Re: [RFC PATCH v3 1/3] blk-mq: Clean up references to old requests when freeing rqs
From: Bart Van Assche <bvanassche@acm.org>
Date: 2021-03-06 18:14:14
Also in:
lkml
On 3/5/21 7:14 AM, John Garry wrote:
quoted hunk ↗ jump to hunk
@@ -2296,10 +2296,14 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, for (i = 0; i < tags->nr_tags; i++) { struct request *rq = tags->static_rqs[i]; + int j; if (!rq) continue; set->ops->exit_request(set, rq, hctx_idx); + /* clean up any references which occur in @ref_tags */ + for (j = 0; ref_tags && j < ref_tags->nr_tags; j++) + cmpxchg(&ref_tags->rqs[j], rq, 0); tags->static_rqs[i] = NULL; } }
What prevents blk_mq_tagset_busy_iter() from reading hctx->tags[...] before the cmpxcg() call and dereferencing it after blk_mq_free_rqs() has called __free_pages()? Thanks, Bart.