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loop: make autoclear operation asynchronous

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syzbot is reporting circular locking problem at __loop_clr_fd() [1], for
commit 87579e9b7d ("loop: use worker per cgroup instead of kworker")
is calling destroy_workqueue() with disk->open_mutex held.

This circular dependency cannot be broken unless we call __loop_clr_fd()
without holding disk->open_mutex. Therefore, defer __loop_clr_fd() from
lo_release() to a WQ context.

Link: https://syzkaller.appspot.com/bug?extid=643e4ce4b6ad1347d372 [1]
Reported-by: syzbot <syzbot+643e4ce4b6ad1347d372@syzkaller.appspotmail.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Tested-by: syzbot+643e4ce4b6ad1347d372@syzkaller.appspotmail.com
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/1ed7df28-ebd6-71fb-70e5-1c2972e05ddb@i-love.sakura.ne.jp
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tetsuo Handa 2021-12-13 21:55:27 +09:00 committed by Jens Axboe
parent c5eafd790e
commit 322c4293ec
2 changed files with 37 additions and 29 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

65
drivers/block/loop.c
View file

@ -1082,7 +1082,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
return error;
}
static void __loop_clr_fd(struct loop_device *lo, bool release)
static void __loop_clr_fd(struct loop_device *lo)
{
struct file *filp;
gfp_t gfp = lo->old_gfp_mask;
@ -1144,8 +1144,6 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
/* let user-space know about this change */
kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
mapping_set_gfp_mask(filp->f_mapping, gfp);
/* This is safe: open() is still holding a reference. */
module_put(THIS_MODULE);
blk_mq_unfreeze_queue(lo->lo_queue);
disk_force_media_change(lo->lo_disk, DISK_EVENT_MEDIA_CHANGE);
@ -1153,44 +1151,52 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
if (lo->lo_flags & LO_FLAGS_PARTSCAN) {
int err;
/*
* open_mutex has been held already in release path, so don't
* acquire it if this function is called in such case.
*
* If the reread partition isn't from release path, lo_refcnt
* must be at least one and it can only become zero when the
* current holder is released.
*/
if (!release)
mutex_lock(&lo->lo_disk->open_mutex);
mutex_lock(&lo->lo_disk->open_mutex);
err = bdev_disk_changed(lo->lo_disk, false);
if (!release)
mutex_unlock(&lo->lo_disk->open_mutex);
mutex_unlock(&lo->lo_disk->open_mutex);
if (err)
pr_warn("%s: partition scan of loop%d failed (rc=%d)\n",
__func__, lo->lo_number, err);
/* Device is gone, no point in returning error */
}
/*
* lo->lo_state is set to Lo_unbound here after above partscan has
* finished. There cannot be anybody else entering __loop_clr_fd() as
* Lo_rundown state protects us from all the other places trying to
* change the 'lo' device.
*/
lo->lo_flags = 0;
if (!part_shift)
lo->lo_disk->flags |= GENHD_FL_NO_PART;
fput(filp);
}
static void loop_rundown_completed(struct loop_device *lo)
{
mutex_lock(&lo->lo_mutex);
lo->lo_state = Lo_unbound;
mutex_unlock(&lo->lo_mutex);
module_put(THIS_MODULE);
}
/*
* Need not hold lo_mutex to fput backing file. Calling fput holding
* lo_mutex triggers a circular lock dependency possibility warning as
* fput can take open_mutex which is usually taken before lo_mutex.
*/
fput(filp);
static void loop_rundown_workfn(struct work_struct *work)
{
struct loop_device *lo = container_of(work, struct loop_device,
rundown_work);
struct block_device *bdev = lo->lo_device;
struct gendisk *disk = lo->lo_disk;
__loop_clr_fd(lo);
kobject_put(&bdev->bd_device.kobj);
module_put(disk->fops->owner);
loop_rundown_completed(lo);
}
static void loop_schedule_rundown(struct loop_device *lo)
{
struct block_device *bdev = lo->lo_device;
struct gendisk *disk = lo->lo_disk;
__module_get(disk->fops->owner);
kobject_get(&bdev->bd_device.kobj);
INIT_WORK(&lo->rundown_work, loop_rundown_workfn);
queue_work(system_long_wq, &lo->rundown_work);
}
static int loop_clr_fd(struct loop_device *lo)
@ -1222,7 +1228,8 @@ static int loop_clr_fd(struct loop_device *lo)
lo->lo_state = Lo_rundown;
mutex_unlock(&lo->lo_mutex);
__loop_clr_fd(lo, false);
__loop_clr_fd(lo);
loop_rundown_completed(lo);
return 0;
}
@ -1747,7 +1754,7 @@ static void lo_release(struct gendisk *disk, fmode_t mode)
* In autoclear mode, stop the loop thread
* and remove configuration after last close.
*/
__loop_clr_fd(lo, true);
loop_schedule_rundown(lo);
return;
} else if (lo->lo_state == Lo_bound) {
/*

1
drivers/block/loop.h
View file

@ -56,6 +56,7 @@ struct loop_device {
struct gendisk *lo_disk;
struct mutex lo_mutex;
bool idr_visible;
struct work_struct rundown_work;
};
struct loop_cmd {