Message-ID: <707391732.1338517.1472834792099.JavaMail.zimbra@redhat.com>
Date:   Fri, 2 Sep 2016 12:46:32 -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 11:51:58 AM
> 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>
OK, this tag still stand. The below issue is also reproduced without those
patches, so a separate problem most likely was introduced recently (after
rc3 or rc4) by probably some xfs update.
   CAI Qian 
> 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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