On Thu, Dec 30, 2021 at 07:52:34PM +0900, Tetsuo Handa wrote:
OK. Two patches shown below. Are these look reasonable?
From 1409a49181efcc474fbae2cf4e60cbc37adf34aa Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Thu, 30 Dec 2021 18:41:05 +0900
Subject: [PATCH 1/2] loop: Revert "loop: make autoclear operation asynchronous"
Thanks, the revert fixes failures we saw recently in LTP tests,
which do mount/umount in close succession:
# for i in `seq 1 2`;do mount -t iso9660 -o loop /root/isofs.iso /mnt/isofs; umount /mnt/isofs/; done
mount: /mnt/isofs: WARNING: source write-protected, mounted read-only.
mount: /mnt/isofs: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.
umount: /mnt/isofs/: not mounted.
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.
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
drivers/block/loop.c | 65 ++++++++++++++++++++------------------------
drivers/block/loop.h | 1 -
2 files changed, 29 insertions(+), 37 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index b1b05c45c07c..e52a8a5e8cbc 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -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;
@@ -1144,6 +1144,8 @@ 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);
+ /* This is safe: open() is still holding a reference. */
+ module_put(THIS_MODULE);
blk_mq_unfreeze_queue(lo->lo_queue);
disk_force_media_change(lo->lo_disk, DISK_EVENT_MEDIA_CHANGE);
@@ -1151,52 +1153,44 @@ static void __loop_clr_fd(struct loop_device *lo)
if (lo->lo_flags & LO_FLAGS_PARTSCAN) {
int err;
- mutex_lock(&lo->lo_disk->open_mutex);
+ /*
+ * open_mutex has been held already in release path, so don't
+ * acquire it if this function is called in such case.
+ *
+ * If the reread partition isn't from release path, lo_refcnt
+ * must be at least one and it can only become zero when the
+ * current holder is released.
+ */
+ 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);
/* Device is gone, no point in returning error */
}
+ /*
+ * lo->lo_state is set to Lo_unbound here after above partscan has
+ * finished. There cannot be anybody else entering __loop_clr_fd() as
+ * Lo_rundown state protects us from all the other places trying to
+ * change the 'lo' device.
+ */
lo->lo_flags = 0;
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 +1222,7 @@ 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;
}
@@ -1754,7 +1747,7 @@ 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, true);
return;
} else if (lo->lo_state == Lo_bound) {
/*
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 {
--
2.32.0
