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Date: Fri, 2 Sep 2016 11:51:58 -0400 (EDT)
From: CAI Qian <caiqian@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Al Viro <viro@...iv.linux.org.uk>,
Miklos Szeredi <miklos@...redi.hu>,
Rainer Weikusat <rweikusat@...eradapt.com>,
Hannes Frederic Sowa <hannes@...essinduktion.org>,
Rainer Weikusat <rweikusat@...ileactivedefense.com>,
Eric Sandeen <esandeen@...hat.com>,
Network Development <netdev@...r.kernel.org>
Subject: Re: possible circular locking dependency detected
----- Original Message -----
> From: "CAI Qian" <caiqian@...hat.com>
> To: "Linus Torvalds" <torvalds@...ux-foundation.org>
> Cc: "Al Viro" <viro@...iv.linux.org.uk>, "Miklos Szeredi" <miklos@...redi.hu>, "Rainer Weikusat"
> <rweikusat@...eradapt.com>, "Hannes Frederic Sowa" <hannes@...essinduktion.org>, "Rainer Weikusat"
> <rweikusat@...ileactivedefense.com>, "Eric Sandeen" <esandeen@...hat.com>, "Network Development"
> <netdev@...r.kernel.org>
> Sent: Friday, September 2, 2016 10:43:20 AM
> Subject: Re: possible circular locking dependency detected
>
>
>
> ----- Original Message -----
> > From: "Linus Torvalds" <torvalds@...ux-foundation.org>
> > To: "Al Viro" <viro@...iv.linux.org.uk>, "CAI Qian" <caiqian@...hat.com>
> > Cc: "Miklos Szeredi" <miklos@...redi.hu>, "Rainer Weikusat"
> > <rweikusat@...eradapt.com>, "Hannes Frederic Sowa"
> > <hannes@...essinduktion.org>, "Rainer Weikusat"
> > <rweikusat@...ileactivedefense.com>, "Eric Sandeen"
> > <esandeen@...hat.com>, "Network Development" <netdev@...r.kernel.org>
> > Sent: Thursday, September 1, 2016 6:04:38 PM
> > Subject: Re: possible circular locking dependency detected
> >
> > On Thu, Sep 1, 2016 at 2:43 PM, Linus Torvalds
> > <torvalds@...ux-foundation.org> wrote:
> > > On Thu, Sep 1, 2016 at 2:01 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> > >>
> > >> Outside as in "all fs activity in bind happens under it". Along with
> > >> assignment to ->u.addr, etc. IOW, make it the outermost lock there.
> > >
> > > Hah, yes. I misunderstood you.
> > >
> > > Yes. In fact that fixes the problem I mentioned, rather than introducing
> > > it.
> >
> > So the easiest approach would seem to be to revert commit c845acb324aa
> > ("af_unix: Fix splice-bind deadlock"), and then apply the lock split.
> >
> > Like the attached two patches.
> >
> > This is still *entirely* untested.
> Tested-by: CAI Qian <caiqian@...hat.com>
Actually, I took it back, and now spice seems start to deadlock using the reproducer,
https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/splice/splice01.c
[ 1749.956818]
[ 1749.958492] ======================================================
[ 1749.965386] [ INFO: possible circular locking dependency detected ]
[ 1749.972381] 4.8.0-rc4+ #34 Not tainted
[ 1749.976560] -------------------------------------------------------
[ 1749.983554] splice01/35921 is trying to acquire lock:
[ 1749.989188] (&sb->s_type->i_mutex_key#14){+.+.+.}, at: [<ffffffffa083c1f7>] xfs_file_buffered_aio_write+0x127/0x840 [xfs]
[ 1750.001644]
[ 1750.001644] but task is already holding lock:
[ 1750.008151] (&pipe->mutex/1){+.+.+.}, at: [<ffffffff8169e7c1>] pipe_lock+0x51/0x60
[ 1750.016753]
[ 1750.016753] which lock already depends on the new lock.
