ext4: update direct I/O read lock pattern for IOCB_NOWAIT

[ Upstream commit 548feebec7e93e58b647dba70b3303dcb569c914 ]

This patch updates the lock pattern in ext4_direct_IO_read() to not
block on inode lock in cases of IOCB_NOWAIT direct I/O reads. The
locking condition implemented here is similar to that of 942491c9e6d6
("xfs: fix AIM7 regression").

Fixes: 16c54688592c ("ext4: Allow parallel DIO reads")
Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/c5d5e759f91747359fbd2c6f9a36240cf75ad79f.1572949325.git.mbobrowski@mbobrowski.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 215802c..00d0c4b 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3848,7 +3848,13 @@ static ssize_t ext4_direct_IO_read(struct kiocb *iocb, struct iov_iter *iter)
         * writes & truncates and since we take care of writing back page cache,
         * we are protected against page writeback as well.
         */
-       inode_lock_shared(inode);
+       if (iocb->ki_flags & IOCB_NOWAIT) {
+               if (!inode_trylock_shared(inode))
+                       return -EAGAIN;
+       } else {
+               inode_lock_shared(inode);
+       }
+
        ret = filemap_write_and_wait_range(mapping, iocb->ki_pos,
                                           iocb->ki_pos + count - 1);
        if (ret)