4.20-stable review patch. If anyone has any objections, please let me know.
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From: Jan Kara jack@suse.cz
commit 85b0a54a82e4fbceeb1aebb7cb6909edd1a24668 upstream.
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 syzbot+4684a000d5abdade83fac55b1e7d1f935ef1936e@syzkaller.appspotmail.com Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/block/loop.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-)
--- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -679,6 +679,7 @@ static int loop_change_fd(struct loop_de { struct file *file, *old_file; int error; + bool partscan;
error = mutex_lock_killable_nested(&loop_ctl_mutex, 1); if (error) @@ -720,9 +721,10 @@ static int loop_change_fd(struct loop_de 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: @@ -903,6 +905,7 @@ static int loop_set_fd(struct loop_devic 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); @@ -969,14 +972,15 @@ static int loop_set_fd(struct loop_devic 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: @@ -1157,6 +1161,8 @@ loop_set_status(struct loop_device *lo, 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) @@ -1245,10 +1251,13 @@ out_unfreeze: !(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; }