commit: 05eb0f252b04aa94ace0794f73d56c6a02351d80
From: Kay Sievers <kay.siev...@vrfy.org>
Date: Sun, 31 Jul 2011 22:21:35 +0200
Subject: [PATCH] loop: fix deadlock when sysfs and LOOP_CLR_FD race against
each other
LOOP_CLR_FD takes lo->lo_ctl_mutex and tries to remove the loop sysfs
files. Sysfs calls show() and waits for lo->lo_ctl_mutex. LOOP_CLR_FD
waits for show() to finish to remove the sysfs file.
cat /sys/class/block/loop0/loop/backing_file
mutex_lock_nested+0x176/0x350
? loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
? loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
dev_attr_show+0x1b/0x60
? sysfs_read_file+0x86/0x1a0
? __get_free_pages+0x12/0x50
sysfs_read_file+0xaf/0x1a0
ioctl(LOOP_CLR_FD):
wait_for_common+0x12c/0x180
? try_to_wake_up+0x2a0/0x2a0
wait_for_completion+0x18/0x20
sysfs_deactivate+0x178/0x180
? sysfs_addrm_finish+0x43/0x70
? sysfs_addrm_start+0x1d/0x20
sysfs_addrm_finish+0x43/0x70
sysfs_hash_and_remove+0x85/0xa0
sysfs_remove_group+0x59/0x100
loop_clr_fd+0x1dc/0x3f0 [loop]
lo_ioctl+0x223/0x7a0 [loop]
Instead of taking the lo_ctl_mutex from sysfs code, take the inner
lo->lo_lock, to protect the access to the backing_file data.
Thanks to Tejun for help debugging and finding a solution.
Cc: Milan Broz <mb...@redhat.com>
Cc: Tejun Heo <t...@kernel.org>
Signed-off-by: Kay Sievers <kay.siev...@vrfy.org>
Cc: sta...@kernel.org
Signed-off-by: Jens Axboe <jax...@fusionio.com>
---
drivers/block/loop.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 3defc52..4720c7a 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -743,10 +743,10 @@ static ssize_t loop_attr_backing_file_show(struct
loop_device *lo, char *buf)
ssize_t ret;
char *p = NULL;
- mutex_lock(&lo->lo_ctl_mutex);
+ spin_lock_irq(&lo->lo_lock);
if (lo->lo_backing_file)
p = d_path(&lo->lo_backing_file->f_path, buf, PAGE_SIZE - 1);
- mutex_unlock(&lo->lo_ctl_mutex);
+ spin_unlock_irq(&lo->lo_lock);
if (IS_ERR_OR_NULL(p))
ret = PTR_ERR(p);
@@ -1000,7 +1000,9 @@ static int loop_clr_fd(struct loop_device *lo, struct
block_device *bdev)
kthread_stop(lo->lo_thread);
+ spin_lock_irq(&lo->lo_lock);
lo->lo_backing_file = NULL;
+ spin_unlock_irq(&lo->lo_lock);
loop_release_xfer(lo);
lo->transfer = NULL;
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