[PATCH 13/14] loop: Move loop_reread_partitions() out of loop_ctl_mutex
From: Jan Kara <jack@suse.cz>
Date: 2018-09-27 17:55:05
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
Calling loop_reread_partitions() under loop_ctl_mutex causes lockdep to complain about circular lock dependency between bdev->bd_mutex and lo->lo_ctl_mutex. The problem is that on loop device open or close lo_open() and lo_release() get called with bdev->bd_mutex held and they need to acquire loop_ctl_mutex. OTOH when loop_reread_partitions() is called with loop_ctl_mutex held, it will call blkdev_reread_part() which acquires bdev->bd_mutex. See syzbot report for details [1]. Move all calls of loop_rescan_partitions() out of loop_ctl_mutex to avoid lockdep warning and fix deadlock possibility. [1] https://syzkaller.appspot.com/bug?id=bf154052f0eea4bc7712499e4569505907d1588 Reported-by: syzbot <redacted> Signed-off-by: Jan Kara <jack@suse.cz> --- drivers/block/loop.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index cce1a32ae6d0..d2be85c48f03 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c@@ -680,6 +680,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, { struct file *file, *old_file; int error; + bool partscan; error = mutex_lock_killable_nested(&loop_ctl_mutex, 1); if (error)
@@ -721,9 +722,10 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, blk_mq_unfreeze_queue(lo->lo_queue); fput(old_file); - if (lo->lo_flags & LO_FLAGS_PARTSCAN) - loop_reread_partitions(lo, bdev); + partscan = lo->lo_flags & LO_FLAGS_PARTSCAN; mutex_unlock(&loop_ctl_mutex); + if (partscan) + loop_reread_partitions(lo, bdev); return 0; out_putf:
@@ -904,6 +906,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, int lo_flags = 0; int error; loff_t size; + bool partscan; /* This is safe, since we have a reference from open(). */ __module_get(THIS_MODULE);
@@ -970,14 +973,15 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, lo->lo_state = Lo_bound; if (part_shift) lo->lo_flags |= LO_FLAGS_PARTSCAN; - if (lo->lo_flags & LO_FLAGS_PARTSCAN) - loop_reread_partitions(lo, bdev); + partscan = lo->lo_flags & LO_FLAGS_PARTSCAN; /* Grab the block_device to prevent its destruction after we * put /dev/loopXX inode. Later in __loop_clr_fd() we bdput(bdev). */ bdgrab(bdev); mutex_unlock(&loop_ctl_mutex); + if (partscan) + loop_reread_partitions(lo, bdev); return 0; out_unlock:
@@ -1158,6 +1162,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) int err; struct loop_func_table *xfer; kuid_t uid = current_uid(); + struct block_device *bdev; + bool partscan = false; err = mutex_lock_killable_nested(&loop_ctl_mutex, 1); if (err)
@@ -1246,10 +1252,13 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) !(lo->lo_flags & LO_FLAGS_PARTSCAN)) { lo->lo_flags |= LO_FLAGS_PARTSCAN; lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN; - loop_reread_partitions(lo, lo->lo_device); + bdev = lo->lo_device; + partscan = true; } out_unlock: mutex_unlock(&loop_ctl_mutex); + if (partscan) + loop_reread_partitions(lo, bdev); return err; }
--
2.16.4