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Subject[PATCH 4.19 91/99] loop: Move special partition reread handling in loop_clr_fd()
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@suse.cz>

commit d57f3374ba4817f7c8d26fae8a13d20ac8d31b92 upstream.

The call of __blkdev_reread_part() from loop_reread_partition() happens
only when we need to invalidate partitions from loop_release(). Thus
move a detection for this into loop_clr_fd() and simplify
loop_reread_partition().

This makes loop_reread_partition() safe to use without loop_ctl_mutex
because we use only lo->lo_number and lo->lo_file_name in case of error
for reporting purposes (thus possibly reporting outdate information is
not a big deal) and we are safe from 'lo' going away under us by
elevated lo->lo_refcnt.

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 | 33 +++++++++++++++++++--------------
1 file changed, 19 insertions(+), 14 deletions(-)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -631,18 +631,7 @@ static void loop_reread_partitions(struc
{
int rc;

- /*
- * bd_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 (!atomic_read(&lo->lo_refcnt))
- rc = __blkdev_reread_part(bdev);
- else
- rc = blkdev_reread_part(bdev);
+ rc = blkdev_reread_part(bdev);
if (rc)
pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
__func__, lo->lo_number, lo->lo_file_name, rc);
@@ -1096,8 +1085,24 @@ static int __loop_clr_fd(struct loop_dev
module_put(THIS_MODULE);
blk_mq_unfreeze_queue(lo->lo_queue);

- if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
- loop_reread_partitions(lo, bdev);
+ if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev) {
+ /*
+ * bd_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 (!atomic_read(&lo->lo_refcnt))
+ err = __blkdev_reread_part(bdev);
+ else
+ err = blkdev_reread_part(bdev);
+ 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 */
+ err = 0;
+ }
lo->lo_flags = 0;
if (!part_shift)
lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;

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