[PATCH 3/5] fs: make BLKFLSBUF's wait for a superblock killable

[Josef Bacik]

fs_bdev_sync() syncs the filesystems on a block device for BLKFLSBUF.  It
can already be killed while it waits for one which is being unmounted.  For
one which is still being mounted it waits for SB_BORN, and then for
s_umount, in super_lock(), which can't be killed.  If the mount is stuck on
that very device, so is the ioctl.

Use super_lock_killable() and stop the walk when the task is killed, as for
the unmount.  All BLKFLSBUF does afterwards is invalidate_bdev(), which
leaves dirty pages and pages under writeback alone.

Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
 fs/super.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 40f92ffa39c1..ecba64ed0c2a 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1676,17 +1676,21 @@ static void fs_bdev_sync(struct block_device *bdev)
 
 	for (sb_dev = super_dev_first(dev); sb_dev; sb_dev = super_dev_next(sb_dev)) {
 		struct super_block *sb = sb_dev->sd_sb;
+		int ret;
 
-		if (!super_lock_shared(sb)) {
-			if (super_wait_shutdown_killable(sb)) {
-				super_dev_put(sb_dev);
-				return;
-			}
+		ret = super_lock_killable(sb, false);
+		if (!ret) {
+			if (sb->s_root && (sb->s_flags & SB_ACTIVE))
+				sync_filesystem(sb);
+			super_unlock_shared(sb);
 			continue;
 		}
-		if (sb->s_root && (sb->s_flags & SB_ACTIVE))
-			sync_filesystem(sb);
-		super_unlock_shared(sb);
+		if (ret == -ENOENT)
+			ret = super_wait_shutdown_killable(sb);
+		if (ret) {
+			super_dev_put(sb_dev);
+			return;
+		}
 	}
 }
 

-- 
2.55.0