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Subject[PATCH 3/6] 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
of bd_mutex which has been held in release path.

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

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

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
drivers/block/loop.c | 28 ++++++++++++++++++++++++----
1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 81a6bc1..80c9d87 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -528,6 +528,26 @@ 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;
+ bool in_release;
+
+ mutex_lock(&lo->lo_open_mutex);
+ in_release = lo->lo_refcnt == 0;
+ mutex_unlock(&lo->lo_open_mutex);
+
+ /* bd_mutex has been held already in release path */
+ if (in_release)
+ rc = blkdev_reread_part_nolock(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
@@ -576,7 +596,7 @@ 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:
@@ -807,7 +827,7 @@ 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).
@@ -933,7 +953,7 @@ static int loop_clr_fd(struct loop_device *lo)
mutex_unlock(&lo->lo_open_mutex);

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;
@@ -1008,7 +1028,7 @@ 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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