[ 1750.016753]
[ 1750.025880]
[ 1750.025880] the existing dependency chain (in reverse order) is:
[ 1750.034229]
-> #2 (&pipe->mutex/1){+.+.+.}:
[ 1750.039139] [<ffffffff812af52a>] lock_acquire+0x1fa/0x440
[ 1750.045857] [<ffffffff8266448d>] mutex_lock_nested+0xdd/0x850
[ 1750.052963] [<ffffffff8169e7c1>] pipe_lock+0x51/0x60
[ 1750.059190] [<ffffffff8171ee25>] splice_to_pipe+0x75/0x9e0
[ 1750.066001] [<ffffffff81723991>] __generic_file_splice_read+0xa71/0xe90
[ 1750.074071] [<ffffffff81723e71>] generic_file_splice_read+0xc1/0x1f0
[ 1750.081849] [<ffffffffa0838628>] xfs_file_splice_read+0x368/0x7b0 [xfs]
[ 1750.089940] [<ffffffff8171fa7e>] do_splice_to+0xee/0x150
[ 1750.096555] [<ffffffff817262f4>] SyS_splice+0x1144/0x1c10
[ 1750.103269] [<ffffffff81007b66>] do_syscall_64+0x1a6/0x500
[ 1750.110084] [<ffffffff8266ea7f>] return_from_SYSCALL_64+0x0/0x7a
[ 1750.117479]
-> #1 (&(&ip->i_iolock)->mr_lock#2){++++++}:
[ 1750.123649] [<ffffffff812af52a>] lock_acquire+0x1fa/0x440
[ 1750.130362] [<ffffffff8129b93e>] down_write_nested+0x5e/0xe0
[ 1750.137371] [<ffffffffa086772e>] xfs_ilock+0x2fe/0x550 [xfs]
[ 1750.144397] [<ffffffffa083c204>] xfs_file_buffered_aio_write+0x134/0x840 [xfs]
[ 1750.153175] [<ffffffffa083cb7d>] xfs_file_write_iter+0x26d/0x6d0 [xfs]
[ 1750.161177] [<ffffffff8168374e>] __vfs_write+0x2be/0x640
[ 1750.167799] [<ffffffff816876e2>] vfs_write+0x152/0x4b0
[ 1750.174220] [<ffffffff8168b0df>] SyS_write+0xdf/0x1d0
[ 1750.180547] [<ffffffff8266e9bc>] entry_SYSCALL_64_fastpath+0x1f/0xbd
[ 1750.188328]
-> #0 (&sb->s_type->i_mutex_key#14){+.+.+.}:
[ 1750.194508] [<ffffffff812adbc3>] __lock_acquire+0x3043/0x3dd0
[ 1750.201609] [<ffffffff812af52a>] lock_acquire+0x1fa/0x440
[ 1750.208321] [<ffffffff82668cda>] down_write+0x5a/0xe0
[ 1750.214645] [<ffffffffa083c1f7>] xfs_file_buffered_aio_write+0x127/0x840 [xfs]
[ 1750.223421] [<ffffffffa083cb7d>] xfs_file_write_iter+0x26d/0x6d0 [xfs]
[ 1750.231423] [<ffffffff816859be>] vfs_iter_write+0x29e/0x550
[ 1750.238330] [<ffffffff81722729>] iter_file_splice_write+0x529/0xb70
[ 1750.246012] [<ffffffff817258d4>] SyS_splice+0x724/0x1c10
[ 1750.252627] [<ffffffff81007b66>] do_syscall_64+0x1a6/0x500
[ 1750.259438] [<ffffffff8266ea7f>] return_from_SYSCALL_64+0x0/0x7a
[ 1750.266830]
[ 1750.266830] other info that might help us debug this:
[ 1750.266830]
[ 1750.275764] Chain exists of:
&sb->s_type->i_mutex_key#14 --> &(&ip->i_iolock)->mr_lock#2 --> &pipe->mutex/1
[ 1750.287213] Possible unsafe locking scenario:
[ 1750.287213]
[ 1750.293817] CPU0 CPU1
[ 1750.298871] ---- ----
[ 1750.303924] lock(&pipe->mutex/1);
[ 1750.307845] lock(&(&ip->i_iolock)->mr_lock#2);
[ 1750.315836] lock(&pipe->mutex/1);
[ 1750.322567] lock(&sb->s_type->i_mutex_key#14);
[ 1750.327748]
[ 1750.327748] *** DEADLOCK ***
[ 1750.327748]
[ 1750.334355] 2 locks held by splice01/35921:
[ 1750.339019] #0: (sb_writers#8){.+.+.+}, at: [<ffffffff8168f444>] __sb_start_write+0xb4/0xf0
[ 1750.348595] #1: (&pipe->mutex/1){+.+.+.}, at: [<ffffffff8169e7c1>] pipe_lock+0x51/0x60
[ 1750.357686]
[ 1750.357686] stack backtrace:
