From: Ming Lei ming.lei@redhat.com
[ Upstream commit bd63141d585bef14f4caf111f6d0e27fe2300ec6 ]
refcount_inc_not_zero() in bt_tags_iter() still may read one freed request.
Fix the issue by the following approach:
1) hold a per-tags spinlock when reading ->rqs[tag] and calling refcount_inc_not_zero in bt_tags_iter()
2) clearing stale request referred via ->rqs[tag] before freeing request pool, the per-tags spinlock is held for clearing stale ->rq[tag]
So after we cleared stale requests, bt_tags_iter() won't observe freed request any more, also the clearing will wait for pending request reference.
The idea of clearing ->rqs[] is borrowed from John Garry's previous patch and one recent David's patch.
Tested-by: John Garry john.garry@huawei.com Reviewed-by: David Jeffery djeffery@redhat.com Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Ming Lei ming.lei@redhat.com Link: https://lore.kernel.org/r/20210511152236.763464-4-ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-mq-tag.c | 9 +++++++-- block/blk-mq-tag.h | 6 ++++++ block/blk-mq.c | 46 +++++++++++++++++++++++++++++++++++++++++----- 3 files changed, 54 insertions(+), 7 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 6772c3728865..c4f2f6c123ae 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -202,10 +202,14 @@ struct bt_iter_data { static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags, unsigned int bitnr) { - struct request *rq = tags->rqs[bitnr]; + struct request *rq; + unsigned long flags;
+ spin_lock_irqsave(&tags->lock, flags); + rq = tags->rqs[bitnr]; if (!rq || !refcount_inc_not_zero(&rq->ref)) - return NULL; + rq = NULL; + spin_unlock_irqrestore(&tags->lock, flags); return rq; }
@@ -538,6 +542,7 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
tags->nr_tags = total_tags; tags->nr_reserved_tags = reserved_tags; + spin_lock_init(&tags->lock);
if (flags & BLK_MQ_F_TAG_HCTX_SHARED) return tags; diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h index 7d3e6b333a4a..f887988e5ef6 100644 --- a/block/blk-mq-tag.h +++ b/block/blk-mq-tag.h @@ -20,6 +20,12 @@ struct blk_mq_tags { struct request **rqs; struct request **static_rqs; struct list_head page_list; + + /* + * used to clear request reference in rqs[] before freeing one + * request pool + */ + spinlock_t lock; };
extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, diff --git a/block/blk-mq.c b/block/blk-mq.c index 50d3527a5d97..00d6ed2fe812 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2276,6 +2276,45 @@ queue_exit: return BLK_QC_T_NONE; }
+static size_t order_to_size(unsigned int order) +{ + return (size_t)PAGE_SIZE << order; +} + +/* called before freeing request pool in @tags */ +static void blk_mq_clear_rq_mapping(struct blk_mq_tag_set *set, + struct blk_mq_tags *tags, unsigned int hctx_idx) +{ + struct blk_mq_tags *drv_tags = set->tags[hctx_idx]; + struct page *page; + unsigned long flags; + + list_for_each_entry(page, &tags->page_list, lru) { + unsigned long start = (unsigned long)page_address(page); + unsigned long end = start + order_to_size(page->private); + int i; + + for (i = 0; i < set->queue_depth; i++) { + struct request *rq = drv_tags->rqs[i]; + unsigned long rq_addr = (unsigned long)rq; + + if (rq_addr >= start && rq_addr < end) { + WARN_ON_ONCE(refcount_read(&rq->ref) != 0); + cmpxchg(&drv_tags->rqs[i], rq, NULL); + } + } + } + + /* + * Wait until all pending iteration is done. + * + * Request reference is cleared and it is guaranteed to be observed + * after the ->lock is released. + */ + spin_lock_irqsave(&drv_tags->lock, flags); + spin_unlock_irqrestore(&drv_tags->lock, flags); +} + void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, unsigned int hctx_idx) { @@ -2294,6 +2333,8 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, } }
+ blk_mq_clear_rq_mapping(set, tags, hctx_idx); + while (!list_empty(&tags->page_list)) { page = list_first_entry(&tags->page_list, struct page, lru); list_del_init(&page->lru); @@ -2353,11 +2394,6 @@ struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set, return tags; }
-static size_t order_to_size(unsigned int order) -{ - return (size_t)PAGE_SIZE << order; -} - static int blk_mq_init_request(struct blk_mq_tag_set *set, struct request *rq, unsigned int hctx_idx, int node) {