[Devel] [PATCH RHEL7 COMMIT] direct-io: fix AIO regression

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1127.8.2.vz7.161.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.8.2.vz7.161.1
------>
commit ee50772e89aff946f9266a9d3ce49340dbc28abd
Author: Christoph Hellwig <hch at lst.de>
Date:   Mon May 25 17:52:26 2020 +0300

    direct-io: fix AIO regression
    
    ms commit af436472772d
    
    The direct-io.c rewrite to use the iov_iter infrastructure stopped updating
    the size field in struct dio_submit, and thus rendered the check for
    allowing asynchronous completions to always return false.  Fix this by
    comparing it to the count of bytes in the iov_iter instead.
    
    Signed-off-by: Christoph Hellwig <hch at lst.de>
    Reported-by: Tim Chen <tim.c.chen at linux.intel.com>
    Tested-by: Tim Chen <tim.c.chen at linux.intel.com>
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    =====================
    Patchset description:
    [00/30] fs,direct_IO: Switch to iov_iter and allow bio_vec for ext4
    
    This patchset transforms direct_IO callbacks, blockdev_direct_IO
    and its underlining functions to iov_iter, and introduces complete
    support of iov_iter for ext4.
    
    Supported iov_iter subtypes for ext4 is iovec and bio_vec. The first
    is for traditional user-submitted aio, while bio_vec is the type,
    which is important for us, since we use it in ploop.
    
    bio_vec operates with pages instead of user addresses (like iovec
    does), so it requires specific callbacks in do_blockdev_direct_IO()
    and in the functions it calls.
    
    The patchset reworks do_blockdev_direct_IO() in the same manner
    as in mainstrean. The most of rest patches are prepared manually,
    since we have significant differences to ms (RHEL7 patches, our
    direct IO patches for FUSE; all they have changed many functions).
    At the end, kaio engine (resulting in direct_IO) became possible
    to be enabled for ext4.
    
    https://jira.sw.ru/browse/PSBM-99793
---
 fs/direct-io.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 6f0678619939a..55c40be5a0140 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -78,7 +78,6 @@ struct dio_submit {
 					   been performed at the start of a
 					   write */
 	int pages_in_io;		/* approximate total IO pages */
-	size_t	size;			/* total request size (doesn't change)*/
 	sector_t block_in_file;		/* Current offset into the underlying
 					   file in dio_block units. */
 	unsigned blocks_available;	/* At block_in_file.  changes */
@@ -1191,7 +1190,8 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	unsigned blkbits = i_blkbits;
 	unsigned blocksize_mask = (1 << blkbits) - 1;
 	ssize_t retval = -EINVAL;
-	loff_t end = offset + iov_iter_count(iter);
+	size_t count = iov_iter_count(iter);
+	loff_t end = offset + count;
 	struct dio *dio;
 	struct dio_submit sdio = { 0, };
 	unsigned long user_addr;
@@ -1403,10 +1403,9 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	 */
 	BUG_ON(retval == -EIOCBQUEUED);
 	if (dio->is_async && retval == 0 && dio->result &&
-	    ((rw == READ) || (dio->result == sdio.size)))
+	    (rw == READ || dio->result == count))
 		retval = -EIOCBQUEUED;
-
-	if (retval != -EIOCBQUEUED)
+	else
 		dio_await_completion(dio);
 
 	if (drop_refcount(dio) == 0) {