[Qemu-devel] [PATCH] job: Fix nested aio_poll() hanging in job_txn_apply

[Fam Zheng]

All callers have acquired ctx already. Doing that again results in
aio_poll() hang. This fixes the problem that a BDRV_POLL_WHILE() in the
callback cannot make progress because ctx is recursively locked, for
example, when drive-backup finishes.

Cc: qemu-sta...@nongnu.org
Reported-by: Gu Nini <n...@redhat.com>
Signed-off-by: Fam Zheng <f...@redhat.com>
---
 job.c | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/job.c b/job.c
index fa671b431a..b07c5d0ffc 100644
--- a/job.c
+++ b/job.c
@@ -136,21 +136,13 @@ static void job_txn_del_job(Job *job)
     }
 }
 
-static int job_txn_apply(JobTxn *txn, int fn(Job *), bool lock)
+static int job_txn_apply(JobTxn *txn, int fn(Job *))
 {
-    AioContext *ctx;
     Job *job, *next;
     int rc = 0;
 
     QLIST_FOREACH_SAFE(job, &txn->jobs, txn_list, next) {
-        if (lock) {
-            ctx = job->aio_context;
-            aio_context_acquire(ctx);
-        }
         rc = fn(job);
-        if (lock) {
-            aio_context_release(ctx);
-        }
         if (rc) {
             break;
         }
@@ -807,11 +799,11 @@ static void job_do_finalize(Job *job)
     assert(job && job->txn);
 
     /* prepare the transaction to complete */
-    rc = job_txn_apply(job->txn, job_prepare, true);
+    rc = job_txn_apply(job->txn, job_prepare);
     if (rc) {
         job_completed_txn_abort(job);
     } else {
-        job_txn_apply(job->txn, job_finalize_single, true);
+        job_txn_apply(job->txn, job_finalize_single);
     }
 }
 
@@ -857,10 +849,10 @@ static void job_completed_txn_success(Job *job)
         assert(other_job->ret == 0);
     }
 
-    job_txn_apply(txn, job_transition_to_pending, false);
+    job_txn_apply(txn, job_transition_to_pending);
 
     /* If no jobs need manual finalization, automatically do so */
-    if (job_txn_apply(txn, job_needs_finalize, false) == 0) {
+    if (job_txn_apply(txn, job_needs_finalize) == 0) {
         job_do_finalize(job);
     }
 }
-- 
2.17.1