From 191d44fc4361932c3ae647eee343e150fb8b6e34 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Wed, 14 Jul 2010 12:42:02 +0200 Subject: [PATCH] block: Fix early failure in multiwrite bdrv_aio_writev may call the callback immediately (and it will commonly do so in error cases). Current code doesn't consider this. For details see the comment added by this patch. Signed-off-by: Kevin Wolf (cherry picked from commit 453f9a1652629e5805995b165be2e634c8487139) Conflicts: block.c Signed-off-by: Kevin Wolf --- block.c | 37 ++++++++++++++++++++++++++++++------- 1 file changed, 30 insertions(+), 7 deletions(-) diff --git a/block.c b/block.c index e3b3a5504f..80f2faecdb 100644 --- a/block.c +++ b/block.c @@ -1802,8 +1802,29 @@ int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs) // Check for mergable requests num_reqs = multiwrite_merge(bs, reqs, num_reqs, mcb); - // Run the aio requests + /* + * Run the aio requests. As soon as one request can't be submitted + * successfully, fail all requests that are not yet submitted (we must + * return failure for all requests anyway) + * + * num_requests cannot be set to the right value immediately: If + * bdrv_aio_writev fails for some request, num_requests would be too high + * and therefore multiwrite_cb() would never recognize the multiwrite + * request as completed. We also cannot use the loop variable i to set it + * when the first request fails because the callback may already have been + * called for previously submitted requests. Thus, num_requests must be + * incremented for each request that is submitted. + * + * The problem that callbacks may be called early also means that we need + * to take care that num_requests doesn't become 0 before all requests are + * submitted - multiwrite_cb() would consider the multiwrite request + * completed. A dummy request that is "completed" by a manual call to + * multiwrite_cb() takes care of this. + */ + mcb->num_requests = 1; + for (i = 0; i < num_reqs; i++) { + mcb->num_requests++; acb = bdrv_aio_writev(bs, reqs[i].sector, reqs[i].qiov, reqs[i].nb_sectors, multiwrite_cb, mcb); @@ -1811,23 +1832,25 @@ int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs) // We can only fail the whole thing if no request has been // submitted yet. Otherwise we'll wait for the submitted AIOs to // complete and report the error in the callback. - if (mcb->num_requests == 0) { - reqs[i].error = -EIO; + if (i == 0) { goto fail; } else { - mcb->num_requests++; multiwrite_cb(mcb, -EIO); break; } - } else { - mcb->num_requests++; } } + /* Complete the dummy request */ + multiwrite_cb(mcb, 0); + return 0; fail: - free(mcb); + for (i = 0; i < mcb->num_callbacks; i++) { + reqs[i].error = -EIO; + } + qemu_free(mcb); return -1; } -- GitLab