[PATCH 5.12 172/292] block: fix the problem of io_ticks becoming smaller

From: Greg Kroah-Hartman
Date: Mon Jul 19 2021 - 14:09:50 EST

From: Chunguang Xu <brookxu@xxxxxxxxxxx>

[ Upstream commit d80c228d44640f0b47b57a2ca4afa26ef87e16b0 ]

On the IO submission path, blk_account_io_start() may interrupt
the system interruption. When the interruption returns, the value
of part->stamp may have been updated by other cores, so the time
value collected before the interruption may be less than part->
stamp. So when this happens, we should do nothing to make io_ticks
more accurate? For kernels less than 5.0, this may cause io_ticks
to become smaller, which in turn may cause abnormal ioutil values.

Signed-off-by: Chunguang Xu <brookxu@xxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Link: https://lore.kernel.org/r/1625521646-1069-1-git-send-email-brookxu.cn@xxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
block/blk-core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index fc60ff208497..e34dfa13b7bc 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1255,7 +1255,7 @@ static void update_io_ticks(struct block_device *part, unsigned long now,
unsigned long stamp;
stamp = READ_ONCE(part->bd_stamp);
- if (unlikely(stamp != now)) {
+ if (unlikely(time_after(now, stamp))) {
if (likely(cmpxchg(&part->bd_stamp, stamp, now) == stamp))
__part_stat_add(part, io_ticks, end ? now - stamp : 1);