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Subjectc/r: broken locking when executing map_files
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Hi all,

I've stumbled on several lockdep warnings when playing with the new files created under /proc/[pid], specifically 'map_files'.

My theory is that files under map_files shouldn't be executable, but since I'm not sure what the usermode code for c/r does exactly, I should probably confirm that first. If it's indeed the case, you can probably skip the rest of this mail.

First, if I try to simply execute one of the mappings:

sh-4.2# ls -al
total 0
dr-x------ 2 root 0 0 May 2 16:51 .
dr-xr-xr-x 9 root 0 0 May 2 16:51 ..
lr-------- 1 root 0 64 May 2 16:51 400000-4b3000 -> /host/bin/bash
[...]

sh-4.2# ./400000-4b3000

I get the following splat:

[ 141.769863]
[ 141.770019] =============================================
[ 141.770019] [ INFO: possible recursive locking detected ]
[ 141.770019] 3.4.0-rc5-next-20120501-sasha #104 Tainted: G W
[ 141.770019] ---------------------------------------------
[ 141.770019] sh/4464 is trying to acquire lock:
[ 141.770019] (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff810b518f>] mm_access+0x2f/0xb0
[ 141.770019]
[ 141.770019] but task is already holding lock:
[ 141.770019] (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff811f1742>] prepare_bprm_creds+0x32/0x80
[ 141.770019]
[ 141.770019] other info that might help us debug this:
[ 141.770019] Possible unsafe locking scenario:
[ 141.770019]
[ 141.770019] CPU0
[ 141.770019] ----
[ 141.770019] lock(&sig->cred_guard_mutex);
[ 141.770019] lock(&sig->cred_guard_mutex);
[ 141.770019]
[ 141.770019] *** DEADLOCK ***
[ 141.770019]
[ 141.770019] May be due to missing lock nesting notation
[ 141.770019]
[ 141.770019] 1 lock held by sh/4464:
[ 141.770019] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff811f1742>] prepare_bprm_creds+0x32/0x80
[ 141.770019]
[ 141.770019] stack backtrace:
[ 141.770019] Pid: 4464, comm: sh Tainted: G W 3.4.0-rc5-next-20120501-sasha #104
[ 141.770019] Call Trace:
[ 141.770019] [<ffffffff8111b1e9>] print_deadlock_bug+0x119/0x140
[ 141.770019] [<ffffffff8111d3de>] validate_chain+0x5ee/0x790
[ 141.770019] [<ffffffff810f1938>] ? sched_clock_cpu+0x108/0x120
[ 141.770019] [<ffffffff8111d9a3>] __lock_acquire+0x423/0x4c0
[ 141.770019] [<ffffffff8107d4c6>] ? kvm_clock_read+0x46/0x80
[ 141.770019] [<ffffffff8111db1c>] lock_acquire+0xdc/0x120
[ 141.770019] [<ffffffff810b518f>] ? mm_access+0x2f/0xb0
[ 141.770019] [<ffffffff82d8f5d0>] __mutex_lock_common+0x60/0x590
[ 141.770019] [<ffffffff810b518f>] ? mm_access+0x2f/0xb0
[ 141.770019] [<ffffffff810e808e>] ? sub_preempt_count+0xae/0xf0
[ 141.770019] [<ffffffff810b518f>] ? mm_access+0x2f/0xb0
[ 141.770019] [<ffffffff82d8fb90>] mutex_lock_killable_nested+0x40/0x50
[ 141.770019] [<ffffffff810b518f>] mm_access+0x2f/0xb0
[ 141.770019] [<ffffffff810d6f80>] ? alloc_pid+0x210/0x210
[ 141.770019] [<ffffffff81255124>] map_files_d_revalidate+0x74/0x250
[ 141.770019] [<ffffffff811f9175>] do_lookup+0x1d5/0x300
[ 141.770019] [<ffffffff811f95e0>] do_last+0x180/0x850
[ 141.770019] [<ffffffff811faa57>] path_openat+0xd7/0x4a0
[ 141.770019] [<ffffffff810562ad>] ? sched_clock+0x1d/0x30
[ 141.770019] [<ffffffff810f17c5>] ? sched_clock_local+0x25/0x90
[ 141.770019] [<ffffffff810f1938>] ? sched_clock_cpu+0x108/0x120
[ 141.770019] [<ffffffff811faf34>] do_filp_open+0x44/0xa0
[ 141.770019] [<ffffffff810e7951>] ? get_parent_ip+0x11/0x50
[ 141.770019] [<ffffffff810e808e>] ? sub_preempt_count+0xae/0xf0
[ 141.770019] [<ffffffff82d92bb0>] ? _raw_spin_unlock+0x30/0x60
[ 141.770019] [<ffffffff811f2fad>] open_exec+0x2d/0xf0
[ 141.770019] [<ffffffff811f403e>] do_execve_common+0xfe/0x320
[ 141.770019] [<ffffffff811f42e5>] do_execve+0x35/0x40
[ 141.770019] [<ffffffff81057a41>] sys_execve+0x51/0x80
[ 141.770019] [<ffffffff82d9407c>] stub_execve+0x6c/0xc0

