block: don't call blk_drain_queue() if elevator is not up
blk_cleanup_queue() may be called before elevator is set up on a queue which triggers the following oops. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [<ffffffff8125a69c>] elv_drain_elevator+0x1c/0x70 ... Pid: 830, comm: kworker/0:2 Not tainted 3.1.0-next-20111025_64+ #1590 Bochs Bochs RIP: 0010:[<ffffffff8125a69c>] [<ffffffff8125a69c>] elv_drain_elevator+0x1c/0x70 ... Call Trace: [<ffffffff8125da92>] blk_drain_queue+0x42/0x70 [<ffffffff8125db90>] blk_cleanup_queue+0xd0/0x1c0 [<ffffffff81469640>] md_free+0x50/0x70 [<ffffffff8126f43b>] kobject_release+0x8b/0x1d0 [<ffffffff81270d56>] kref_put+0x36/0xa0 [<ffffffff8126f2b7>] kobject_put+0x27/0x60 [<ffffffff814693af>] mddev_delayed_delete+0x2f/0x40 [<ffffffff81083450>] process_one_work+0x100/0x3b0 [<ffffffff8108527f>] worker_thread+0x15f/0x3a0 [<ffffffff81089937>] kthread+0x87/0x90 [<ffffffff81621834>] kernel_thread_helper+0x4/0x10 Fix it by making blk_cleanup_queue() check whether q->elevator is set up before invoking blk_drain_queue. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-and-tested-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -407,8 +407,13 @@ void blk_cleanup_queue(struct request_queue *q)
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spin_unlock_irq(lock);
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mutex_unlock(&q->sysfs_lock);
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/* drain all requests queued before DEAD marking */
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blk_drain_queue(q, true);
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/*
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* Drain all requests queued before DEAD marking. The caller might
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* be trying to tear down @q before its elevator is initialized, in
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* which case we don't want to call into draining.
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*/
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if (q->elevator)
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blk_drain_queue(q, true);
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/* @q won't process any more request, flush async actions */
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del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
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