From ae5a40e8581185654a667fbbf7e4adbc2a2a3e45 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Wed, 13 Mar 2024 16:30:00 +0100 Subject: [PATCH] mirror: Don't call job_pause_point() under graph lock Calling job_pause_point() while holding the graph reader lock potentially results in a deadlock: bdrv_graph_wrlock() first drains everything, including the mirror job, which pauses it. The job is only unpaused at the end of the drain section, which is when the graph writer lock has been successfully taken. However, if the job happens to be paused at a pause point where it still holds the reader lock, the writer lock can't be taken as long as the job is still paused. Mark job_pause_point() as GRAPH_UNLOCKED and fix mirror accordingly. Cc: qemu-stable@nongnu.org Buglink: https://issues.redhat.com/browse/RHEL-28125 Fixes: 004915a96a7a ("block: Protect bs->backing with graph_lock") Signed-off-by: Kevin Wolf Message-ID: <20240313153000.33121-1-kwolf@redhat.com> Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- block/mirror.c | 10 ++++++---- include/qemu/job.h | 2 +- 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/block/mirror.c b/block/mirror.c index 5145eb53e1..1bdce3b657 100644 --- a/block/mirror.c +++ b/block/mirror.c @@ -479,9 +479,9 @@ static unsigned mirror_perform(MirrorBlockJob *s, int64_t offset, return bytes_handled; } -static void coroutine_fn GRAPH_RDLOCK mirror_iteration(MirrorBlockJob *s) +static void coroutine_fn GRAPH_UNLOCKED mirror_iteration(MirrorBlockJob *s) { - BlockDriverState *source = s->mirror_top_bs->backing->bs; + BlockDriverState *source; MirrorOp *pseudo_op; int64_t offset; /* At least the first dirty chunk is mirrored in one iteration. */ @@ -489,6 +489,10 @@ static void coroutine_fn GRAPH_RDLOCK mirror_iteration(MirrorBlockJob *s) bool write_zeroes_ok = bdrv_can_write_zeroes_with_unmap(blk_bs(s->target)); int max_io_bytes = MAX(s->buf_size / MAX_IN_FLIGHT, MAX_IO_BYTES); + bdrv_graph_co_rdlock(); + source = s->mirror_top_bs->backing->bs; + bdrv_graph_co_rdunlock(); + bdrv_dirty_bitmap_lock(s->dirty_bitmap); offset = bdrv_dirty_iter_next(s->dbi); if (offset < 0) { @@ -1066,9 +1070,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp) mirror_wait_for_free_in_flight_slot(s); continue; } else if (cnt != 0) { - bdrv_graph_co_rdlock(); mirror_iteration(s); - bdrv_graph_co_rdunlock(); } } diff --git a/include/qemu/job.h b/include/qemu/job.h index 9ea98b5927..2b873f2576 100644 --- a/include/qemu/job.h +++ b/include/qemu/job.h @@ -483,7 +483,7 @@ void job_enter(Job *job); * * Called with job_mutex *not* held. */ -void coroutine_fn job_pause_point(Job *job); +void coroutine_fn GRAPH_UNLOCKED job_pause_point(Job *job); /** * @job: The job that calls the function.