block: Try to handle busy underlying device on discard

BugLink: https://bugs.launchpad.net/bugs/1919492
commit 56887cffe946bb0a90c74429fa94d6110a73119d upstream.

Commit 384d87ef2c95 ("block: Do not discard buffers under a mounted
filesystem") made paths issuing discard or zeroout requests to the
underlying device try to grab block device in exclusive mode. If that
failed we returned EBUSY to userspace. This however caused unexpected
fallout in userspace where e.g. FUSE filesystems issue discard requests
from userspace daemons although the device is open exclusively by the
kernel. Also shrinking of logical volume by LVM issues discard requests
to a device which may be claimed exclusively because there's another LV
on the same PV. So to avoid these userspace regressions, fall back to
invalidate_inode_pages2_range() instead of returning EBUSY to userspace
and return EBUSY only of that call fails as well (meaning that there's
indeed someone using the particular device range we are trying to
discard).

Link: https://bugzilla.kernel.org/show_bug.cgi?id=211167
Fixes: 384d87ef2c95 ("block: Do not discard buffers under a mounted filesystem")
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 235b5042672e9f15cd137c22965eaa3aae9f3f61..c33151020bcd7deafbc2baa808b7d464f7ed3777 100644 (file)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -118,13 +118,22 @@ int truncate_bdev_range(struct block_device *bdev, fmode_t mode,
        if (!(mode & FMODE_EXCL)) {
                int err = bd_prepare_to_claim(bdev, truncate_bdev_range);
                if (err)
-                       return err;
+                       goto invalidate;
        }
 
        truncate_inode_pages_range(bdev->bd_inode->i_mapping, lstart, lend);
        if (!(mode & FMODE_EXCL))
                bd_abort_claiming(bdev, truncate_bdev_range);
        return 0;
+
+invalidate:
+       /*
+        * Someone else has handle exclusively open. Try invalidating instead.
+        * The 'end' argument is inclusive so the rounding is safe.
+        */
+       return invalidate_inode_pages2_range(bdev->bd_inode->i_mapping,
+                                            lstart >> PAGE_SHIFT,
+                                            lend >> PAGE_SHIFT);
 }
 EXPORT_SYMBOL(truncate_bdev_range);