| From: Ming Lei <tom.leiming@gmail.com> |
| Date: Mon, 13 Feb 2012 22:53:20 +0800 |
| Subject: Fix circular locking dependency (3.3-rc2) |
| MIME-Version: 1.0 |
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| |
| commit 864533ceb6db336dead389577c102a8b792a121a upstream. |
| |
| 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> |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| drivers/gpio/gpiolib.c | 8 +++++--- |
| 1 file changed, 5 insertions(+), 3 deletions(-) |
| |
| --- a/drivers/gpio/gpiolib.c |
| +++ b/drivers/gpio/gpiolib.c |
| @@ -877,6 +877,7 @@ void gpio_unexport(unsigned gpio) |
| { |
| struct gpio_desc *desc; |
| int status = 0; |
| + struct device *dev = NULL; |
| |
| if (!gpio_is_valid(gpio)) { |
| status = -EINVAL; |
| @@ -888,19 +889,20 @@ 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); |
