On Fri, 2015-11-06 at 13:58 +0100, Dmitry Vyukov wrote:
> Hello,
>
> I am on revision d1e41ff11941784f469f17795a4d9425c2eb4b7a (Nov 5) and
> seeing the following lockdep reports. I don't have exact reproducer
> program as it is caused by several independent programs (state
> accumulated in kernel across invocations); if the report is not enough
> I can try to cook a reproducer.
>
> Thanks.
>
> [ INFO: possible circular locking dependency detected ]
> 4.3.0+ #30 Not tainted
> -------------------------------------------------------
> a.out/9972 is trying to acquire lock:
> (&pipe->mutex/1){+.+.+.}, at: [< inline >] pipe_lock_nested
> fs/pipe.c:59
> (&pipe->mutex/1){+.+.+.}, at: [<ffffffff814d6e46>]
> pipe_lock+0x56/0x70 fs/pipe.c:67
>
> but task is already holding lock:
> (sb_writers#5){.+.+.+}, at: [<ffffffff814c77ec>]
> __sb_start_write+0xec/0x130 fs/super.c:1198
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #2 (sb_writers#5){.+.+.+}:
> [<ffffffff811f655d>] lock_acquire+0x16d/0x2f0
> kernel/locking/lockdep.c:3585
> [<ffffffff811e434c>] percpu_down_read+0x3c/0xa0
> kernel/locking/percpu-rwsem.c:73
> [<ffffffff814c77ec>] __sb_start_write+0xec/0x130 fs/super.c:1198
> [< inline >] sb_start_write include/linux/fs.h:1449
> [<ffffffff81526f4f>] mnt_want_write+0x3f/0xb0 fs/namespace.c:386
> [<ffffffff814f43f6>] filename_create+0x106/0x450 fs/namei.c:3425
> [<ffffffff814f4773>] kern_path_create+0x33/0x40 fs/namei.c:3471
> [< inline >] unix_mknod net/unix/af_unix.c:849
> [<ffffffff82acb27b>] unix_bind+0x41b/0xa10 net/unix/af_unix.c:917
> [<ffffffff827636da>] SYSC_bind+0x1ea/0x250 net/socket.c:1383
> [<ffffffff82766164>] SyS_bind+0x24/0x30 net/socket.c:1369
> [<ffffffff82f21951>] entry_SYSCALL_64_fastpath+0x31/0x9a
> arch/x86/entry/entry_64.S:187
>
> -> #1 (&u->readlock){+.+.+.}:
> [<ffffffff811f655d>] lock_acquire+0x16d/0x2f0
> kernel/locking/lockdep.c:3585
> [< inline >] __mutex_lock_common kernel/locking/mutex.c:518
> [<ffffffff82f196c9>] mutex_lock_interruptible_nested+0xa9/0xa30
> kernel/locking/mutex.c:647
> [<ffffffff82ac32bc>] unix_stream_sendpage+0x23c/0x700
> net/unix/af_unix.c:1768
> [<ffffffff82761690>] kernel_sendpage+0x90/0xe0 net/socket.c:3278
> [<ffffffff82761785>] sock_sendpage+0xa5/0xd0 net/socket.c:765
> [<ffffffff8155668a>] pipe_to_sendpage+0x26a/0x320 fs/splice.c:720
> [< inline >] splice_from_pipe_feed fs/splice.c:772
> [<ffffffff815579a8>] __splice_from_pipe+0x268/0x740 fs/splice.c:889
> [<ffffffff8155c2f7>] splice_from_pipe+0xf7/0x140 fs/splice.c:924
> [<ffffffff8155c380>] generic_splice_sendpage+0x40/0x50 fs/splice.c:1097
> [< inline >] do_splice_from fs/splice.c:1116
> [< inline >] do_splice fs/splice.c:1392
> [< inline >] SYSC_splice fs/splice.c:1695
> [<ffffffff8155d005>] SyS_splice+0x845/0x17c0 fs/splice.c:1678
> [<ffffffff82f21951>] entry_SYSCALL_64_fastpath+0x31/0x9a
> arch/x86/entry/entry_64.S:187
>
> -> #0 (&pipe->mutex/1){+.+.+.}:
> [< inline >] check_prev_add kernel/locking/lockdep.c:1853
