[PATCH] blk-mq: Avoid that I/O hangs in bt_get()
From: Bart Van Assche
Date: Mon Oct 06 2014 - 08:27:13 EST
Ensure that bt_clear_tag() increments bs->wait_cnt if one or more
threads are waiting for a tag. Remove a superfluous
waitqueue_active() call from blk_mq_tag_wakeup_all(). This patch
avoids that bt_get() hangs as follows if the number of hardware
contexts is below the number of CPU threads:
INFO: task fio:6739 blocked for more than 120 seconds.
Not tainted 3.17.0-rc7+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio D ffff88085fcd2740 0 6739 6688 0x00000000
ffff8807fb96f830 0000000000000086 ffff8808350eb000 ffff8807fb96ffd8
0000000000012740 0000000000012740 ffff88085b885000 ffff8808350eb000
ffff88085fcd2fe0 ffff8807fb96f920 ffff88080061ddc8 ffffe8ffffcc4600
Call Trace:
[<ffffffff8142f52d>] io_schedule+0x9d/0x130
[<ffffffff812016bf>] bt_get+0xef/0x180
[<ffffffff8107f440>] ? prepare_to_wait_event+0x110/0x110
[<ffffffff81201a0f>] blk_mq_get_tag+0x9f/0xd0
[<ffffffff811fdedb>] __blk_mq_alloc_request+0x1b/0x200
[<ffffffff811ff3bc>] blk_mq_map_request+0x15c/0x1b0
[<ffffffff8120079e>] blk_mq_make_request+0x6e/0x270
[<ffffffff8110a99f>] ? mempool_alloc+0x4f/0x130
[<ffffffff811f3af0>] generic_make_request+0xc0/0x110
[<ffffffff811f3bab>] submit_bio+0x6b/0x140
[<ffffffff81110e4b>] ? set_page_dirty_lock+0x2b/0x40
[<ffffffff811eea57>] ? bio_set_pages_dirty+0x47/0x60
[<ffffffff811907d0>] do_blockdev_direct_IO+0x2080/0x3220
[<ffffffff8118bac0>] ? I_BDEV+0x10/0x10
[<ffffffff811919bc>] __blockdev_direct_IO+0x4c/0x50
[<ffffffff8118bac0>] ? I_BDEV+0x10/0x10
[<ffffffff8118c1de>] blkdev_direct_IO+0x4e/0x50
[<ffffffff8118bac0>] ? I_BDEV+0x10/0x10
[<ffffffff81109a13>] generic_file_read_iter+0x513/0x5e0
[<ffffffff8119d8a7>] ? kiocb_free+0x37/0x40
[<ffffffff8118c660>] ? ioctl_by_bdev+0x40/0x40
[<ffffffff8118c697>] blkdev_read_iter+0x37/0x40
[<ffffffff8119e6b4>] aio_run_iocb+0x1e4/0x3c0
[<ffffffff8114dfa6>] ? kmem_cache_alloc+0xd6/0x3d0
[<ffffffff8114e045>] ? kmem_cache_alloc+0x175/0x3d0
[<ffffffff8119f5cc>] do_io_submit+0x11c/0x490
[<ffffffff8119f950>] SyS_io_submit+0x10/0x20
[<ffffffff81432fd2>] system_call_fastpath+0x16/0x1b
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Cc: Robert Elliott <Elliott@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
block/blk-mq-tag.c | 31 +++++++++++++++----------------
1 file changed, 15 insertions(+), 16 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index b5088f0..08d3b1c 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -80,8 +80,7 @@ static void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags)
for (i = 0; i < BT_WAIT_QUEUES; i++) {
struct bt_wait_state *bs = &bt->bs[wake_index];
- if (waitqueue_active(&bs->wait))
- wake_up(&bs->wait);
+ wake_up(&bs->wait);
wake_index = bt_index_inc(wake_index);
}
@@ -346,20 +345,20 @@ static void bt_clear_tag(struct blk_mq_bitmap_tags *bt, unsigned int tag)
*/
clear_bit_unlock(TAG_TO_BIT(bt, tag), &bt->map[index].word);
- bs = bt_wake_ptr(bt);
- if (!bs)
- return;
-
- wait_cnt = atomic_dec_return(&bs->wait_cnt);
- if (wait_cnt == 0) {
-wake:
- atomic_add(bt->wake_cnt, &bs->wait_cnt);
- bt_index_atomic_inc(&bt->wake_index);
- wake_up(&bs->wait);
- } else if (wait_cnt < 0) {
- wait_cnt = atomic_inc_return(&bs->wait_cnt);
- if (!wait_cnt)
- goto wake;
+ for (;;) {
+ bs = bt_wake_ptr(bt);
+ if (!bs)
+ return;
+
+ wait_cnt = atomic_dec_return(&bs->wait_cnt);
+ if (unlikely(wait_cnt < 0))
+ wait_cnt = atomic_inc_return(&bs->wait_cnt);
+ if (wait_cnt == 0) {
+ atomic_add(bt->wake_cnt, &bs->wait_cnt);
+ bt_index_atomic_inc(&bt->wake_index);
+ wake_up(&bs->wait);
+ return;
+ }
}
}
--
1.8.4.5
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/