From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
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() after ensuring that the worker rbtree and repaing
timer are kept alive while the loop device exists.
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 <oliver.sang@xxxxxxxxx>
Suggested-by: Christoph Hellwig <hch@xxxxxx>
Tested-by: syzbot <syzbot+643e4ce4b6ad1347d372@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
[hch: rebased, keep the work rbtree and timer around longer]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
drivers/block/loop.c | 71 ++++++++++++++------------------------------
drivers/block/loop.h | 1 -
2 files changed, 23 insertions(+), 49 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index fc0cdd1612b1d..cf7830a68113a 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1038,10 +1038,10 @@ 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;
@@ -1147,10 +1147,6 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
if (!release)
blk_mq_freeze_queue(lo->lo_queue);
- destroy_workqueue(lo->workqueue);
- loop_free_idle_workers(lo, true);
- del_timer_sync(&lo->timer);
-
spin_lock_irq(&lo->lo_lock);
filp = lo->lo_backing_file;
lo->lo_backing_file = NULL;
@@ -1176,9 +1172,11 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
if (lo->lo_flags & LO_FLAGS_PARTSCAN) {
int err;
- mutex_lock(&lo->lo_disk->open_mutex);
+ if (!release)
+ mutex_lock(&lo->lo_disk->open_mutex);
err = bdev_disk_changed(lo->lo_disk, false);
- mutex_unlock(&lo->lo_disk->open_mutex);
+ if (!release)
+ 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);
@@ -1189,39 +1187,17 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
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, true);
- 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)
@@ -1254,7 +1230,6 @@ static int loop_clr_fd(struct loop_device *lo)
mutex_unlock(&lo->lo_mutex);
__loop_clr_fd(lo, false);
- loop_rundown_completed(lo);
return 0;
}
@@ -1753,20 +1728,14 @@ static void lo_release(struct gendisk *disk, fmode_t mode)
return;
mutex_lock(&lo->lo_mutex);
- if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
- if (lo->lo_state != Lo_bound)
- goto out_unlock;
+ if (lo->lo_state == Lo_bound &&
+ (lo->lo_flags & LO_FLAGS_AUTOCLEAR)) {
lo->lo_state = Lo_rundown;
mutex_unlock(&lo->lo_mutex);
- /*
- * In autoclear mode, stop the loop thread
- * and remove configuration after last close.
- */
- loop_schedule_rundown(lo);
+ __loop_clr_fd(lo, true);
return;
}
-out_unlock:
mutex_unlock(&lo->lo_mutex);
}
@@ -2056,6 +2025,12 @@ static void loop_remove(struct loop_device *lo)
mutex_lock(&loop_ctl_mutex);
idr_remove(&loop_index_idr, lo->lo_number);
mutex_unlock(&loop_ctl_mutex);
+
+ if (lo->workqueue)
+ destroy_workqueue(lo->workqueue);
+ loop_free_idle_workers(lo, true);
+ del_timer_sync(&lo->timer);
+
/* There is no route which can find this loop device. */
mutex_destroy(&lo->lo_mutex);
kfree(lo);
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 918a7a2dc0259..082d4b6bfc6a6 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 {
--
2.30.2
