From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55751) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fayyU-0008Up-EM for qemu-devel@nongnu.org; Thu, 05 Jul 2018 03:46:48 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fayyR-0001m9-Dx for qemu-devel@nongnu.org; Thu, 05 Jul 2018 03:46:46 -0400 From: Vladimir Sementsov-Ogievskiy Date: Thu, 5 Jul 2018 10:46:35 +0300 Message-Id: <20180705074638.770905-2-vsementsov@virtuozzo.com> In-Reply-To: <20180705074638.770905-1-vsementsov@virtuozzo.com> References: <20180705074638.770905-1-vsementsov@virtuozzo.com> Subject: [Qemu-devel] [PATCH v3 1/4] block: disallow BDRV_REQ_NO_SERIALISING for write List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, qemu-block@nongnu.org Cc: pl@kamp.de, pbonzini@redhat.com, ronniesahlberg@gmail.com, famz@redhat.com, stefanha@redhat.com, mreitz@redhat.com, kwolf@redhat.com, jcody@redhat.com, jsnow@redhat.com, den@openvz.org, vsementsov@virtuozzo.com Before commit 9ded4a01149 "backup: Use copy offloading", BDRV_REQ_NO_SERIALISING was used for only one case: read in copy-on-write operation during backup. Also, the flag was handled only on read path (in bdrv_co_preadv and bdrv_aligned_preadv). After 9ded4a01149, flag is used for not waiting serializing operations on backup target (in same case of copy-on-write operation). This behavior change is unsubstantiated and potentially dangerous, let's drop it. Signed-off-by: Vladimir Sementsov-Ogievskiy --- include/block/block.h | 13 +++++++++++++ block/io.c | 7 ++++++- 2 files changed, 19 insertions(+), 1 deletion(-) diff --git a/include/block/block.h b/include/block/block.h index e5c7759a0c..a06a4d27de 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -50,6 +50,19 @@ typedef enum { * opened with BDRV_O_UNMAP. */ BDRV_REQ_MAY_UNMAP = 0x4, + + /* The BDRV_REQ_NO_SERIALISING means that we don't want to + * wait_serialising_requests(), when reading. + * + * This flag is used for backup copy on write operation, when we need to + * read old data before write (write notifier triggered). It is ok, due to + * we already waited for serializing requests in initiative write (see + * bdrv_aligned_pwritev), and it is necessary for the case when initiative + * write is serializing itself (we'll dead lock waiting it). + * + * The described case is the only usage for the flag for now, so, it is + * supported only for read operation and restricted for write. + */ BDRV_REQ_NO_SERIALISING = 0x8, BDRV_REQ_FUA = 0x10, BDRV_REQ_WRITE_COMPRESSED = 0x20, diff --git a/block/io.c b/block/io.c index 1a2272fad3..51bef9fc50 100644 --- a/block/io.c +++ b/block/io.c @@ -1572,6 +1572,8 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child, max_transfer = QEMU_ALIGN_DOWN(MIN_NON_ZERO(bs->bl.max_transfer, INT_MAX), align); + /* BDRV_REQ_NO_SERIALISING is only for read operation */ + assert(!(flags & BDRV_REQ_NO_SERIALISING)); waited = wait_serialising_requests(req); assert(!waited || !req->serialising); assert(req->overlap_offset <= offset); @@ -2931,9 +2933,12 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src, bytes, BDRV_TRACKED_WRITE); if (!(flags & BDRV_REQ_NO_SERIALISING)) { + /* BDRV_REQ_NO_SERIALISING is only for read */ wait_serialising_requests(&src_req); - wait_serialising_requests(&dst_req); } + + wait_serialising_requests(&dst_req); + if (recurse_src) { ret = src->bs->drv->bdrv_co_copy_range_from(src->bs, src, src_offset, -- 2.11.1