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Date: Wed, 27 Nov 2013 20:11:28 -0800
From: Greg KH <gregkh@...uxfoundation.org>
To: Xiaotian Feng <xtfeng@...il.com>
Cc: Tejun Heo <tj@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>, neilb@...e.de,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: page fault deadlock
On Thu, Nov 28, 2013 at 11:25:32AM +0800, Xiaotian Feng wrote:
> Hi,
>
> When I upgrade to latest kernel, I found my system hang there. It
> is reproducible on my virtualbox, and I found each time I mounted my
> RAID6 partition and tried to vi or build kernel, my whole system
> lockup very soon.
>
> After turning on lockdep, I found following lockdep warning:
>
> [ 27.848462]
> [ 27.848471] ======================================================
> [ 27.848477] [ INFO: possible circular locking dependency detected ]
> [ 27.848484] 3.13.0-rc1+ #1 Tainted: GF W
> [ 27.848490] -------------------------------------------------------
> [ 27.848496] Xorg/1268 is trying to acquire lock:
> [ 27.848501] (&of->mutex){+.+.+.}, at: [<ffffffff8125d58f>]
> sysfs_bin_mmap+0x4f/0x120
> [ 27.848516]
> [ 27.848516] but task is already holding lock:
> [ 27.848521] (&mm->mmap_sem){++++++}, at: [<ffffffff811875bf>]
> vm_mmap_pgoff+0x6f/0xc0
> [ 27.848534]
> [ 27.848534] which lock already depends on the new lock.
> [ 27.848534]
> [ 27.848541]
> [ 27.848541] the existing dependency chain (in reverse order) is:
> [ 27.848547]
> [ 27.848547] -> #2 (&mm->mmap_sem){++++++}:
> [ 27.848556] [<ffffffff810c0510>] lock_acquire+0xb0/0x160
> [ 27.848564] [<ffffffff8119177c>] might_fault+0x8c/0xb0
> [ 27.848572] [<ffffffff815f4c08>] md_ioctl+0xa78/0x19b0
> [ 27.848580] [<ffffffff813915a4>] blkdev_ioctl+0x234/0x840
> [ 27.848588] [<ffffffff8121db61>] block_ioctl+0x41/0x50
> [ 27.848597] [<ffffffff811f5330>] do_vfs_ioctl+0x300/0x520
> [ 27.848605] [<ffffffff811f55d1>] SyS_ioctl+0x81/0xa0
> [ 27.848613] [<ffffffff81784e98>] tracesys+0xe1/0xe6
> [ 27.848622]
> [ 27.848622] -> #1 (&mddev->reconfig_mutex){+.+.+.}:
> [ 27.848630] [<ffffffff810c0510>] lock_acquire+0xb0/0x160
> [ 27.848637] [<ffffffff81778568>]
> mutex_lock_interruptible_nested+0x78/0x610
> [ 27.848646] [<ffffffff815e9750>] rdev_attr_show+0x40/0x90
> [ 27.848654] [<ffffffff8125db2a>] sysfs_seq_show+0xda/0x170
> [ 27.848662] [<ffffffff812076f4>] seq_read+0x164/0x3e0
> [ 27.848671] [<ffffffff811e1005>] vfs_read+0x95/0x160
> [ 27.848680] [<ffffffff811e1b19>] SyS_read+0x49/0xa0
> [ 27.848687] [<ffffffff81784e98>] tracesys+0xe1/0xe6
> [ 27.848695]
> [ 27.848695] -> #0 (&of->mutex){+.+.+.}:
> [ 27.848703] [<ffffffff810bfd47>] __lock_acquire+0x1587/0x1ca0
> [ 27.848711] [<ffffffff810c0510>] lock_acquire+0xb0/0x160
> [ 27.848718] [<ffffffff81778048>] mutex_lock_nested+0x68/0x510
> [ 27.848725] [<ffffffff8125d58f>] sysfs_bin_mmap+0x4f/0x120
> [ 27.848732] [<ffffffff8119d82d>] mmap_region+0x3ed/0x5d0
> [ 27.848741] [<ffffffff8119dd5e>] do_mmap_pgoff+0x34e/0x3d0
> [ 27.848748] [<ffffffff811875e0>] vm_mmap_pgoff+0x90/0xc0
> [ 27.848755] [<ffffffff8119c2b5>] SyS_mmap_pgoff+0x1d5/0x270
> [ 27.848763] [<ffffffff8101ae52>] SyS_mmap+0x22/0x30
> [ 27.848771] [<ffffffff81784e98>] tracesys+0xe1/0xe6
> [ 27.848778]
> [ 27.848778] other info that might help us debug this:
> [ 27.848778]
> [ 27.848785] Chain exists of:
