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authorMing Lei <tom.leiming@gmail.com>2012-02-13 22:53:20 +0800
committerGrant Likely <grant.likely@secretlab.ca>2012-02-15 13:06:07 -0700
commit864533ceb6db336dead389577c102a8b792a121a (patch)
treea9535b1d26af60737f136f0e9c717300f303f6f2 /drivers/gpio/gpiolib.c
parentff64abefb6680dfc2aca7ecaa5e695949e7335c9 (diff)
Fix circular locking dependency (3.3-rc2)
Hi, On Wed, Feb 8, 2012 at 8:41 PM, Felipe Balbi <balbi@ti.com> 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 Looks 'sysfs_lock' needn't to be held for unregister, so the patch below may fix the problem. Acked-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Diffstat (limited to 'drivers/gpio/gpiolib.c')
-rw-r--r--drivers/gpio/gpiolib.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 17fdf4b6af9..d77354068b9 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -873,6 +873,7 @@ void gpio_unexport(unsigned gpio)
{
struct gpio_desc *desc;
int status = 0;
+ struct device *dev = NULL;
if (!gpio_is_valid(gpio)) {
status = -EINVAL;
@@ -884,19 +885,20 @@ void gpio_unexport(unsigned gpio)
desc = &gpio_desc[gpio];
if (test_bit(FLAG_EXPORT, &desc->flags)) {
- struct device *dev = NULL;
dev = class_find_device(&gpio_class, NULL, desc, match_export);
if (dev) {
gpio_setup_irq(desc, dev, 0);
clear_bit(FLAG_EXPORT, &desc->flags);
- put_device(dev);
- device_unregister(dev);
} else
status = -ENODEV;
}
mutex_unlock(&sysfs_lock);
+ if (dev) {
+ device_unregister(dev);
+ put_device(dev);
+ }
done:
if (status)
pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);