Messages in this thread | | | Date | Thu, 3 Sep 2009 14:28:36 -0700 | From | Andrew Morton <> | Subject | Re: [mmotm][BUG] lockdep warning block I/O (Was Re: mmotm 2009-08-27-16-51 uploaded |
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On Tue, 1 Sep 2009 18:07:17 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > Here is mmont-Aug27's lockdep wanring. This was printed out when oom-kill happens. > I'm sorry if already fixed.
My life's project is to hunt down the guy who invented mail client wordwrapping, set him on fire then dance on his ashes.
> = > Sep 1 18:01:16 localhost kernel: [ 3012.503035] ====================================================== > Sep 1 18:01:16 localhost kernel: [ 3012.503039] [ INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected ] > Sep 1 18:01:16 localhost kernel: [ 3012.503042] 2.6.31-rc7-mm1 #3 > Sep 1 18:01:16 localhost kernel: [ 3012.503049] ------------------------------------------------------ > Sep 1 18:01:16 localhost kernel: [ 3012.503052] kblockd/7/350 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: > Sep 1 18:01:16 localhost kernel: [ 3012.503058] (bdev_lock){+.+...}, at: [<ffffffff811458c7>] nr_blockdev_pages+0x1 > 7/0x80 > Sep 1 18:01:16 localhost kernel: [ 3012.503069] > Sep 1 18:01:16 localhost kernel: [ 3012.503070] and this task is already holding: > Sep 1 18:01:16 localhost kernel: [ 3012.503075] (&q->__queue_lock){..-.-.}, at: [<ffffffff811e9ff8>] cfq_kick_queue > +0x28/0x50 > Sep 1 18:01:16 localhost kernel: [ 3012.503083] which would create a new lock dependency: > Sep 1 18:01:16 localhost kernel: [ 3012.503087] (&q->__queue_lock){..-.-.} -> (bdev_lock){+.+...} > Sep 1 18:01:16 localhost kernel: [ 3012.503100]
I'd say the core problem here is that __alloc_pages_slowpath() is calling show_mem(). Because show_mem() is a "high level" function which takes "high level" locks. ie: bdev_lock.
It's inappropriate that alloc_pages() is assuming that it is safe to call show_mem() from all contexts in which alloc_pages() might be called.
That show_mem() call has been there since 2005, so I don't know what caused this to be revealed now.
It's not at all a serious bug and the chances of us deadlocking the kernel here are close to zero. An appropriate fix would be to replace that show_mem() call with something which can be safely called from all contexts in which the page allocator can be called.
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