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authorJiaying Zhang <jiayingz@google.com>2011-08-19 19:13:32 -0400
committerTheodore Ts'o <tytso@mit.edu>2011-08-19 19:13:32 -0400
commitdccaf33fa37a1bc5d651baeb3bfeb6becb86597b (patch)
treeff41c9c0208589fded8176089380e316dd5c7965
parent9dd75f1f1a02d656a11a7b9b9e6c2759b9c1e946 (diff)
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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 <jiayingz@google.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Cc: stable@kernel.org
-rw-r--r--fs/ext4/indirect.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index b8602cde5b5..0962642119c 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);