ext4: use i_mutex to serialize unaligned AIO DIO
Currently we've used hashed aio_mutex to serialize unaligned AIO DIO.
However the code cleanups that happened after 2011 when the lock was
introduced made aio_mutex acquired at almost the same places where we
already have exclusion using i_mutex. So just use i_mutex for the
exclusion of unaligned AIO DIO.
The change moves waiting for pending unwritten extent conversion under
i_mutex. That makes special handling of O_APPEND writes unnecessary and
also avoids possible livelocking of unaligned AIO DIO with aligned one
(nothing was preventing contiguous stream of aligned AIO DIOs to let
unaligned AIO DIO wait forever).
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 474f1a4..4a11535 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -93,32 +93,30 @@
{
struct file *file = iocb->ki_filp;
struct inode *inode = file_inode(iocb->ki_filp);
- struct mutex *aio_mutex = NULL;
struct blk_plug plug;
int o_direct = iocb->ki_flags & IOCB_DIRECT;
+ int unaligned_aio = 0;
int overwrite = 0;
ssize_t ret;
- /*
- * Unaligned direct AIO must be serialized; see comment above
- * In the case of O_APPEND, assume that we must always serialize
- */
- if (o_direct &&
- ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
- !is_sync_kiocb(iocb) &&
- (iocb->ki_flags & IOCB_APPEND ||
- ext4_unaligned_aio(inode, from, iocb->ki_pos))) {
- aio_mutex = ext4_aio_mutex(inode);
- mutex_lock(aio_mutex);
- ext4_unwritten_wait(inode);
- }
-
inode_lock(inode);
ret = generic_write_checks(iocb, from);
if (ret <= 0)
goto out;
/*
+ * Unaligned direct AIO must be serialized among each other as zeroing
+ * of partial blocks of two competing unaligned AIOs can result in data
+ * corruption.
+ */
+ if (o_direct && ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
+ !is_sync_kiocb(iocb) &&
+ ext4_unaligned_aio(inode, from, iocb->ki_pos)) {
+ unaligned_aio = 1;
+ ext4_unwritten_wait(inode);
+ }
+
+ /*
* If we have encountered a bitmap-format file, the size limit
* is smaller than s_maxbytes, which is for extent-mapped files.
*/
@@ -139,7 +137,7 @@
blk_start_plug(&plug);
/* check whether we do a DIO overwrite or not */
- if (ext4_should_dioread_nolock(inode) && !aio_mutex &&
+ if (ext4_should_dioread_nolock(inode) && !unaligned_aio &&
!file->f_mapping->nrpages && pos + length <= i_size_read(inode)) {
struct ext4_map_blocks map;
unsigned int blkbits = inode->i_blkbits;
@@ -181,14 +179,10 @@
if (o_direct)
blk_finish_plug(&plug);
- if (aio_mutex)
- mutex_unlock(aio_mutex);
return ret;
out:
inode_unlock(inode);
- if (aio_mutex)
- mutex_unlock(aio_mutex);
return ret;
}