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Subjectlockdep trace from kill_fasync (tty) vs account (random)
Came home to this on my box that I left fuzz-testing.

[56194.899379] ======================================================
[56194.899529] [ INFO: possible circular locking dependency detected ]
[56194.899679] 3.9.0-rc1+ #67 Not tainted
[56194.899769] -------------------------------------------------------
[56194.899920] modprobe/14420 is trying to acquire lock:
[56194.900041] blocked: (&(&new->fa_lock)->rlock){......}, instance: ffff8800c240b4b8, at: [<ffffffff811c31d6>] kill_fasync+0x96/0x2a0
[56194.900343]
but task is already holding lock:
[56194.900478] held: (nonblocking_pool.lock){..-...}, instance: ffffffff81ca99a0, at: [<ffffffff81417909>] account+0x39/0x1c0
[56194.900765]
which lock already depends on the new lock.

[56194.900949]
the existing dependency chain (in reverse order) is:
[56194.901123]
-> #2 (nonblocking_pool.lock){..-...}:
[56194.901249] [<ffffffff810b7b72>] lock_acquire+0x92/0x1d0
[56194.901396] [<ffffffff816c48f3>] _raw_spin_lock_irqsave+0x53/0x90
[56194.901555] [<ffffffff814180c4>] mix_pool_bytes.constprop.16+0x44/0x180
[56194.901733] [<ffffffff8141848b>] add_device_randomness+0x6b/0x90
[56194.901895] [<ffffffff810725c2>] posix_cpu_timers_exit+0x22/0x50
[56194.902057] [<ffffffff81048eff>] release_task+0x13f/0x670
[56194.902200] [<ffffffff8104b16f>] do_exit+0x6af/0xce0
[56194.902335] [<ffffffff810c406e>] __module_put_and_exit+0x1e/0x20
[56194.902495] [<ffffffff812f9177>] cryptomgr_test+0x37/0x50
[56194.902641] [<ffffffff8107071d>] kthread+0xed/0x100
[56194.902768] [<ffffffff816cd5dc>] ret_from_fork+0x7c/0xb0
[56194.909181]
-> #1 (&(&sighand->siglock)->rlock){-.-...}:
[56194.921863] [<ffffffff810b7b72>] lock_acquire+0x92/0x1d0
[56194.928381] [<ffffffff816c4da7>] _raw_write_lock_irq+0x47/0x80
[56194.934903] [<ffffffff811c22ab>] __f_setown+0x6b/0x100
[56194.941244] [<ffffffff813eed68>] __tty_fasync+0xd8/0x160
[56194.947564] [<ffffffff813eee30>] tty_fasync+0x40/0x60
[56194.953794] [<ffffffff811c43e2>] do_vfs_ioctl+0x3d2/0x570
[56194.959981] [<ffffffff811c4611>] sys_ioctl+0x91/0xb0
[56194.966155] [<ffffffff816cd682>] system_call_fastpath+0x16/0x1b
[56194.972304]
-> #0 (&(&new->fa_lock)->rlock){......}:
[56194.984490] [<ffffffff810b73f6>] __lock_acquire+0x1b86/0x1c80
[56194.990754] [<ffffffff810b7b72>] lock_acquire+0x92/0x1d0
[56194.996950] [<ffffffff816c48f3>] _raw_spin_lock_irqsave+0x53/0x90
[56195.003199] [<ffffffff811c31d6>] kill_fasync+0x96/0x2a0
[56195.009468] [<ffffffff814179db>] account+0x10b/0x1c0
[56195.015755] [<ffffffff81418ad0>] extract_entropy+0x80/0x340
[56195.022035] [<ffffffff81418f50>] get_random_bytes+0x20/0x30
[56195.028289] [<ffffffff8120e172>] load_elf_binary+0xb82/0x1af0
[56195.034583] [<ffffffff811b818b>] search_binary_handler+0x1ab/0x500
[56195.040856] [<ffffffff811b8f55>] do_execve_common.isra.26+0x645/0x710
[56195.047172] [<ffffffff811b9038>] do_execve+0x18/0x20
[56195.053373] [<ffffffff81065a80>] ____call_usermodehelper+0xf0/0x120
[56195.059589] [<ffffffff816cd5dc>] ret_from_fork+0x7c/0xb0
[56195.065737]
other info that might help us debug this:

