[PATCH] aio: Fix freeze protection of aio writes

[Jan Kara <jack@suse.cz>]

Currently we dropped freeze protection of aio writes just after IO was
submitted. Thus aio write could be in flight while the filesystem was
frozen and that could result in unexpected situation like aio completion
wanting to convert extent type on frozen filesystem. Testcase from
Dmitry triggering this is like:

for ((i=0;i<60;i++));do fsfreeze -f /mnt ;sleep 1;fsfreeze -u /mnt;done &
fio --bs=4k --ioengine=libaio --iodepth=128 --size=1g --direct=1 \
    --runtime=60 --filename=/mnt/file --name=rand-write --rw=randwrite

Fix the problem by dropping freeze protection only once IO is completed
in aio_complete().

Reported-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/aio.c           | 31 ++++++++++++++++++++++++++++---
 include/linux/fs.h |  1 +
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 155f84253f33..947481e0a691 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1065,6 +1065,19 @@ static void aio_complete(struct kiocb *kiocb, long res, long res2)
 	unsigned tail, pos, head;
 	unsigned long	flags;
 
+	if (kiocb->ki_flags & IOCB_WRITE) {
+		struct file *f = kiocb->ki_filp;
+
+		/*
+		 * Tell lockdep we inherited freeze protection from submission
+		 * thread.
+		 */
+		percpu_rwsem_acquire(
+			&f->f_inode->i_sb->s_writers.rw_sem[SB_FREEZE_WRITE-1],
+			1, _THIS_IP_);
+		file_end_write(f);
+	}
+
 	/*
 	 * Special case handling for sync iocbs:
 	 *  - events go directly into the iocb for fast handling
@@ -1449,13 +1462,25 @@ rw_common:
 
 		len = ret;
 
-		if (rw == WRITE)
+		if (rw == WRITE) {
 			file_start_write(file);
+			req->ki_flags |= IOCB_WRITE;
+		}
 
 		ret = iter_op(req, &iter);
 
-		if (rw == WRITE)
-			file_end_write(file);
+		if (rw == WRITE) {
+			/*
+			 * We release freeze protection in aio_complete(). Fool
+ 			 * lockdep by telling it the lock got released so that
+			 * it doesn't complain about held lock when we return
+			 * to userspace.
+			 */
+			percpu_rwsem_release(
+				&file->f_inode->i_sb->s_writers.rw_sem[SB_FREEZE_WRITE-1],
+				1, _THIS_IP_);
+		}
+
 		kfree(iovec);
 		break;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3aa514254161..54af40ed6a26 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -319,6 +319,7 @@ struct writeback_control;
 #define IOCB_EVENTFD		(1 << 0)
 #define IOCB_APPEND		(1 << 1)
 #define IOCB_DIRECT		(1 << 2)
+#define IOCB_WRITE		(1 << 3)
 
 struct kiocb {
 	struct file		*ki_filp;
-- 
2.1.4