[ 1750.362548] CPU: 50 PID: 35921 Comm: splice01 Not tainted 4.8.0-rc4+ #34
[ 1750.370026] Hardware name: Intel Corporation S2600WTT/S2600WTT, BIOS GRNDSDP1.86B.0044.R00.1501191641 01/19/2015
[ 1750.381382] 0000000000000000 000000003bca9477 ffff88044c4176e0 ffffffff81a3d191
[ 1750.389675] ffffffff84292880 ffffffff842b9e30 ffff88044c417730 ffffffff812a6aa6
[ 1750.397968] ffffffff84292880 ffff880414a28cd0 ffff88044c417850 ffff880414a28cd0
[ 1750.406261] Call Trace:
[ 1750.408992] [<ffffffff81a3d191>] dump_stack+0x85/0xc4
[ 1750.414725] [<ffffffff812a6aa6>] print_circular_bug+0x356/0x460
[ 1750.421428] [<ffffffff812adbc3>] __lock_acquire+0x3043/0x3dd0
[ 1750.427942] [<ffffffff81414fe9>] ? is_ftrace_trampoline+0x99/0xe0
[ 1750.434840] [<ffffffff812aab80>] ? debug_check_no_locks_freed+0x2c0/0x2c0
[ 1750.442512] [<ffffffff812a0272>] ? add_lock_to_list.isra.29.constprop.45+0x142/0x1d0
[ 1750.451249] [<ffffffff812acd9e>] ? __lock_acquire+0x221e/0x3dd0
[ 1750.457952] [<ffffffff812aa3ce>] ? trace_hardirqs_on_caller+0x3fe/0x580
[ 1750.465430] [<ffffffff812af52a>] lock_acquire+0x1fa/0x440
[ 1750.471578] [<ffffffffa083c1f7>] ? xfs_file_buffered_aio_write+0x127/0x840 [xfs]
[ 1750.479929] [<ffffffff82668cda>] down_write+0x5a/0xe0
[ 1750.485691] [<ffffffffa083c1f7>] ? xfs_file_buffered_aio_write+0x127/0x840 [xfs]
[ 1750.494070] [<ffffffffa083c1f7>] xfs_file_buffered_aio_write+0x127/0x840 [xfs]
[ 1750.502226] [<ffffffff81007b66>] ? do_syscall_64+0x1a6/0x500
[ 1750.508666] [<ffffffffa083c0d0>] ? xfs_file_dio_aio_write+0xca0/0xca0 [xfs]
[ 1750.516532] [<ffffffff812a9f72>] ? mark_held_locks+0xd2/0x130
[ 1750.523044] [<ffffffff812f5887>] ? debug_lockdep_rcu_enabled+0x77/0x90
[ 1750.530417] [<ffffffff82664873>] ? mutex_lock_nested+0x4c3/0x850
[ 1750.537243] [<ffffffffa083cb7d>] xfs_file_write_iter+0x26d/0x6d0 [xfs]
[ 1750.544625] [<ffffffff8169e7c1>] ? pipe_lock+0x51/0x60
[ 1750.550456] [<ffffffff816859be>] vfs_iter_write+0x29e/0x550
[ 1750.556770] [<ffffffff81685720>] ? vfs_iter_read+0x540/0x540
[ 1750.563181] [<ffffffff81722729>] iter_file_splice_write+0x529/0xb70
[ 1750.570271] [<ffffffff81722200>] ? page_cache_pipe_buf_confirm+0x1f0/0x1f0
[ 1750.578041] [<ffffffff812f5a33>] ? rcu_read_lock_sched_held+0xa3/0x120
[ 1750.585423] [<ffffffff812f6055>] ? rcu_sync_lockdep_assert+0x75/0xb0
[ 1750.592609] [<ffffffff8129bd6c>] ? percpu_down_read+0x5c/0xa0
[ 1750.599118] [<ffffffff8168f444>] ? __sb_start_write+0xb4/0xf0
[ 1750.605627] [<ffffffff817258d4>] SyS_splice+0x724/0x1c10
[ 1750.611651] [<ffffffff812f5a33>] ? rcu_read_lock_sched_held+0xa3/0x120
[ 1750.619033] [<ffffffff817251b0>] ? compat_SyS_vmsplice+0x1f0/0x1f0
[ 1750.626025] [<ffffffff81007a12>] ? do_syscall_64+0x52/0x500
[ 1750.632338] [<ffffffff817251b0>] ? compat_SyS_vmsplice+0x1f0/0x1f0
[ 1750.639330] [<ffffffff81007b66>] do_syscall_64+0x1a6/0x500
[ 1750.645549] [<ffffffff8100401a>] ? trace_hardirqs_on_thunk+0x1a/0x1c
[ 1750.652737] [<ffffffff8266ea7f>] entry_SYSCALL64_slow_path+0x25/0x25
> >
> > Rainer?
> >
> > Linus
> >
>
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