Re: Possible circular locking dependency (3.3-rc2)

[Maciej Rutecki]

On Åroda, 8 lutego 2012 o 13:41:48 Felipe Balbi wrote:
> Hi guys,
> 
> I have just triggered the folllowing:
> 
> [   84.860321] ======================================================
> [   84.860321] [ INFO: possible circular locking dependency detected ]
> [   84.860321] 3.3.0-rc2-00026-ge4e8a39 #474 Not tainted
> [   84.860321] -------------------------------------------------------
> [   84.860321] bash/949 is trying to acquire lock:
> [   84.860321]  (sysfs_lock){+.+.+.}, at: [<c0275358>]
> gpio_value_store+0x24/0xcc [   84.860321]
> [   84.860321] but task is already holding lock:
> [   84.860321]  (s_active#22){++++.+}, at: [<c016996c>]
> sysfs_write_file+0xdc/0x184 [   84.911468]
> [   84.911468] which lock already depends on the new lock.
> [   84.911468]
> [   84.920043]
> [   84.920043] the existing dependency chain (in reverse order) is:
> [   84.920043]
> [   84.927886] -> #1 (s_active#22){++++.+}:
> [   84.927886]        [<c008f640>] check_prevs_add+0xdc/0x150
> [   84.927886]        [<c008fc18>] validate_chain.clone.24+0x564/0x694
> [   84.927886]        [<c0090cdc>] __lock_acquire+0x49c/0x980
> [   84.951660]        [<c0091838>] lock_acquire+0x98/0x100
> [   84.951660]        [<c016a8e8>] sysfs_deactivate+0xb0/0x100
> [   84.962982]        [<c016b1b4>] sysfs_addrm_finish+0x2c/0x6c
> [   84.962982]        [<c016b8bc>] sysfs_remove_dir+0x84/0x98
> [   84.962982]        [<c02590d8>] kobject_del+0x10/0x78
> [   84.974670]        [<c02c29e8>] device_del+0x140/0x170
> [   84.974670]        [<c02c2a24>] device_unregister+0xc/0x18
> [   84.985382]        [<c0276894>] gpio_unexport+0xbc/0xdc
> [   84.985382]        [<c02768c8>] gpio_free+0x14/0xfc
> [   85.001708]        [<c0276a28>] unexport_store+0x78/0x8c
> [   85.001708]        [<c02c5af8>] class_attr_store+0x18/0x24
> [   85.007293]        [<c0169990>] sysfs_write_file+0x100/0x184
> [   85.018981]        [<c0109d48>] vfs_write+0xb4/0x148
> [   85.018981]        [<c0109fd0>] sys_write+0x40/0x70
> [   85.018981]        [<c0013cc0>] ret_fast_syscall+0x0/0x3c
> [   85.035003]
> [   85.035003] -> #0 (sysfs_lock){+.+.+.}:
> [   85.035003]        [<c008f54c>] check_prev_add+0x680/0x698
> [   85.035003]        [<c008f640>] check_prevs_add+0xdc/0x150
> [   85.052093]        [<c008fc18>] validate_chain.clone.24+0x564/0x694
> [   85.052093]        [<c0090cdc>] __lock_acquire+0x49c/0x980
> [   85.052093]        [<c0091838>] lock_acquire+0x98/0x100
> [   85.069885]        [<c047e280>] mutex_lock_nested+0x3c/0x2f4
> [   85.069885]        [<c0275358>] gpio_value_store+0x24/0xcc
> [   85.069885]        [<c02c18dc>] dev_attr_store+0x18/0x24
> [   85.087158]        [<c0169990>] sysfs_write_file+0x100/0x184
> [   85.087158]        [<c0109d48>] vfs_write+0xb4/0x148
> [   85.098297]        [<c0109fd0>] sys_write+0x40/0x70
> [   85.098297]        [<c0013cc0>] ret_fast_syscall+0x0/0x3c
> [   85.109069]
> [   85.109069] other info that might help us debug this:
> [   85.109069]
> [   85.117462]  Possible unsafe locking scenario:
> [   85.117462]
> [   85.117462]        CPU0                    CPU1
> [   85.128417]        ----                    ----
> [   85.128417]   lock(s_active#22);
> [   85.128417]                                lock(sysfs_lock);
> [   85.128417]                                lock(s_active#22);
> [   85.142486]   lock(sysfs_lock);
> [   85.151794]
> [   85.151794]  *** DEADLOCK ***
> [   85.151794]
> [   85.151794] 2 locks held by bash/949:
> [   85.158020]  #0:  (&buffer->mutex){+.+.+.}, at: [<c01698b8>]
> sysfs_write_file+0x28/0x184 [   85.170349]  #1:  (s_active#22){++++.+},
> at: [<c016996c>] sysfs_write_file+0xdc/0x184 [   85.170349]
> [   85.178588] stack backtrace:
> [   85.178588] [<c001b824>] (unwind_backtrace+0x0/0xf0) from [<c008de64>]
> (print_circular_bug+0x100/0x114) [   85.193023] [<c008de64>]
> (print_circular_bug+0x100/0x114) from [<c008f54c>]
> (check_prev_add+0x680/0x698) [   85.193023] [<c008f54c>]
> (check_prev_add+0x680/0x698) from [<c008f640>]
> (check_prevs_add+0xdc/0x150) [   85.212524] [<c008f640>]
> (check_prevs_add+0xdc/0x150) from [<c008fc18>]
> (validate_chain.clone.24+0x564/0x694) [   85.212524] [<c008fc18>]
> (validate_chain.clone.24+0x564/0x694) from [<c0090cdc>]
> (__lock_acquire+0x49c/0x980) [   85.233306] [<c0090cdc>]
> (__lock_acquire+0x49c/0x980) from [<c0091838>] (lock_acquire+0x98/0x100) [
>   85.233306] [<c0091838>] (lock_acquire+0x98/0x100) from [<c047e280>]
> (mutex_lock_nested+0x3c/0x2f4) [   85.242614] [<c047e280>]
> (mutex_lock_nested+0x3c/0x2f4) from [<c0275358>]
> (gpio_value_store+0x24/0xcc) [   85.261840] [<c0275358>]
> (gpio_value_store+0x24/0xcc) from [<c02c18dc>] (dev_attr_store+0x18/0x24)
> [   85.261840] [<c02c18dc>] (dev_attr_store+0x18/0x24) from [<c0169990>]
> (sysfs_write_file+0x100/0x184) [   85.271240] [<c0169990>]
> (sysfs_write_file+0x100/0x184) from [<c0109d48>] (vfs_write+0xb4/0x148) [ 
>  85.290008] [<c0109d48>] (vfs_write+0xb4/0x148) from [<c0109fd0>]
> (sys_write+0x40/0x70) [   85.298400] [<c0109fd0>] (sys_write+0x40/0x70)
> from [<c0013cc0>] (ret_fast_syscall+0x0/0x3c) -bash: echo: write error:
> Operation not permitted
> 
> the way to trigger is:
> 
> 
> root@legolas:~# cd /sys/class/gpio/
> root@legolas:/sys/class/gpio# echo 2 > export
> root@legolas:/sys/class/gpio# echo 2 > unexport
> root@legolas:/sys/class/gpio# echo 2 > export
> root@legolas:/sys/class/gpio# cd gpio2/
> root@legolas:/sys/class/gpio/gpio2# echo 1 > value

I created a Bugzilla entry at 
https://bugzilla.kernel.org/show_bug.cgi?id=42761
for your bug/regression report, please add your address to the CC list in 
there, thanks!

-- 
Maciej Rutecki
http://www.mrutecki.pl
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