[56195.083945] Chain exists of:
&(&new->fa_lock)->rlock --> &(&sighand->siglock)->rlock --> nonblocking_pool.lock

[56195.102332] Possible unsafe locking scenario:

[56195.114608] CPU0 CPU1
[56195.120611] ---- ----
[56195.126579] lock(nonblocking_pool.lock);
[56195.132476] lock(&(&sighand->siglock)->rlock);
[56195.138528] lock(nonblocking_pool.lock);
[56195.144492] lock(&(&new->fa_lock)->rlock);
[56195.150410]
*** DEADLOCK ***

[56195.167408] 2 locks on stack by modprobe/14420:
[56195.172807] #0: held: (nonblocking_pool.lock){..-...}, instance: ffffffff81ca99a0, at: [<ffffffff81417909>] account+0x39/0x1c0
[56195.178598] #1: blocked: (rcu_read_lock){.+.+..}, instance: ffffffff81c39920, at: [<ffffffff811c3161>] kill_fasync+0x21/0x2a0
[56195.184418]
stack backtrace:
[56195.195499] Pid: 14420, comm: modprobe Not tainted 3.9.0-rc1+ #67
[56195.201091] Call Trace:
[56195.206749] [<ffffffff816b9325>] print_circular_bug+0x1fe/0x20f
[56195.212492] [<ffffffff810b73f6>] __lock_acquire+0x1b86/0x1c80
[56195.218220] [<ffffffff810b5b75>] ? __lock_acquire+0x305/0x1c80
[56195.223941] [<ffffffff8100a196>] ? native_sched_clock+0x26/0x90
[56195.229611] [<ffffffff810b7b72>] lock_acquire+0x92/0x1d0
[56195.235278] [<ffffffff811c31d6>] ? kill_fasync+0x96/0x2a0
[56195.240916] [<ffffffff816c48f3>] _raw_spin_lock_irqsave+0x53/0x90
[56195.246558] [<ffffffff811c31d6>] ? kill_fasync+0x96/0x2a0
[56195.252203] [<ffffffff811c31d6>] kill_fasync+0x96/0x2a0
[56195.257818] [<ffffffff811c3161>] ? kill_fasync+0x21/0x2a0
[56195.263471] [<ffffffff814179db>] account+0x10b/0x1c0
[56195.269081] [<ffffffff810b8675>] ? trace_hardirqs_on_caller+0x115/0x1a0
[56195.274765] [<ffffffff81418ad0>] extract_entropy+0x80/0x340
[56195.280404] [<ffffffff81089173>] ? local_clock+0x43/0x50
[56195.286021] [<ffffffff816c5860>] ? retint_restore_args+0xe/0xe
[56195.291684] [<ffffffff81418f50>] get_random_bytes+0x20/0x30
[56195.297292] [<ffffffff8120e172>] load_elf_binary+0xb82/0x1af0
[56195.302854] [<ffffffff8120d5f0>] ? load_elf_library+0x220/0x220
[56195.308435] [<ffffffff8120d5f0>] ? load_elf_library+0x220/0x220
[56195.313975] [<ffffffff811b818b>] search_binary_handler+0x1ab/0x500
[56195.319495] [<ffffffff811b805f>] ? search_binary_handler+0x7f/0x500
[56195.325056] [<ffffffff811b8f55>] do_execve_common.isra.26+0x645/0x710
[56195.330671] [<ffffffff811b8a32>] ? do_execve_common.isra.26+0x122/0x710
[56195.336307] [<ffffffff811b9038>] do_execve+0x18/0x20
[56195.341907] [<ffffffff81065a80>] ____call_usermodehelper+0xf0/0x120
[56195.347486] [<ffffffff810832f0>] ? schedule_tail+0x30/0xb0
[56195.353073] [<ffffffff81065990>] ? proc_cap_handler+0x1b0/0x1b0
[56195.358595] [<ffffffff816cd5dc>] ret_from_fork+0x7c/0xb0
[56195.364105] [<ffffffff81065990>] ? proc_cap_handler+0x1b0/0x1b0



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