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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
This commit is contained in:
Jiaying Zhang 2011-08-19 19:13:32 -04:00 committed by Theodore Ts'o
parent 9dd75f1f1a
commit dccaf33fa3
1 changed files with 7 additions and 2 deletions
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9
fs/ext4/indirect.c
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@ -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);