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From: Max Reitz <mreitz@redhat.com>
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Subject: [Qemu-devel] [PULL 38/42] job: Avoid deadlocks in
job_completed_txn_abort()
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Cc: Kevin Wolf <kwolf@redhat.com>, Peter Maydell <peter.maydell@linaro.org>,
qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>
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From: Kevin Wolf <kwolf@redhat.com>
Amongst others, job_finalize_single() calls the .prepare/.commit/.abort
callbacks of the individual job driver. Recently, their use was adapted
for all block jobs so that they involve code calling AIO_WAIT_WHILE()
now. Such code must be called under the AioContext lock for the
respective job, but without holding any other AioContext lock.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
job.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/job.c b/job.c
index 518f603314..93aea79a7b 100644
--- a/job.c
+++ b/job.c
@@ -718,6 +718,7 @@ static void job_cancel_async(Job *job, bool force)
=20
static void job_completed_txn_abort(Job *job)
{
+ AioContext *outer_ctx =3D job->aio_context;
AioContext *ctx;
JobTxn *txn =3D job->txn;
Job *other_job;
@@ -731,23 +732,26 @@ static void job_completed_txn_abort(Job *job)
txn->aborting =3D true;
job_txn_ref(txn);
=20
- /* We are the first failed job. Cancel other jobs. */
- QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
- ctx =3D other_job->aio_context;
- aio_context_acquire(ctx);
- }
+ /* We can only hold the single job's AioContext lock while calling
+ * job_finalize_single() because the finalization callbacks can involve
+ * calls of AIO_WAIT_WHILE(), which could deadlock otherwise. */
+ aio_context_release(outer_ctx);
=20
/* Other jobs are effectively cancelled by us, set the status for
* them; this job, however, may or may not be cancelled, depending
* on the caller, so leave it. */
QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
if (other_job !=3D job) {
+ ctx =3D other_job->aio_context;
+ aio_context_acquire(ctx);
job_cancel_async(other_job, false);
+ aio_context_release(ctx);
}
}
while (!QLIST_EMPTY(&txn->jobs)) {
other_job =3D QLIST_FIRST(&txn->jobs);
ctx =3D other_job->aio_context;
+ aio_context_acquire(ctx);
if (!job_is_completed(other_job)) {
assert(job_is_cancelled(other_job));
job_finish_sync(other_job, NULL, NULL);
@@ -756,6 +760,8 @@ static void job_completed_txn_abort(Job *job)
aio_context_release(ctx);
}
=20
+ aio_context_acquire(outer_ctx);
+
job_txn_unref(txn);
}
=20
--=20
2.17.1