From: Jiaying Zhang Date: Fri, 19 Aug 2011 23:13:32 +0000 (-0400) Subject: ext4: flush any pending end_io requests before DIO reads w/dioread_nolock X-Git-Tag: firefly_0821_release~3680^2~4609^2 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=dccaf33fa37a1bc5d651baeb3bfeb6becb86597b;p=firefly-linux-kernel-4.4.55.git ext4: flush any pending end_io requests before DIO reads w/dioread_nolock There is a race between ext4 buffer write and direct_IO read with dioread_nolock mount option enabled. The problem is that we clear PageWriteback flag during end_io time but will do uninitialized-to-initialized extent conversion later with dioread_nolock. If an O_direct read request comes in during this period, ext4 will return zero instead of the recently written data. This patch checks whether there are any pending uninitialized-to-initialized extent conversion requests before doing O_direct read to close the race. Note that this is just a bandaid fix. The fundamental issue is that we clear PageWriteback flag before we really complete an IO, which is problem-prone. To fix the fundamental issue, we may need to implement an extent tree cache that we can use to look up pending to-be-converted extents. Signed-off-by: Jiaying Zhang Signed-off-by: "Theodore Ts'o" Cc: stable@kernel.org --- diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c index b8602cde5b5a..0962642119c0 100644 --- a/fs/ext4/indirect.c +++ b/fs/ext4/indirect.c @@ -800,12 +800,17 @@ ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb, } retry: - if (rw == READ && ext4_should_dioread_nolock(inode)) + if (rw == READ && ext4_should_dioread_nolock(inode)) { + if (unlikely(!list_empty(&ei->i_completed_io_list))) { + mutex_lock(&inode->i_mutex); + ext4_flush_completed_IO(inode); + mutex_unlock(&inode->i_mutex); + } ret = __blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov, offset, nr_segs, ext4_get_block, NULL, NULL, 0); - else { + } else { ret = blockdev_direct_IO(rw, iocb, inode, iov, offset, nr_segs, ext4_get_block);