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Subjectvfs: INFO: possible circular locking dependency detected
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Date
Hi all,

I've started seeing the following warning while fuzzing inside a KVM guest with the latest -next:

[ 91.892449] ======================================================
[ 91.894167] [ INFO: possible circular locking dependency detected ]
[ 91.894167] 3.4.0-rc6-next-20120508-sasha-00003-g9f34dd7-dirty #120 Tainted: G W
[ 91.894167] -------------------------------------------------------
[ 91.894167] trinity/21513 is trying to acquire lock:
[ 91.894167] (&p->lock){+.+.+.}, at: [<ffffffff811fe53a>] seq_read+0x3a/0x420
[ 91.894167]
[ 91.894167] but task is already holding lock:
[ 91.894167] (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff811e2cb2>] prepare_bprm_creds+0x32/0x80
[ 91.894167]
[ 91.894167] which lock already depends on the new lock.
[ 91.894167]
[ 91.894167]
[ 91.894167] the existing dependency chain (in reverse order) is:
[ 91.894167]
[ 91.894167] -> #1 (&sig->cred_guard_mutex){+.+.+.}:
[ 91.894167] [<ffffffff81115e3e>] validate_chain.clone.26+0x70e/0x8c0
[ 91.894167] [<ffffffff8111910d>] __lock_acquire+0xa3d/0xb00
[ 91.894167] [<ffffffff81119881>] lock_acquire+0xd1/0x110
[ 91.894167] [<ffffffff82d89515>] __mutex_lock_common+0x65/0x570
[ 91.894167] [<ffffffff82d89b00>] mutex_lock_killable_nested+0x40/0x50
[ 91.894167] [<ffffffff810b1a7f>] mm_access+0x2f/0xb0
[ 91.894167] [<ffffffff8123f0c4>] m_start+0x74/0x1c0
[ 91.894167] [<ffffffff811fe687>] seq_read+0x187/0x420
[ 91.894167] [<ffffffff811dac8d>] vfs_read+0xbd/0x190
[ 91.894167] [<ffffffff811db04f>] sys_read+0x4f/0x90
[ 91.894167] [<ffffffff82d8dbbd>] system_call_fastpath+0x1a/0x1f
[ 91.894167]
[ 91.894167] -> #0 (&p->lock){+.+.+.}:
[ 91.894167] [<ffffffff8111523e>] check_prev_add+0x11e/0x610
[ 91.894167] [<ffffffff81115e3e>] validate_chain.clone.26+0x70e/0x8c0
[ 91.894167] [<ffffffff8111910d>] __lock_acquire+0xa3d/0xb00
[ 91.894167] [<ffffffff81119881>] lock_acquire+0xd1/0x110
[ 91.894167] [<ffffffff82d89515>] __mutex_lock_common+0x65/0x570
[ 91.894167] [<ffffffff82d89a60>] mutex_lock_nested+0x40/0x50
[ 91.894167] [<ffffffff811fe53a>] seq_read+0x3a/0x420
[ 91.894167] [<ffffffff81241769>] proc_reg_read+0xa9/0xe0
[ 91.894167] [<ffffffff811dac8d>] vfs_read+0xbd/0x190
[ 91.894167] [<ffffffff811e2a51>] kernel_read+0x41/0x60
[ 91.894167] [<ffffffff811e2ed3>] prepare_binprm+0x123/0x140
[ 91.894167] [<ffffffff811e3487>] do_execve_common.clone.32+0x197/0x320
[ 91.894167] [<ffffffff811e3626>] do_execve+0x16/0x20
[ 91.894167] [<ffffffff81056571>] sys_execve+0x51/0x80
[ 91.894167] [<ffffffff82d8e08c>] stub_execve+0x6c/0xc0
[ 91.894167]
[ 91.894167] other info that might help us debug this:
[ 91.894167]
[ 91.894167] Possible unsafe locking scenario:
[ 91.894167]
[ 91.894167] CPU0 CPU1
[ 91.894167] ---- ----
[ 91.894167] lock(&sig->cred_guard_mutex);
[ 91.894167] lock(&p->lock);
[ 91.894167] lock(&sig->cred_guard_mutex);
[ 91.894167] lock(&p->lock);
[ 91.894167]
[ 91.894167] *** DEADLOCK ***
[ 91.894167]
[ 91.894167] 1 lock held by trinity/21513:
[ 91.894167] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff811e2cb2>] prepare_bprm_creds+0x32/0x80
[ 91.894167]
[ 91.894167] stack backtrace:
[ 91.894167] Pid: 21513, comm: trinity Tainted: G W 3.4.0-rc6-next-20120508-sasha-00003-g9f34dd7-dirty #120
[ 91.894167] Call Trace:
[ 91.894167] [<ffffffff811144d7>] print_circular_bug+0x107/0x130
[ 91.894167] [<ffffffff8111523e>] check_prev_add+0x11e/0x610
[ 91.894167] [<ffffffff81115e3e>] validate_chain.clone.26+0x70e/0x8c0
[ 91.894167] [<ffffffff8111910d>] __lock_acquire+0xa3d/0xb00
[ 91.894167] [<ffffffff81116c06>] ? mark_held_locks+0xe6/0x120
[ 91.894167] [<ffffffff81119881>] lock_acquire+0xd1/0x110
[ 91.894167] [<ffffffff811fe53a>] ? seq_read+0x3a/0x420
[ 91.894167] [<ffffffff82d8d426>] ? retint_kernel+0x26/0x30
[ 91.894167] [<ffffffff82d89515>] __mutex_lock_common+0x65/0x570
[ 91.894167] [<ffffffff811fe53a>] ? seq_read+0x3a/0x420
[ 91.894167] [<ffffffff810b4879>] ? vprintk+0x3f9/0x480
[ 91.894167] [<ffffffff811fe53a>] ? seq_read+0x3a/0x420
[ 91.894167] [<ffffffff811fe500>] ? seq_open+0xb0/0xb0
[ 91.894167] [<ffffffff82d89a60>] mutex_lock_nested+0x40/0x50
[ 91.894167] [<ffffffff811fe53a>] seq_read+0x3a/0x420
[ 91.894167] [<ffffffff810e891e>] ? sub_preempt_count+0xae/0xe0
[ 91.894167] [<ffffffff811fe500>] ? seq_open+0xb0/0xb0
[ 91.894167] [<ffffffff81241769>] proc_reg_read+0xa9/0xe0
[ 91.894167] [<ffffffff811dac8d>] vfs_read+0xbd/0x190
[ 91.894167] [<ffffffff811e2a51>] kernel_read+0x41/0x60
[ 91.894167] [<ffffffff811e2ed3>] prepare_binprm+0x123/0x140
[ 91.894167] [<ffffffff811e3487>] do_execve_common.clone.32+0x197/0x320
[ 91.894167] [<ffffffff811e3626>] do_execve+0x16/0x20
[ 91.894167] [<ffffffff81056571>] sys_execve+0x51/0x80
[ 91.894167] [<ffffffff82d8e08c>] stub_execve+0x6c/0xc0


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