| Message ID | 20210222065452.21897-1-jefflexu@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: fix potential IO hang when turning off io_poll | expand |
On 2/22/21 2:54 PM, Jeffle Xu wrote: > QUEUE_FLAG_POLL flag will be cleared when turning off 'io_poll', while > at that moment there may be IOs stuck in hw queue uncompleted. The > following polling routine won't help reap these IOs, since blk_poll() > will return immediately because of cleared QUEUE_FLAG_POLL flag. Thus > these IOs will hang until they finnaly time out. The hang out can be > observed by 'fio --engine=io_uring iodepth=1', while turning off > 'io_poll' at the same time. > > To fix this, freeze and flush the request queue first when turning off > 'io_poll'. > > Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> > --- > block/blk-sysfs.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > index b513f1683af0..10d74741c002 100644 > --- a/block/blk-sysfs.c > +++ b/block/blk-sysfs.c > @@ -430,8 +430,11 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page, > > if (poll_on) > blk_queue_flag_set(QUEUE_FLAG_POLL, q); > - else > + else { > + blk_mq_freeze_queue(q); > blk_queue_flag_clear(QUEUE_FLAG_POLL, q); > + blk_mq_unfreeze_queue(q); > + } > > return ret; > } > Better to place brace to 'if' as well. Thanks, Joseph
On 2/22/21 3:12 PM, Joseph Qi wrote: > > > On 2/22/21 2:54 PM, Jeffle Xu wrote: >> QUEUE_FLAG_POLL flag will be cleared when turning off 'io_poll', while >> at that moment there may be IOs stuck in hw queue uncompleted. The >> following polling routine won't help reap these IOs, since blk_poll() >> will return immediately because of cleared QUEUE_FLAG_POLL flag. Thus >> these IOs will hang until they finnaly time out. The hang out can be >> observed by 'fio --engine=io_uring iodepth=1', while turning off >> 'io_poll' at the same time. >> >> To fix this, freeze and flush the request queue first when turning off >> 'io_poll'. >> >> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> >> --- >> block/blk-sysfs.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c >> index b513f1683af0..10d74741c002 100644 >> --- a/block/blk-sysfs.c >> +++ b/block/blk-sysfs.c >> @@ -430,8 +430,11 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page, >> >> if (poll_on) >> blk_queue_flag_set(QUEUE_FLAG_POLL, q); >> - else >> + else { >> + blk_mq_freeze_queue(q); >> blk_queue_flag_clear(QUEUE_FLAG_POLL, q); >> + blk_mq_unfreeze_queue(q); >> + } >> >> return ret; >> } >> > > Better to place brace to 'if' as well. Got it, thanks.
On 2/21/21 11:54 PM, Jeffle Xu wrote: > QUEUE_FLAG_POLL flag will be cleared when turning off 'io_poll', while > at that moment there may be IOs stuck in hw queue uncompleted. The > following polling routine won't help reap these IOs, since blk_poll() > will return immediately because of cleared QUEUE_FLAG_POLL flag. Thus > these IOs will hang until they finnaly time out. The hang out can be > observed by 'fio --engine=io_uring iodepth=1', while turning off > 'io_poll' at the same time. > > To fix this, freeze and flush the request queue first when turning off > 'io_poll'. Applied, thanks. Fixed up the braces.
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index b513f1683af0..10d74741c002 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -430,8 +430,11 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page, if (poll_on) blk_queue_flag_set(QUEUE_FLAG_POLL, q); - else + else { + blk_mq_freeze_queue(q); blk_queue_flag_clear(QUEUE_FLAG_POLL, q); + blk_mq_unfreeze_queue(q); + } return ret; }
QUEUE_FLAG_POLL flag will be cleared when turning off 'io_poll', while at that moment there may be IOs stuck in hw queue uncompleted. The following polling routine won't help reap these IOs, since blk_poll() will return immediately because of cleared QUEUE_FLAG_POLL flag. Thus these IOs will hang until they finnaly time out. The hang out can be observed by 'fio --engine=io_uring iodepth=1', while turning off 'io_poll' at the same time. To fix this, freeze and flush the request queue first when turning off 'io_poll'. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> --- block/blk-sysfs.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)