mm/slub.c b/mm/slub.c index 4907563..6948327 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5283,7 +5283,9 @@ static int sysfs_slab_add(struct kmem_cache *s) kobject_put(&s->kobj); return err; } + up_write(&slub_lock); kobject_uevent(&s->kobj, KOBJ_ADD); + down_write(&slub_lock); if (!unmergeable) { /* Setup first alias */ sysfs_slab_alias(s, s->name);