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From f17b37b58a57d849d2ff5fa04f149d9415803a39 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Wed, 8 Apr 2020 17:29:17 +0100
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Subject: [PATCH 6/6] block: Fix blk->in_flight during blk_wait_while_drained()
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20200408172917.18712-7-kwolf@redhat.com>
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Patchwork-id: 94599
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O-Subject: [RHEL-AV-8.2.0 qemu-kvm PATCH 6/6] block: Fix blk->in_flight during blk_wait_while_drained()
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Bugzilla: 1817621
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RH-Acked-by: Eric Blake <eblake@redhat.com>
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RH-Acked-by: Danilo de Paula <ddepaula@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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Waiting in blk_wait_while_drained() while blk->in_flight is increased
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for the current request is wrong because it will cause the drain
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operation to deadlock.
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This patch makes sure that blk_wait_while_drained() is called with
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blk->in_flight increased exactly once for the current request, and that
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it temporarily decreases the counter while it waits.
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Fixes: cf3129323f900ef5ddbccbe86e4fa801e88c566e
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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Reviewed-by: Max Reitz <mreitz@redhat.com>
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Message-Id: <20200407121259.21350-4-kwolf@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit 7f16476fab14fc32388e0ebae793f64673848efa)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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block/block-backend.c | 17 +++++------------
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1 file changed, 5 insertions(+), 12 deletions(-)
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diff --git a/block/block-backend.c b/block/block-backend.c
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index 610dbfa..38ae413 100644
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--- a/block/block-backend.c
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+++ b/block/block-backend.c
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@@ -1140,10 +1140,15 @@ static int blk_check_byte_request(BlockBackend *blk, int64_t offset,
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return 0;
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}
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+/* To be called between exactly one pair of blk_inc/dec_in_flight() */
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static void coroutine_fn blk_wait_while_drained(BlockBackend *blk)
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{
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+ assert(blk->in_flight > 0);
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+
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if (blk->quiesce_counter && !blk->disable_request_queuing) {
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+ blk_dec_in_flight(blk);
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qemu_co_queue_wait(&blk->queued_requests, NULL);
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+ blk_inc_in_flight(blk);
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}
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}
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@@ -1418,12 +1423,6 @@ static void blk_aio_read_entry(void *opaque)
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BlkRwCo *rwco = &acb->rwco;
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QEMUIOVector *qiov = rwco->iobuf;
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- if (rwco->blk->quiesce_counter) {
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- blk_dec_in_flight(rwco->blk);
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- blk_wait_while_drained(rwco->blk);
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- blk_inc_in_flight(rwco->blk);
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- }
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-
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assert(qiov->size == acb->bytes);
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rwco->ret = blk_do_preadv(rwco->blk, rwco->offset, acb->bytes,
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qiov, rwco->flags);
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@@ -1436,12 +1435,6 @@ static void blk_aio_write_entry(void *opaque)
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BlkRwCo *rwco = &acb->rwco;
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QEMUIOVector *qiov = rwco->iobuf;
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- if (rwco->blk->quiesce_counter) {
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- blk_dec_in_flight(rwco->blk);
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- blk_wait_while_drained(rwco->blk);
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- blk_inc_in_flight(rwco->blk);
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- }
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-
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assert(!qiov || qiov->size == acb->bytes);
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rwco->ret = blk_do_pwritev_part(rwco->blk, rwco->offset, acb->bytes,
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qiov, 0, rwco->flags);
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--
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1.8.3.1
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