[PATCH 6.1 002/451] md/raid10: prevent soft lockup while flush writes

Sasha Levin
2024-03-24T23:12:12Z

From: Yu Kuai <yukuai3@huawei.com>

[ Upstream commit 010444623e7f4da6b4a4dd603a7da7469981e293 ]

Currently, there is no limit for raid1/raid10 plugged bio. While flushing
writes, raid1 has cond_resched() while raid10 doesn't, and too many
writes can cause soft lockup.

Follow up soft lockup can be triggered easily with writeback test for
raid10 with ramdisks:

watchdog: BUG: soft lockup - CPU#10 stuck for 27s! [md0_raid10:1293]
Call Trace:
<TASK>
call_rcu+0x16/0x20
put_object+0x41/0x80
__delete_object+0x50/0x90
delete_object_full+0x2b/0x40
kmemleak_free+0x46/0xa0
slab_free_freelist_hook.constprop.0+0xed/0x1a0
kmem_cache_free+0xfd/0x300
mempool_free_slab+0x1f/0x30
mempool_free+0x3a/0x100
bio_free+0x59/0x80
bio_put+0xcf/0x2c0
free_r10bio+0xbf/0xf0
raid_end_bio_io+0x78/0xb0
one_write_done+0x8a/0xa0
raid10_end_write_request+0x1b4/0x430
bio_endio+0x175/0x320
brd_submit_bio+0x3b9/0x9b7 [brd]
__submit_bio+0x69/0xe0
submit_bio_noacct_nocheck+0x1e6/0x5a0
submit_bio_noacct+0x38c/0x7e0
flush_pending_writes+0xf0/0x240
raid10d+0xac/0x1ed0

Fix the problem by adding cond_resched() to raid10 like what raid1 did.

Note that unlimited plugged bio still need to be optimized, for example,
in the case of lots of dirty pages writeback, this will take lots of
memory and io will spend a long time in plug, hence io latency is bad.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230529131106.2123367-2-yukuai1@huaweicloud.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/md/raid10.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 7b318e7e8d459..009f7ffe4e10c 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -920,6 +920,7 @@ static void flush_pending_writes(struct r10conf *conf)

raid1_submit_write(bio);
bio = next;
+ cond_resched();
}
blk_finish_plug(&plug);
} else
@@ -1130,6 +1131,7 @@ static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)

raid1_submit_write(bio);
bio = next;
+ cond_resched();
}
kfree(plug);
}
--
2.43.0