And another (different) variant of this, is if you try listing directories combined with execves:

[ 183.908022] ======================================================
[ 183.908022] [ INFO: possible circular locking dependency detected ]
[ 183.908022] 3.4.0-rc5-next-20120501-sasha #104 Tainted: G W
[ 183.908022] -------------------------------------------------------
[ 183.908022] trinity/21028 is trying to acquire lock:
[ 183.908022] (&sb->s_type->i_mutex_key#10){+.+.+.}, at: [<ffffffff811f921d>] do_lookup+0x27d/0x300
[ 183.908022]
[ 183.908022] but task is already holding lock:
[ 183.908022] (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff811f1742>] prepare_bprm_creds+0x32/0x80
[ 183.908022]
[ 183.908022] which lock already depends on the new lock.
[ 183.908022]
[ 183.908022]
[ 183.908022] the existing dependency chain (in reverse order) is:
[ 183.908022]
[ 183.908022] -> #1 (&sig->cred_guard_mutex){+.+.+.}:
[ 183.908022] [<ffffffff8111d48e>] validate_chain+0x69e/0x790
[ 183.908022] [<ffffffff8111d9a3>] __lock_acquire+0x423/0x4c0
[ 183.908022] [<ffffffff8111db1c>] lock_acquire+0xdc/0x120
[ 183.908022] [<ffffffff82d8f5d0>] __mutex_lock_common+0x60/0x590
[ 183.908022] [<ffffffff82d8fb90>] mutex_lock_killable_nested+0x40/0x50
[ 183.908022] [<ffffffff81252a1f>] task_access_lock+0x2f/0x70
[ 183.908022] [<ffffffff81253592>] proc_map_files_readdir+0x82/0x470
[ 183.943078] [<ffffffff811ff53c>] vfs_readdir+0x7c/0xd0
[ 183.943078] [<ffffffff811ff712>] sys_getdents+0x92/0xf0
[ 183.943078] [<ffffffff82d93bb9>] system_call_fastpath+0x16/0x1b
[ 183.943078]
[ 183.943078] -> #0 (&sb->s_type->i_mutex_key#10){+.+.+.}:
[ 183.943078] [<ffffffff8111ca3f>] check_prev_add+0x11f/0x4d0
[ 183.943078] [<ffffffff8111d48e>] validate_chain+0x69e/0x790
[ 183.943078] [<ffffffff8111d9a3>] __lock_acquire+0x423/0x4c0
[ 183.943078] [<ffffffff8111db1c>] lock_acquire+0xdc/0x120
[ 183.943078] [<ffffffff82d8f5d0>] __mutex_lock_common+0x60/0x590
[ 183.943078] [<ffffffff82d8fc30>] mutex_lock_nested+0x40/0x50
[ 183.943078] [<ffffffff811f921d>] do_lookup+0x27d/0x300
[ 183.943078] [<ffffffff811f95e0>] do_last+0x180/0x850
[ 183.943078] [<ffffffff811faa57>] path_openat+0xd7/0x4a0
[ 183.943078] [<ffffffff811faf34>] do_filp_open+0x44/0xa0
[ 183.943078] [<ffffffff811f2fad>] open_exec+0x2d/0xf0
[ 183.943078] [<ffffffff811f403e>] do_execve_common+0xfe/0x320
[ 183.943078] [<ffffffff811f42e5>] do_execve+0x35/0x40
[ 183.943078] [<ffffffff81057a41>] sys_execve+0x51/0x80
[ 183.943078] [<ffffffff82d9407c>] stub_execve+0x6c/0xc0
[ 183.943078]
[ 183.943078] other info that might help us debug this:
