80 lines
3.1 KiB
Diff
80 lines
3.1 KiB
Diff
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Wed, 13 Mar 2024 16:30:00 +0100
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Subject: [PATCH] mirror: Don't call job_pause_point() under graph lock
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Calling job_pause_point() while holding the graph reader lock
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potentially results in a deadlock: bdrv_graph_wrlock() first drains
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everything, including the mirror job, which pauses it. The job is only
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unpaused at the end of the drain section, which is when the graph writer
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lock has been successfully taken. However, if the job happens to be
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paused at a pause point where it still holds the reader lock, the writer
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lock can't be taken as long as the job is still paused.
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Mark job_pause_point() as GRAPH_UNLOCKED and fix mirror accordingly.
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Cc: qemu-stable@nongnu.org
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Buglink: https://issues.redhat.com/browse/RHEL-28125
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Fixes: 004915a96a7a ("block: Protect bs->backing with graph_lock")
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Message-ID: <20240313153000.33121-1-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 ae5a40e8581185654a667fbbf7e4adbc2a2a3e45)
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Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
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---
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block/mirror.c | 10 ++++++----
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include/qemu/job.h | 2 +-
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2 files changed, 7 insertions(+), 5 deletions(-)
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diff --git a/block/mirror.c b/block/mirror.c
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index cd9d3ad4a8..abbddb39e4 100644
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--- a/block/mirror.c
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+++ b/block/mirror.c
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@@ -479,9 +479,9 @@ static unsigned mirror_perform(MirrorBlockJob *s, int64_t offset,
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return bytes_handled;
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}
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-static void coroutine_fn GRAPH_RDLOCK mirror_iteration(MirrorBlockJob *s)
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+static void coroutine_fn GRAPH_UNLOCKED mirror_iteration(MirrorBlockJob *s)
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{
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- BlockDriverState *source = s->mirror_top_bs->backing->bs;
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+ BlockDriverState *source;
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MirrorOp *pseudo_op;
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int64_t offset;
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/* At least the first dirty chunk is mirrored in one iteration. */
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@@ -489,6 +489,10 @@ static void coroutine_fn GRAPH_RDLOCK mirror_iteration(MirrorBlockJob *s)
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bool write_zeroes_ok = bdrv_can_write_zeroes_with_unmap(blk_bs(s->target));
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int max_io_bytes = MAX(s->buf_size / MAX_IN_FLIGHT, MAX_IO_BYTES);
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+ bdrv_graph_co_rdlock();
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+ source = s->mirror_top_bs->backing->bs;
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+ bdrv_graph_co_rdunlock();
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+
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bdrv_dirty_bitmap_lock(s->dirty_bitmap);
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offset = bdrv_dirty_iter_next(s->dbi);
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if (offset < 0) {
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@@ -1078,9 +1082,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
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mirror_wait_for_free_in_flight_slot(s);
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continue;
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} else if (cnt != 0) {
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- bdrv_graph_co_rdlock();
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mirror_iteration(s);
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- bdrv_graph_co_rdunlock();
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}
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}
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diff --git a/include/qemu/job.h b/include/qemu/job.h
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index e502787dd8..b4bc2e174b 100644
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--- a/include/qemu/job.h
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+++ b/include/qemu/job.h
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@@ -503,7 +503,7 @@ void job_enter(Job *job);
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*
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* Called with job_mutex *not* held.
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*/
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-void coroutine_fn job_pause_point(Job *job);
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+void coroutine_fn GRAPH_UNLOCKED job_pause_point(Job *job);
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/**
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* @job: The job that calls the function.
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