]> git.proxmox.com Git - mirror_ubuntu-kernels.git/commit
mm: dmapool: add/remove sysfs file outside of the pool lock lock
authorSebastian Andrzej Siewior <bigeasy@linutronix.de>
Thu, 9 Oct 2014 22:28:50 +0000 (15:28 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 10 Oct 2014 02:25:59 +0000 (22:25 -0400)
commit01c2965f0723a25209d5cf4cac630ed0f6d0edf4
tree4d3641ba5e946f22d22a0c06093318fa6086b701
parent6f817f4cda68b09621312ec5ba84217bc5e37b3d
mm: dmapool: add/remove sysfs file outside of the pool lock lock

cat /sys/.../pools followed by removal the device leads to:

|======================================================
|[ INFO: possible circular locking dependency detected ]
|3.17.0-rc4+ #1498 Not tainted
|-------------------------------------------------------
|rmmod/2505 is trying to acquire lock:
| (s_active#28){++++.+}, at: [<c017f754>] kernfs_remove_by_name_ns+0x3c/0x88
|
|but task is already holding lock:
| (pools_lock){+.+.+.}, at: [<c011494c>] dma_pool_destroy+0x18/0x17c
|
|which lock already depends on the new lock.
|the existing dependency chain (in reverse order) is:
|
|-> #1 (pools_lock){+.+.+.}:
|   [<c0114ae8>] show_pools+0x30/0xf8
|   [<c0313210>] dev_attr_show+0x1c/0x48
|   [<c0180e84>] sysfs_kf_seq_show+0x88/0x10c
|   [<c017f960>] kernfs_seq_show+0x24/0x28
|   [<c013efc4>] seq_read+0x1b8/0x480
|   [<c011e820>] vfs_read+0x8c/0x148
|   [<c011ea10>] SyS_read+0x40/0x8c
|   [<c000e960>] ret_fast_syscall+0x0/0x48
|
|-> #0 (s_active#28){++++.+}:
|   [<c017e9ac>] __kernfs_remove+0x258/0x2ec
|   [<c017f754>] kernfs_remove_by_name_ns+0x3c/0x88
|   [<c0114a7c>] dma_pool_destroy+0x148/0x17c
|   [<c03ad288>] hcd_buffer_destroy+0x20/0x34
|   [<c03a4780>] usb_remove_hcd+0x110/0x1a4

The problem is the lock order of pools_lock and kernfs_mutex in
dma_pool_destroy() vs show_pools() call path.

This patch breaks out the creation of the sysfs file outside of the
pools_lock mutex.  The newly added pools_reg_lock ensures that there is no
race of create vs destroy code path in terms whether or not the sysfs file
has to be deleted (and was it deleted before we try to create a new one)
and what to do if device_create_file() failed.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/dmapool.c