[ 183.943078]
[ 183.943078] Possible unsafe locking scenario:
[ 183.943078]
[ 183.943078] CPU0 CPU1
[ 183.943078] ---- ----
[ 183.943078] lock(&sig->cred_guard_mutex);
[ 183.943078] lock(&sb->s_type->i_mutex_key#10);
[ 183.943078] lock(&sig->cred_guard_mutex);
[ 183.943078] lock(&sb->s_type->i_mutex_key#10);
[ 183.943078]
[ 183.943078] *** DEADLOCK ***
[ 183.943078]
[ 183.943078] 1 lock held by trinity/21028:
[ 183.943078] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff811f1742>] prepare_bprm_creds+0x32/0x80
[ 183.943078]
[ 183.943078] stack backtrace:
[ 183.943078] Pid: 21028, comm: trinity Tainted: G W 3.4.0-rc5-next-20120501-sasha #104
[ 183.943078] Call Trace:
[ 183.943078] [<ffffffff8111b543>] print_circular_bug+0x103/0x120
[ 183.943078] [<ffffffff8111ca3f>] check_prev_add+0x11f/0x4d0
[ 183.943078] [<ffffffff8111d48e>] validate_chain+0x69e/0x790
[ 183.943078] [<ffffffff810f1938>] ? sched_clock_cpu+0x108/0x120
[ 183.943078] [<ffffffff8111d9a3>] __lock_acquire+0x423/0x4c0
[ 183.943078] [<ffffffff8111db1c>] lock_acquire+0xdc/0x120
[ 183.943078] [<ffffffff811f921d>] ? do_lookup+0x27d/0x300
[ 183.943078] [<ffffffff82d8f5d0>] __mutex_lock_common+0x60/0x590
[ 183.943078] [<ffffffff811f921d>] ? do_lookup+0x27d/0x300
[ 183.943078] [<ffffffff810e7951>] ? get_parent_ip+0x11/0x50
[ 183.943078] [<ffffffff810e808e>] ? sub_preempt_count+0xae/0xf0
[ 183.943078] [<ffffffff811f921d>] ? do_lookup+0x27d/0x300
[ 183.943078] [<ffffffff82d8fc30>] mutex_lock_nested+0x40/0x50
[ 183.943078] [<ffffffff811f921d>] do_lookup+0x27d/0x300
[ 183.943078] [<ffffffff811f774b>] ? inode_permission+0xfb/0x110
[ 183.943078] [<ffffffff811f95e0>] do_last+0x180/0x850
[ 183.943078] [<ffffffff811faa57>] path_openat+0xd7/0x4a0
[ 183.943078] [<ffffffff810562ad>] ? sched_clock+0x1d/0x30
[ 183.943078] [<ffffffff810f17c5>] ? sched_clock_local+0x25/0x90
[ 183.943078] [<ffffffff810f1938>] ? sched_clock_cpu+0x108/0x120
[ 183.943078] [<ffffffff811faf34>] do_filp_open+0x44/0xa0
[ 183.943078] [<ffffffff810e7951>] ? get_parent_ip+0x11/0x50
[ 183.943078] [<ffffffff810e808e>] ? sub_preempt_count+0xae/0xf0
[ 183.943078] [<ffffffff82d92bb0>] ? _raw_spin_unlock+0x30/0x60
[ 183.943078] [<ffffffff811f2fad>] open_exec+0x2d/0xf0
[ 183.943078] [<ffffffff811f403e>] do_execve_common+0xfe/0x320
[ 183.943078] [<ffffffff818914fb>] ? strncpy_from_user+0x8b/0x180
[ 183.943078] [<ffffffff811f42e5>] do_execve+0x35/0x40
[ 183.943078] [<ffffffff81057a41>] sys_execve+0x51/0x80
[ 183.943078] [<ffffffff82d9407c>] stub_execve+0x6c/0xc0



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