From patchwork Fri Jul 12 09:46:16 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrey Drobyshev X-Patchwork-Id: 13731542 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A6013C2BD09 for ; Fri, 12 Jul 2024 09:47:25 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sSCrU-0002c3-Uw; Fri, 12 Jul 2024 05:46:44 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sSCrF-0002JP-5G; Fri, 12 Jul 2024 05:46:37 -0400 Received: from relay.virtuozzo.com ([130.117.225.111]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sSCrB-0001Y7-Iy; Fri, 12 Jul 2024 05:46:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=virtuozzo.com; s=relay; h=MIME-Version:Message-Id:Date:Subject:From: Content-Type; bh=SxnnQcf/vCqlj8mFGAhTZWtk/V3Dt/KLf3GRTXyVbiM=; b=ee++AjLfkr+e 7lB0d8+Op2frbeK6axigxz5f+LITkVCPmIUmUACjZE+Up1MHLrs9jI6ZT0vmrHlgQ+SBW8ncAsfJc ROxjgaS2AwPsLZncm7LruujMYI4oSaLJyR78XOZCFveR+Yuko0C0D6HsAVtmrXEcO/Zuf9U/4uXNL nMeu62lCPOjDXrlVqDwKVmarqXvYZt0Jj22+IN29S4qioREpA7B/yXgP1iS3hhkliUs9rt9Thirq/ zpNjoNjK8LdHGgV6yAK0++U8RxQRDuZzMquxHbsZo9X8Jmv7BEXpQ5oIHF/D3vMClIQgaMtsw0TzR dhalwBhd6ZYQbKa4SAyCfQ==; Received: from [130.117.225.1] (helo=dev005.ch-qa.vzint.dev) by relay.virtuozzo.com with esmtp (Exim 4.96) (envelope-from ) id 1sSCqO-00Ceua-2b; Fri, 12 Jul 2024 11:46:17 +0200 From: Andrey Drobyshev To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, hreitz@redhat.com, kwolf@redhat.com, vsementsov@yandex-team.ru, pbonzini@redhat.com, eesposit@redhat.com, andrey.drobyshev@virtuozzo.com, den@virtuozzo.com Subject: [PATCH v2 1/2] block: zero data data corruption using prealloc-filter Date: Fri, 12 Jul 2024 12:46:16 +0300 Message-Id: <20240712094617.565237-2-andrey.drobyshev@virtuozzo.com> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20240712094617.565237-1-andrey.drobyshev@virtuozzo.com> References: <20240712094617.565237-1-andrey.drobyshev@virtuozzo.com> MIME-Version: 1.0 Received-SPF: pass client-ip=130.117.225.111; envelope-from=andrey.drobyshev@virtuozzo.com; helo=relay.virtuozzo.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: "Denis V. Lunev" We have observed that some clusters in the QCOW2 files are zeroed while preallocation filter is used. We are able to trace down the following sequence when prealloc-filter is used: co=0x55e7cbed7680 qcow2_co_pwritev_task() co=0x55e7cbed7680 preallocate_co_pwritev_part() co=0x55e7cbed7680 handle_write() co=0x55e7cbed7680 bdrv_co_do_pwrite_zeroes() co=0x55e7cbed7680 raw_do_pwrite_zeroes() co=0x7f9edb7fe500 do_fallocate() Here coroutine 0x55e7cbed7680 is being blocked waiting while coroutine 0x7f9edb7fe500 will finish with fallocate of the file area. OK. It is time to handle next coroutine, which co=0x55e7cbee91b0 qcow2_co_pwritev_task() co=0x55e7cbee91b0 preallocate_co_pwritev_part() co=0x55e7cbee91b0 handle_write() co=0x55e7cbee91b0 bdrv_co_do_pwrite_zeroes() co=0x55e7cbee91b0 raw_do_pwrite_zeroes() co=0x7f9edb7deb00 do_fallocate() The trouble comes here. Coroutine 0x55e7cbed7680 has not advanced file_end yet and coroutine 0x55e7cbee91b0 will start fallocate() for the same area. This means that if (once fallocate is started inside 0x7f9edb7deb00) original fallocate could end and the real write will be executed. In that case write() request is handled at the same time as fallocate(). The patch moves s->file_lock assignment before fallocate and that is crucial. The idea is that all subsequent requests into the area being preallocation will be issued as just writes without fallocate to this area and they will not proceed thanks to overlapping requests mechanics. If preallocation will fail, we will just switch to the normal expand-by-write behavior and that is not a problem except performance. Signed-off-by: Denis V. Lunev Tested-by: Andrey Drobyshev --- block/preallocate.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/block/preallocate.c b/block/preallocate.c index d215bc5d6d..ecf0aa4baa 100644 --- a/block/preallocate.c +++ b/block/preallocate.c @@ -383,6 +383,13 @@ handle_write(BlockDriverState *bs, int64_t offset, int64_t bytes, want_merge_zero = want_merge_zero && (prealloc_start <= offset); + /* + * Assign file_end before making actual preallocation. This will ensure + * that next request performed while preallocation is in progress will + * be passed without preallocation. + */ + s->file_end = prealloc_end; + ret = bdrv_co_pwrite_zeroes( bs->file, prealloc_start, prealloc_end - prealloc_start, BDRV_REQ_NO_FALLBACK | BDRV_REQ_SERIALISING | BDRV_REQ_NO_WAIT); @@ -391,7 +398,6 @@ handle_write(BlockDriverState *bs, int64_t offset, int64_t bytes, return false; } - s->file_end = prealloc_end; return want_merge_zero; }