> [ 27.848785] &of->mutex --> &mddev->reconfig_mutex --> &mm->mmap_sem
> [ 27.848785]
> [ 27.848795] Possible unsafe locking scenario:
> [ 27.848795]
> [ 27.848800] CPU0 CPU1
> [ 27.848805] ---- ----
> [ 27.848810] lock(&mm->mmap_sem);
> [ 27.848817] lock(&mddev->reconfig_mutex);
> [ 27.848824] lock(&mm->mmap_sem);
> [ 27.848830] lock(&of->mutex);
> [ 27.848837]
> [ 27.848837] *** DEADLOCK ***
> [ 27.848837]
> [ 27.848844] 1 lock held by Xorg/1268:
> [ 27.848849] #0: (&mm->mmap_sem){++++++}, at: [<ffffffff811875bf>]
> vm_mmap_pgoff+0x6f/0xc0
> [ 27.848861]
> [ 27.848861] stack backtrace:
> [ 27.848868] CPU: 1 PID: 1268 Comm: Xorg Tainted: GF W 3.13.0-rc1+ #1
> [ 27.848873] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS
> VirtualBox 12/01/2006
> [ 27.848879] ffffffff822daa00 ffff8800d0371bc8 ffffffff817725f7
> ffffffff822cbdc0
> [ 27.848901] ffff8800d0371c08 ffffffff8176d9eb ffff8800d0371c60
> ffff880115b42a78
> [ 27.848909] 0000000000000000 ffff880115b42a78 ffff880115b422a0
> 0000000000000001
> [ 27.848918] Call Trace:
> [ 27.848930] [<ffffffff817725f7>] dump_stack+0x4e/0x7a
> [ 27.848942] [<ffffffff8176d9eb>] print_circular_bug+0x1f9/0x208
> [ 27.848952] [<ffffffff810bfd47>] __lock_acquire+0x1587/0x1ca0
> [ 27.848964] [<ffffffff8101955f>] ? print_context_stack+0x8f/0x100
> [ 27.848975] [<ffffffff810c0510>] lock_acquire+0xb0/0x160
> [ 27.848986] [<ffffffff8125d58f>] ? sysfs_bin_mmap+0x4f/0x120
> [ 27.848996] [<ffffffff8125d58f>] ? sysfs_bin_mmap+0x4f/0x120
> [ 27.849007] [<ffffffff81778048>] mutex_lock_nested+0x68/0x510
> [ 27.849016] [<ffffffff8125d58f>] ? sysfs_bin_mmap+0x4f/0x120
> [ 27.849027] [<ffffffff8176456e>] ? kmemleak_alloc+0x4e/0xb0
> [ 27.849038] [<ffffffff8125d58f>] sysfs_bin_mmap+0x4f/0x120
> [ 27.849048] [<ffffffff8119d82d>] mmap_region+0x3ed/0x5d0
> [ 27.849058] [<ffffffff8119dd5e>] do_mmap_pgoff+0x34e/0x3d0
> [ 27.849070] [<ffffffff811875e0>] vm_mmap_pgoff+0x90/0xc0
> [ 27.849080] [<ffffffff8119c2b5>] SyS_mmap_pgoff+0x1d5/0x270
> [ 27.849092] [<ffffffff81023c55>] ? syscall_trace_enter+0x145/0x270
> [ 27.849102] [<ffffffff8101ae52>] SyS_mmap+0x22/0x30
> [ 27.849112] [<ffffffff81784e98>] tracesys+0xe1/0xe6
>
>
> I think it is a real deadlock, and it is caused by commit
> 3124eb1679b28726 "sysfs: merge regular and bin file handling".
>
> With that commit, sysfs_bin_mmap will hold of->mutex.
>
> So assume cpu0 called sysfs_bin_mmap, acquired mmap_sem and trying
> to get of->mutex.
>
> CPU1 called sysfs_seq_show, acqured of->mutex and trying to
> get mddev->reconfig_mutex.
>
> CPU2 called md_ioctl, acquired mddev->reconfig_mutex, and
> later call copy_from_user and page fault trying to get mmap_sem.
>
> DEADLOCK now. I can't test the effort of reverting 3124eb16 as
> there're a whole patchset and many commits after that. But I do
> believe it's buggy and the root cause of my system hang.
>
> CPU0: CPU1:
> CPU2:
> lock(&mm->mmap_sem)
> lock(&of->mutex);
>
> lock(&mddev->reconfig_mutex)
>
> lock(&mm->mmap_sem)
>
> lock(&mddev->reconfig_mutex)
> lock(&of->mutex)
>
> Can we revert commit 3124eb167? or any patches to solve this page
> fault deadlock? Thanks.
Can you try linux-next, this should be fixed with a patch in my tree
there, thanks.
greg k-h
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