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    SubjectRe: Hung task when calling clone() due to netfilter/slab
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    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

    --

    Sasha.



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