lkml.org 
[lkml]   [2012]   [Jan]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: Hung task when calling clone() due to netfilter/slab
    From
    Date
    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 linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2012-01-15 18:29    [W:0.026 / U:30.416 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site