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    Subject[34-longterm 087/179] debugobjects: Fix boot crash when kmemleak and debugobjects enabled
    Date
    From: Marcin Slusarz <marcin.slusarz@gmail.com>

    -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
    -------------------

    commit 161b6ae0e067e421b20bb35caf66bdb405c929ac upstream.

    Order of initialization look like this:
    ...
    debugobjects
    kmemleak
    ...(lots of other subsystems)...
    workqueues (through early initcall)
    ...

    debugobjects use schedule_work for batch freeing of its data and kmemleak
    heavily use debugobjects, so when it comes to freeing and workqueues were
    not initialized yet, kernel crashes:

    BUG: unable to handle kernel NULL pointer dereference at (null)
    IP: [<ffffffff810854d1>] __queue_work+0x29/0x41a
    [<ffffffff81085910>] queue_work_on+0x16/0x1d
    [<ffffffff81085abc>] queue_work+0x29/0x55
    [<ffffffff81085afb>] schedule_work+0x13/0x15
    [<ffffffff81242de1>] free_object+0x90/0x95
    [<ffffffff81242f6d>] debug_check_no_obj_freed+0x187/0x1d3
    [<ffffffff814b6504>] ? _raw_spin_unlock_irqrestore+0x30/0x4d
    [<ffffffff8110bd14>] ? free_object_rcu+0x68/0x6d
    [<ffffffff8110890c>] kmem_cache_free+0x64/0x12c
    [<ffffffff8110bd14>] free_object_rcu+0x68/0x6d
    [<ffffffff810b58bc>] __rcu_process_callbacks+0x1b6/0x2d9
    ...

    because system_wq is NULL.

    Fix it by checking if workqueues susbystem was initialized before using.

    Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Dipankar Sarma <dipankar@in.ibm.com>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Link: http://lkml.kernel.org/r/20110528112342.GA3068@joi.lan
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
    ---
    lib/debugobjects.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/lib/debugobjects.c b/lib/debugobjects.c
    index b862b30..e60bd59 100644
    --- a/lib/debugobjects.c
    +++ b/lib/debugobjects.c
    @@ -197,7 +197,7 @@ static void free_object(struct debug_obj *obj)
    * initialized:
    */
    if (obj_pool_free > ODEBUG_POOL_SIZE && obj_cache)
    - sched = !work_pending(&debug_obj_work);
    + sched = keventd_up() && !work_pending(&debug_obj_work);
    hlist_add_head(&obj->node, &obj_pool);
    obj_pool_free++;
    obj_pool_used--;
    --
    1.7.9.6


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