> [< inline >] check_prevs_add kernel/locking/lockdep.c:1958
> [< inline >] validate_chain kernel/locking/lockdep.c:2144
> [<ffffffff811f3769>] __lock_acquire+0x36d9/0x40e0
> kernel/locking/lockdep.c:3206
> [<ffffffff811f655d>] lock_acquire+0x16d/0x2f0
> kernel/locking/lockdep.c:3585
> [< inline >] __mutex_lock_common kernel/locking/mutex.c:518
> [<ffffffff82f18dcc>] mutex_lock_nested+0x9c/0x8f0
> kernel/locking/mutex.c:618
> [< inline >] pipe_lock_nested fs/pipe.c:59
> [<ffffffff814d6e46>] pipe_lock+0x56/0x70 fs/pipe.c:67
> [<ffffffff815581c9>] iter_file_splice_write+0x199/0xb20 fs/splice.c:962
> [< inline >] do_splice_from fs/splice.c:1116
> [< inline >] do_splice fs/splice.c:1392
> [< inline >] SYSC_splice fs/splice.c:1695
> [<ffffffff8155d005>] SyS_splice+0x845/0x17c0 fs/splice.c:1678
> [<ffffffff82f21951>] entry_SYSCALL_64_fastpath+0x31/0x9a
> arch/x86/entry/entry_64.S:187
>
> other info that might help us debug this:
>
> Chain exists of:
> &pipe->mutex/1 --> &u->readlock --> sb_writers#5
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(sb_writers#5);
> lock(&u->readlock);
> lock(sb_writers#5);
> lock(&pipe->mutex/1);
>
> *** DEADLOCK ***
>
> 1 lock held by a.out/9972:
> #0: (sb_writers#5){.+.+.+}, at: [<ffffffff814c77ec>]
> __sb_start_write+0xec/0x130 fs/super.c:1198
>
> stack backtrace:
> CPU: 1 PID: 9972 Comm: a.out Not tainted 4.3.0+ #30
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> 00000000ffffffff ffff88003d777938 ffffffff81aad406 ffffffff846046a0
> ffffffff84606860 ffffffff846086c0 ffff88003d777980 ffffffff811ec511
> ffff88003d777a80 000000003cf79640 ffff88003cf79df0 ffff88003cf79e12
> Call Trace:
> [< inline >] __dump_stack lib/dump_stack.c:15
> [<ffffffff81aad406>] dump_stack+0x68/0x92 lib/dump_stack.c:50
> [<ffffffff811ec511>] print_circular_bug+0x2d1/0x390
> kernel/locking/lockdep.c:1226
> [< inline >] check_prev_add kernel/locking/lockdep.c:1853
> [< inline >] check_prevs_add kernel/locking/lockdep.c:1958
> [< inline >] validate_chain kernel/locking/lockdep.c:2144
> [<ffffffff811f3769>] __lock_acquire+0x36d9/0x40e0 kernel/locking/lockdep.c:3206
> [<ffffffff811f655d>] lock_acquire+0x16d/0x2f0 kernel/locking/lockdep.c:3585
> [< inline >] __mutex_lock_common kernel/locking/mutex.c:518
> [<ffffffff82f18dcc>] mutex_lock_nested+0x9c/0x8f0 kernel/locking/mutex.c:618
> [< inline >] pipe_lock_nested fs/pipe.c:59
> [<ffffffff814d6e46>] pipe_lock+0x56/0x70 fs/pipe.c:67
> [<ffffffff815581c9>] iter_file_splice_write+0x199/0xb20 fs/splice.c:962
> [< inline >] do_splice_from fs/splice.c:1116
> [< inline >] do_splice fs/splice.c:1392
> [< inline >] SYSC_splice fs/splice.c:1695
> [<ffffffff8155d005>] SyS_splice+0x845/0x17c0 fs/splice.c:1678
> [<ffffffff82f21951>] entry_SYSCALL_64_fastpath+0x31/0x9a
> arch/x86/entry/entry_64.S:187
> --
Thank you for this report.
pipe is part of fs, not net ;)
CC Al Viro.
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