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From bddf389330e11fb0ce17413c1bfa2264a281ded2 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Mon, 30 Mar 2020 11:19:24 +0100
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Subject: [PATCH 4/4] mirror: Wait only for in-flight operations
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20200330111924.22938-3-kwolf@redhat.com>
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Patchwork-id: 94463
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O-Subject: [RHEL-AV-8.2.0 qemu-kvm PATCH 2/2] mirror: Wait only for in-flight operations
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Bugzilla: 1794692
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RH-Acked-by: Maxim Levitsky <mlevitsk@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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mirror_wait_for_free_in_flight_slot() just picks a random operation to
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wait for. However, a MirrorOp is already in s->ops_in_flight when
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mirror_co_read() waits for free slots, so if not enough slots are
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immediately available, an operation can end up waiting for itself, or
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two or more operations can wait for each other to complete, which
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results in a hang.
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Fix this by adding a flag to MirrorOp that tells us if the request is
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already in flight (and therefore occupies slots that it will later
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free), and picking only such operations for waiting.
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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1794692
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Message-Id: <20200326153628.4869-3-kwolf@redhat.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit ce8cabbd17cf738ddfc68384440c38e5dd2fdf97)
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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/mirror.c | 9 ++++++++-
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1 file changed, 8 insertions(+), 1 deletion(-)
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diff --git a/block/mirror.c b/block/mirror.c
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index 8959e42..5e5a521 100644
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--- a/block/mirror.c
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+++ b/block/mirror.c
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@@ -102,6 +102,7 @@ struct MirrorOp {
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bool is_pseudo_op;
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bool is_active_write;
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+ bool is_in_flight;
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CoQueue waiting_requests;
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Coroutine *co;
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@@ -293,7 +294,9 @@ mirror_wait_for_any_operation(MirrorBlockJob *s, bool active)
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* caller of this function. Since there is only one pseudo op
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* at any given time, we will always find some real operation
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* to wait on. */
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- if (!op->is_pseudo_op && op->is_active_write == active) {
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+ if (!op->is_pseudo_op && op->is_in_flight &&
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+ op->is_active_write == active)
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+ {
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qemu_co_queue_wait(&op->waiting_requests, NULL);
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return;
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}
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@@ -367,6 +370,7 @@ static void coroutine_fn mirror_co_read(void *opaque)
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/* Copy the dirty cluster. */
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s->in_flight++;
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s->bytes_in_flight += op->bytes;
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+ op->is_in_flight = true;
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trace_mirror_one_iteration(s, op->offset, op->bytes);
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ret = bdrv_co_preadv(s->mirror_top_bs->backing, op->offset, op->bytes,
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@@ -382,6 +386,7 @@ static void coroutine_fn mirror_co_zero(void *opaque)
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op->s->in_flight++;
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op->s->bytes_in_flight += op->bytes;
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*op->bytes_handled = op->bytes;
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+ op->is_in_flight = true;
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ret = blk_co_pwrite_zeroes(op->s->target, op->offset, op->bytes,
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op->s->unmap ? BDRV_REQ_MAY_UNMAP : 0);
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@@ -396,6 +401,7 @@ static void coroutine_fn mirror_co_discard(void *opaque)
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op->s->in_flight++;
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op->s->bytes_in_flight += op->bytes;
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*op->bytes_handled = op->bytes;
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+ op->is_in_flight = true;
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ret = blk_co_pdiscard(op->s->target, op->offset, op->bytes);
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mirror_write_complete(op, ret);
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@@ -1306,6 +1312,7 @@ static MirrorOp *coroutine_fn active_write_prepare(MirrorBlockJob *s,
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.offset = offset,
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.bytes = bytes,
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.is_active_write = true,
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+ .is_in_flight = true,
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};
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qemu_co_queue_init(&op->waiting_requests);
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QTAILQ_INSERT_TAIL(&s->ops_in_flight, op, next);
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--
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1.8.3.1
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