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Subject[PATCH v1 3/7] block: loop: fix another reread part failure
Date
loop_clr_fd() can be run piggyback with lo_release(), and
under this situation, reread partition may always fail because
bd_mutex has been held already.

This patch detects the situation by the reference count, and
call __blkdev_reread_part() to avoid acquiring the lock again.

In the meantime, this patch switches to new kernel APIs
of blkdev_reread_part() and __blkdev_reread_part().

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
drivers/block/loop.c | 30 ++++++++++++++++++++++++++----
1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 0d9f014..9f17054 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -530,6 +530,28 @@ static int loop_flush(struct loop_device *lo)
return loop_switch(lo, NULL);
}

+static void loop_reread_partitions(struct loop_device *lo,
+ struct block_device *bdev)
+{
+ 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);
+ if (rc)
+ pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
+ __func__, lo->lo_number, lo->lo_file_name, rc);
+}
+
/*
* loop_change_fd switched the backing store of a loopback device to
* a new file. This is useful for operating system installers to free up
@@ -578,7 +600,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,

fput(old_file);
if (lo->lo_flags & LO_FLAGS_PARTSCAN)
- ioctl_by_bdev(bdev, BLKRRPART, 0);
+ loop_reread_partitions(lo, bdev);
return 0;

out_putf:
@@ -809,7 +831,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
if (part_shift)
lo->lo_flags |= LO_FLAGS_PARTSCAN;
if (lo->lo_flags & LO_FLAGS_PARTSCAN)
- ioctl_by_bdev(bdev, BLKRRPART, 0);
+ loop_reread_partitions(lo, bdev);

/* Grab the block_device to prevent its destruction after we
* put /dev/loopXX inode. Later in loop_clr_fd() we bdput(bdev).
@@ -927,7 +949,7 @@ static int loop_clr_fd(struct loop_device *lo)
blk_mq_unfreeze_queue(lo->lo_queue);

if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
- ioctl_by_bdev(bdev, BLKRRPART, 0);
+ loop_reread_partitions(lo, bdev);
lo->lo_flags = 0;
if (!part_shift)
lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
@@ -1002,7 +1024,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
!(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
lo->lo_flags |= LO_FLAGS_PARTSCAN;
lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
- ioctl_by_bdev(lo->lo_device, BLKRRPART, 0);
+ loop_reread_partitions(lo, lo->lo_device);
}

lo->lo_encrypt_key_size = info->lo_encrypt_key_size;
--
1.7.9.5


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