Messages in this thread | | | Subject | Re: [RFC PATCH v2 2/2] blk-mq: Lockout tagset iter when freeing rqs | From | John Garry <> | Date | Tue, 22 Dec 2020 11:22:19 +0000 |
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Resend without ppvk@codeaurora.org, which bounces for me
On 22/12/2020 02:13, Bart Van Assche wrote: > On 12/21/20 10:47 AM, John Garry wrote: >> Yes, I agree, and I'm not sure what I wrote to give that impression. >> >> About "root partition", above, I'm just saying that / is mounted on a >> sda partition: >> >> root@ubuntu:/home/john# mount | grep sda >> /dev/sda2 on / type ext4 (rw,relatime,errors=remount-ro,stripe=32) >> /dev/sda1 on /boot/efi type vfat >> (rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro) > Hi John, >
Hi Bart, Ming,
> Thanks for the clarification. I want to take back my suggestion about > adding rcu_read_lock() / rcu_read_unlock() in blk_mq_tagset_busy_iter() > since it is not allowed to sleep inside an RCU read-side critical > section, since blk_mq_tagset_busy_iter() is used in request timeout > handling and since there may be blk_mq_ops.timeout implementations that > sleep.
Yes, that's why I was going with atomic, rather than some synchronization primitive which may sleep.
> > Ming's suggestion to serialize blk_mq_tagset_busy_iter() and > blk_mq_free_rqs() looks interesting to me. >
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?
Thanks, John
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