author: Paolo Valente <paolo.valente@linaro.org> 2021-05-12 11:43:52 +0200
committer: Jens Axboe <axboe@kernel.dk> 2021-05-12 07:39:23 -0600
commit: 7ea96eefb0097d243af62fc672be9f17b10338b3
parent: e9f4eee9a0023ba22db9560d4cc6ee63f933dae8
Commit Summary:
Diffstat:
1 file changed, 27 insertions, 2 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 59b2499d3f8b..acd1f881273e 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -372,9 +372,38 @@ struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
return bic->bfqq[is_sync];
}
+static void bfq_put_stable_ref(struct bfq_queue *bfqq);
+
void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
{
+ /*
+ * If bfqq != NULL, then a non-stable queue merge between
+ * bic->bfqq and bfqq is happening here. This causes troubles
+ * in the following case: bic->bfqq has also been scheduled
+ * for a possible stable merge with bic->stable_merge_bfqq,
+ * and bic->stable_merge_bfqq == bfqq happens to
+ * hold. Troubles occur because bfqq may then undergo a split,
+ * thereby becoming eligible for a stable merge. Yet, if
+ * bic->stable_merge_bfqq points exactly to bfqq, then bfqq
+ * would be stably merged with itself. To avoid this anomaly,
+ * we cancel the stable merge if
+ * bic->stable_merge_bfqq == bfqq.
+ */
bic->bfqq[is_sync] = bfqq;
+
+ if (bfqq && bic->stable_merge_bfqq == bfqq) {
+ /*
+ * Actually, these same instructions are executed also
+ * in bfq_setup_cooperator, in case of abort or actual
+ * execution of a stable merge. We could avoid
+ * repeating these instructions there too, but if we
+ * did so, we would nest even more complexity in this
+ * function.
+ */
+ bfq_put_stable_ref(bic->stable_merge_bfqq);
+
+ bic->stable_merge_bfqq = NULL;
+ }
}
struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
@@ -2630,8 +2659,6 @@ static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
struct bfq_queue *bfqq);
-static void bfq_put_stable_ref(struct bfq_queue *bfqq);
-
/*
* Attempt to schedule a merge of bfqq with the currently in-service
* queue or with a close queue among the scheduled queues. Return