I'm sometimes a little slow, but I still fail to understand why we need
all this. Your cut down patch that moves the destroy_workqueue call
and the work_struct fixed all the know lockdep issues, right?
And the only other problem we're thinking off is that blk_mq_freeze_queue
could have the same effect, except that lockdep doesn't track it and
we've not seen it in the wild.
As far as I can tell we do not need the freeze at all for given that
by the time release is called I/O is quiesced. So with a little prep
work we should not need any of that. See below (this is actually
three patches, with the last one being a very slight rebase of your
patch):
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 01cbbfc4e9e24..91b56761392e2 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1006,10 +1006,10 @@ 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;
@@ -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)
+static void __loop_clr_fd(struct loop_device *lo, bool release)
{
struct file *filp;
gfp_t gfp = lo->old_gfp_mask;
@@ -1112,10 +1112,14 @@ static void __loop_clr_fd(struct loop_device *lo)
if (test_bit(QUEUE_FLAG_WC, &lo->lo_queue->queue_flags))
blk_queue_write_cache(lo->lo_queue, false, false);
- /* freeze request queue during the transition */
- blk_mq_freeze_queue(lo->lo_queue);
+ /*
+ * Freeze the request queue when unbinding on a live file descriptor and
+ * thus an open device. When called from ->release we are guaranteed
+ * that there is no I/O in progress already.
+ */
+ if (!release)
+ 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) {
@@ -1144,16 +1148,19 @@ static void __loop_clr_fd(struct loop_device *lo)
/* 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);
- blk_mq_unfreeze_queue(lo->lo_queue);
+ if (!release)
+ blk_mq_unfreeze_queue(lo->lo_queue);
disk_force_media_change(lo->lo_disk, DISK_EVENT_MEDIA_CHANGE);
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);
@@ -1164,39 +1171,17 @@ 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)
@@ -1228,8 +1213,7 @@ static int loop_clr_fd(struct loop_device *lo)
lo->lo_state = Lo_rundown;
mutex_unlock(&lo->lo_mutex);
- __loop_clr_fd(lo);
- loop_rundown_completed(lo);
+ __loop_clr_fd(lo, false);
return 0;
}
@@ -1754,15 +1738,8 @@ 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, true);
return;
- } else if (lo->lo_state == Lo_bound) {
- /*
- * Otherwise keep thread (if running) and config,
- * but flush possible ongoing bios in thread.
- */
- blk_mq_freeze_queue(lo->lo_queue);
- blk_mq_unfreeze_queue(lo->lo_queue);
}
out_unlock:
@@ -2080,6 +2057,8 @@ 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 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 {
