Messages in this thread | | | Subject | Re: [RFC PATCH v2 2/2] blk-mq: Lockout tagset iter when freeing rqs | From | Bart Van Assche <> | Date | Tue, 22 Dec 2020 08:16:59 -0800 |
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On 12/22/20 3:15 AM, John Garry wrote: > So then we could have something like this: > > ---8<--- > > -435,9 +444,13 @@ void blk_mq_queue_tag_busy_iter(struct request_queue > *q, busy_iter_fn *fn, > if (!blk_mq_hw_queue_mapped(hctx)) > continue; > > + while (!atomic_inc_not_zero(&tags->iter_usage_counter)); > + > if (tags->nr_reserved_tags) > bt_for_each(hctx, tags->breserved_tags, fn, priv, true); > bt_for_each(hctx, tags->bitmap_tags, fn, priv, false); > > + atomic_dec(&tags->iter_usage_counter); > } > > blk_queue_exit(q); > > --->8--- > > And similar for blk_mq_tagset_busy_iter(). How about it?
Are there any blk_mq_tagset_busy_iter() calls that happen from a context where the tag set can disappear while that function is in progress?
Some blk_mq_tagset_busy_iter() calls happen from a context where it is not allowed to sleep but also where it is guaranteed that the tag set won't disappear, e.g. the call from inside sdk_mq_queue_rq().
How about using a mutex inside blk_mq_queue_tag_busy_iter() instead? As far as I can see all blk_mq_queue_tag_busy_iter() happen from a context where it is allowed to sleep.
Thanks,
Bart.
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