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
