linux-ext4 - [PATCH v6 02/11] ext4: update direct I/O read lock pattern for IOCB

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Message-ID: <17824b863511c87c3b4ea36531ca3c1430d30660.1572255425.git.mbobrowski@mbobrowski.org>
Date:   Mon, 28 Oct 2019 21:50:54 +1100
From:   Matthew Bobrowski <mbobrowski@...browski.org>
To:     tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: [PATCH v6 02/11] ext4: update direct I/O read lock pattern for
 IOCB_NOWAIT

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@...browski.org>
Reviewed-by: Jan Kara <jack@...e.cz>
Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
---
 fs/ext4/inode.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ee116344c420..0a9ea291cfab 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3837,7 +3837,13 @@ 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)
-- 
2.20.1