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blk-wbt: introduce a new disable state to prevent false positive by rwb_enabled()

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Now that we disable wbt by simply zero out rwb->wb_normal in
wbt_disable_default() when switch elevator to bfq, but it's not safe
because it will become false positive if we change queue depth. If it
become false positive between wbt_wait() and wbt_track() when submit
write request, it will lead to drop rqw->inflight to -1 in wbt_done(),
which will end up trigger IO hung. Fix this issue by introduce a new
state which mean the wbt was disabled.

Fixes: a79050434b ("blk-rq-qos: refactor out common elements of blk-wbt")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://lore.kernel.org/r/20210619093700.920393-2-yi.zhang@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Zhang Yi 2021-06-19 17:36:59 +08:00 committed by Jens Axboe
parent fb926032b3
commit 1d0903d61e
2 changed files with 4 additions and 2 deletions
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5
block/blk-wbt.c
View File

@ -77,7 +77,8 @@ enum {
static inline bool rwb_enabled(struct rq_wb *rwb)
{
return rwb && rwb->wb_normal != 0;
return rwb && rwb->enable_state != WBT_STATE_OFF_DEFAULT &&
rwb->wb_normal != 0;
}
static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
@ -701,7 +702,7 @@ void wbt_disable_default(struct request_queue *q)
rwb = RQWB(rqos);
if (rwb->enable_state == WBT_STATE_ON_DEFAULT) {
blk_stat_deactivate(rwb->cb);
rwb->wb_normal = 0;
rwb->enable_state = WBT_STATE_OFF_DEFAULT;
}
}
EXPORT_SYMBOL_GPL(wbt_disable_default);

1
block/blk-wbt.h
View File

@ -34,6 +34,7 @@ enum {
enum {
WBT_STATE_ON_DEFAULT = 1,
WBT_STATE_ON_MANUAL = 2,
WBT_STATE_OFF_DEFAULT
};
struct rq_wb {