Re: [PATCH 14/16] block: switch polling to be bio based
flat view
From: Ming Lei <hidden>
Date: 2021-10-13 10:00:21
Also in:
linux-fsdevel, linux-nvme
On Tue, Oct 12, 2021 at 01:12:24PM +0200, Christoph Hellwig wrote:
Replace the blk_poll interface that requires the caller to keep a queue and cookie from the submissions with polling based on the bio. Polling for the bio itself leads to a few advantages: - the cookie construction can made entirely private in blk-mq.c - the caller does not need to remember the request_queue and cookie separately and thus sidesteps their lifetime issues - keeping the device and the cookie inside the bio allows to trivially support polling BIOs remapping by stacking drivers - a lot of code to propagate the cookie back up the submission path can be removed entirely. Signed-off-by: Christoph Hellwig <hch@lst.de> Tested-by: Mark Wunderlich <redacted> ---
...
quoted hunk ↗ jump to hunk
+/** + * bio_poll - poll for BIO completions + * @bio: bio to poll for + * @flags: BLK_POLL_* flags that control the behavior + * + * Poll for completions on queue associated with the bio. Returns number of + * completed entries found. + * + * Note: the caller must either be the context that submitted @bio, or + * be in a RCU critical section to prevent freeing of @bio. + */ +int bio_poll(struct bio *bio, unsigned int flags) +{ + struct request_queue *q = bio->bi_bdev->bd_disk->queue; + blk_qc_t cookie = READ_ONCE(bio->bi_cookie); + int ret; + + if (cookie == BLK_QC_T_NONE || + !test_bit(QUEUE_FLAG_POLL, &q->queue_flags)) + return 0; + + if (current->plug) + blk_flush_plug_list(current->plug, false); + + if (blk_queue_enter(q, BLK_MQ_REQ_NOWAIT)) + return 0;
Now bdev, gendisk and request_queue are freed after RCU grace period, so this
way is safe since 340e84573878 ("block: delay freeing the gendisk").
Thanks,
Ming