Messages in this thread Patch in this message | | | Subject | Re: lockdep vs rmmod loop | From | Peter Zijlstra <> | Date | Thu, 16 Oct 2008 13:49:06 +0200 |
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On Tue, 2008-10-14 at 19:14 +0400, Alexey Dobriyan wrote: > On Tue, Oct 14, 2008 at 01:51:38PM +0200, Peter Zijlstra wrote: > > On Mon, 2008-10-13 at 21:57 +0400, Alexey Dobriyan wrote: > > > This exists for quite some time, IIRC. > > > > > > # rmmod loop > > > > I tried to reproduce with -git from today but failed. > > > > v2.6.27-3976-g7591103 > > > > I build a x86_64 kernel with modular loop and lockdep enabled, then I > > did: modprobe loop; rmmod loop > > > > Is there anything else to reproducing this? > > No, modprobe,rmmod is enough here even with minimal debugging.
Yep can reproduce with your config.
Its:
static void wait_on_work(struct work_struct *work) { ... lock_map_acquire(&work->lockdep_map); lock_map_release(&work->lockdep_map);
that triggers this. Which would suggest the work-let wasn't properly initialized. Now on to figuring out where it came from.
Loop doesn't appear to have anything workqueue related in it, which suggests the block layer.
And indeed, it appears blk_queue_make_request() initializes q->unplug_work, and by modprobe loop; rmmod loop you never get to run that, therefore q->unplug_work gets canceled without ever having been initialized -> bang!
And indeed, the below patch fixes it:
--- Subject: block: move q->unplug_work initialization From: Peter Zijlstra <a.p.zijlstra@chello.nl> Date: Thu Oct 16 13:44:57 CEST 2008
modprobe loop; rmmod loop effectively creates a blk_queue and destroys it which results in q->unplug_work being canceled without it ever being initialized.
Therefore, move the initialization of q->unplug_work from blk_queue_make_request() to blk_alloc_queue*().
Reported-by: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- block/blk-core.c | 1 + block/blk-settings.c | 2 -- 2 files changed, 1 insertion(+), 2 deletions(-)
Index: linux-2.6/block/blk-core.c =================================================================== --- linux-2.6.orig/block/blk-core.c +++ linux-2.6/block/blk-core.c @@ -501,6 +501,7 @@ struct request_queue *blk_alloc_queue_no init_timer(&q->unplug_timer); setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q); INIT_LIST_HEAD(&q->timeout_list); + INIT_WORK(&q->unplug_work, blk_unplug_work); kobject_init(&q->kobj, &blk_queue_ktype); Index: linux-2.6/block/blk-settings.c =================================================================== --- linux-2.6.orig/block/blk-settings.c +++ linux-2.6/block/blk-settings.c @@ -141,8 +141,6 @@ void blk_queue_make_request(struct reque if (q->unplug_delay == 0) q->unplug_delay = 1; - INIT_WORK(&q->unplug_work, blk_unplug_work); - q->unplug_timer.function = blk_unplug_timeout; q->unplug_timer.data = (unsigned long)q;
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