On 9/22/21 2:10 AM, Adrian Hunter wrote:
The UFS driver uses blk_mq_tagset_busy_iter() when identifying task
management requests to complete, however blk_mq_tagset_busy_iter()
doesn't work.
blk_mq_tagset_busy_iter() only iterates requests dispatched by the block
layer. That appears as if it might have started since commit 37f4a24c2469a1
("blk-mq: centralise related handling into blk_mq_get_driver_tag") which
removed 'data->hctx->tags->rqs[rq->tag] = rq' from blk_mq_rq_ctx_init()
which gets called:
blk_get_request
blk_mq_alloc_request
__blk_mq_alloc_request
blk_mq_rq_ctx_init
Since UFS task management requests are not dispatched by the block
layer, hctx->tags->rqs[rq->tag] remains NULL, and since
blk_mq_tagset_busy_iter() relies on finding requests using
hctx->tags->rqs[rq->tag], UFS task management requests are never found by
blk_mq_tagset_busy_iter().
By using blk_mq_tagset_busy_iter(), the UFS driver was relying on internal
details of the block layer, which was fragile and subsequently got
broken. Fix by removing the use of blk_mq_tagset_busy_iter() and having
the driver keep track of task management requests.
Thanks for the detailed analysis. I agree that using blk_mq_tagset_busy_iter()
no longer works due to recent changes in the block layer. Has it been
considered to export blk_mq_all_tag_iter() and to use that function instead of
blk_mq_tagset_busy_iter()?
Thanks,
Bart.
