From: Tetsuo Handa Date: Sun, 26 Dec 2021 07:06:27 +0000 (+0900) Subject: make autoclear operation synchronous again X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=refs%2Fheads%2Fpart_tbl_mutex;p=users%2Fhch%2Fblock.git make autoclear operation synchronous again The kernel test robot is reporting that xfstest can fail at umount ext2 on xfs umount xfs sequence, for commit 322c4293ecc58110 ("loop: make autoclear operation asynchronous") broke what commit ("loop: Make explicit loop device destruction lazy") wanted to achieve. Although we cannot guarantee that nobody is holding a reference when "umount xfs" is called, we should try to close a race window opened by asynchronous autoclear operation. It turned out that there is no need to call flush_workqueue() from __loop_clr_fd(), for blk_mq_freeze_queue() blocks until all pending "struct work_struct" are processed by loop_process_work(). Revert commit 322c4293ecc58110 ("loop: make autoclear operation asynchronous"), and simply defer calling destroy_workqueue() till loop_remove(). Since a loop device is likely reused after once created thanks to ioctl(LOOP_CTL_GET_FREE), being unable to destroy corresponding WQ when ioctl(LOOP_CLR_FD) is called should be an acceptable waste. Reported-by: kernel test robot Suggested-by: Christoph Hellwig Tested-by: syzbot Signed-off-by: Tetsuo Handa Signed-off-by: Christoph Hellwig --- diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 998d08a18414..ff52b9b99f4f 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1004,10 +1004,10 @@ static int loop_configure(struct loop_device *lo, fmode_t mode, !file->f_op->write_iter) lo->lo_flags |= LO_FLAGS_READ_ONLY; - lo->workqueue = alloc_workqueue("loop%d", - WQ_UNBOUND | WQ_FREEZABLE, - 0, - lo->lo_number); + if (!lo->workqueue) + lo->workqueue = alloc_workqueue("loop%d", + WQ_UNBOUND | WQ_FREEZABLE, + 0, lo->lo_number); if (!lo->workqueue) { error = -ENOMEM; goto out_unlock; @@ -1113,7 +1113,6 @@ static void __loop_clr_fd(struct loop_device *lo) /* freeze request queue during the transition */ blk_mq_freeze_queue(lo->lo_queue); - destroy_workqueue(lo->workqueue); spin_lock_irq(&lo->lo_work_lock); list_for_each_entry_safe(worker, pos, &lo->idle_worker_list, idle_list) { @@ -1151,39 +1150,17 @@ static void __loop_clr_fd(struct loop_device *lo) 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); -} - -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); + /* + * 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 int loop_clr_fd(struct loop_device *lo) @@ -1216,7 +1193,6 @@ static int loop_clr_fd(struct loop_device *lo) mutex_unlock(&lo->lo_mutex); __loop_clr_fd(lo); - loop_rundown_completed(lo); return 0; } @@ -1741,7 +1717,7 @@ static void lo_release(struct gendisk *disk, fmode_t mode) * In autoclear mode, stop the loop thread * and remove configuration after last close. */ - loop_schedule_rundown(lo); + __loop_clr_fd(lo); return; } else if (lo->lo_state == Lo_bound) { /* @@ -2067,6 +2043,8 @@ static void loop_remove(struct loop_device *lo) mutex_unlock(&loop_ctl_mutex); /* There is no route which can find this loop device. */ mutex_destroy(&lo->lo_mutex); + if (lo->workqueue) + destroy_workqueue(lo->workqueue); kfree(lo); } diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 918a7a2dc025..082d4b6bfc6a 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -56,7 +56,6 @@ struct loop_device { struct gendisk *lo_disk; struct mutex lo_mutex; bool idr_visible; - struct work_struct rundown_work; }; struct loop_cmd {