[PATCH 01/13] block/file-posix: drop the XFS workaround for post-EOF fallocate

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

292d06b925b extended the tracked request of a post-EOF write zeroes to
infinity and made it serialising, to work around an XFS bug where AIO
writes past EOF were discarded by a concurrently extending fallocate().

The kernel bug was fixed by 249bd9087a52 ("xfs: properly serialise
fallocate against AIO+DIO"), which moves inode_dio_wait() up under
IOLOCK_EXCL so fallocate cannot run alongside in-flight AIO. That
landed in v5.5, three days before the workaround was committed here,
and predates every stable series still maintained.

The workaround runs on every filesystem and on every write zeroes past
EOF, which for the preallocate filter is every preallocation. It widens
the request to the end of the address space and makes it serialising,
so it excludes every other request above its offset, and it does that
after bdrv_co_write_req_prepare() has honoured BDRV_REQ_NO_WAIT, so the
flag no longer holds for the rest of the request.

Drop it. The only series that never took the kernel fix is 4.19.y,
which is end of life.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Cc: qemu-stable@nongnu.org
CC: Kevin Wolf <kwolf@redhat.com>
CC: Hanna Reitz <hreitz@redhat.com>
CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
CC: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 block/file-posix.c | 34 ----------------------------------
 1 file changed, 34 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 9aad156aad..529e302041 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -3658,40 +3658,6 @@ raw_do_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes,
     RawPosixAIOData acb;
     ThreadPoolFunc *handler;
 
-#ifdef CONFIG_FALLOCATE
-    if (offset + bytes > bs->total_sectors * BDRV_SECTOR_SIZE) {
-        BdrvTrackedRequest *req;
-
-        /*
-         * This is a workaround for a bug in the Linux XFS driver,
-         * where writes submitted through the AIO interface will be
-         * discarded if they happen beyond a concurrently running
-         * fallocate() that increases the file length (i.e., both the
-         * write and the fallocate() happen beyond the EOF).
-         *
-         * To work around it, we extend the tracked request for this
-         * zero write until INT64_MAX (effectively infinity), and mark
-         * it as serializing.
-         *
-         * We have to enable this workaround for all filesystems and
-         * AIO modes (not just XFS with aio=native), because for
-         * remote filesystems we do not know the host configuration.
-         */
-
-        req = bdrv_co_get_self_request(bs);
-        assert(req);
-        assert(req->type == BDRV_TRACKED_WRITE);
-        assert(req->offset <= offset);
-        assert(req->offset + req->bytes >= offset + bytes);
-
-        req->bytes = BDRV_MAX_LENGTH - req->offset;
-
-        bdrv_check_request(req->offset, req->bytes, &error_abort);
-
-        bdrv_make_request_serialising(req, bs->bl.request_alignment);
-    }
-#endif
-
     acb = (RawPosixAIOData) {
         .bs             = bs,
         .aio_fildes     = s->fd,
-- 
2.53.0