diff options
| -rw-r--r-- | block/cfq-iosched.c | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 002c0cee0b3..4fab7c9df71 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1930,6 +1930,15 @@ static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq) int process_refs, new_process_refs; struct cfq_queue *__cfqq; + /* + * If there are no process references on the new_cfqq, then it is + * unsafe to follow the ->new_cfqq chain as other cfqq's in the + * chain may have dropped their last reference (not just their + * last process reference). + */ + if (!cfqq_process_refs(new_cfqq)) + return; + /* Avoid a circular list and skip interim queue merges */ while ((__cfqq = new_cfqq->new_cfqq)) { if (__cfqq == cfqq) @@ -1938,17 +1947,17 @@ static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq) } process_refs = cfqq_process_refs(cfqq); + new_process_refs = cfqq_process_refs(new_cfqq); /* * If the process for the cfqq has gone away, there is no * sense in merging the queues. */ - if (process_refs == 0) + if (process_refs == 0 || new_process_refs == 0) return; /* * Merge in the direction of the lesser amount of work. */ - new_process_refs = cfqq_process_refs(new_cfqq); if (new_process_refs >= process_refs) { cfqq->new_cfqq = new_cfqq; atomic_add(process_refs, &new_cfqq->ref); |