On Tue, Jul 16, 2019 at 10:53:00AM +0800, John Garry wrote:
> 在 12/07/2019 10:47, Ming Lei 写道:
> > We will stop hw queue and wait for completion of in-flight requests
> > when one hctx is becoming dead in the following patch. This way may
> > cause dead-lock for some stacking blk-mq drivers, such as dm-rq and
> > loop.
> >
> > Add blk-mq flag of BLK_MQ_F_NO_MANAGED_IRQ and mark it for dm-rq and
> > loop, so we needn't to wait for completion of in-flight requests of
> > dm-rq & loop, then the potential dead-lock can be avoided.
>
> Wouldn't it make more sense to have the flag name be like
> BLK_MQ_F_DONT_DRAIN_STOPPED_HCTX?
>
> I did not think that blk-mq is specifically concerned with managed
> interrupts, but only their indirect effect.
I am fine with either one, however it is easier for drivers to
recognize if this flag should be set, given BLK_MQ_F_NO_MANAGED_IRQ
is self-explained.
Also on the other side, this patchset serves a generic blk-mq fix
for managed IRQ issue, so it is reasonable for all drivers which
don't use managed IRQ to set the flag.
>
> >
> > Cc: Bart Van Assche <bvanassche@xxxxxxx>
> > Cc: Hannes Reinecke <hare@xxxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Keith Busch <keith.busch@xxxxxxxxx>
> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > ---
> > block/blk-mq-debugfs.c | 1 +
> > drivers/block/loop.c | 2 +-
> > drivers/md/dm-rq.c | 2 +-
> > include/linux/blk-mq.h | 1 +
> > 4 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
> > index af40a02c46ee..24fff8c90942 100644
> > --- a/block/blk-mq-debugfs.c
> > +++ b/block/blk-mq-debugfs.c
> > @@ -240,6 +240,7 @@ static const char *const hctx_flag_name[] = {
> > HCTX_FLAG_NAME(TAG_SHARED),
> > HCTX_FLAG_NAME(BLOCKING),
> > HCTX_FLAG_NAME(NO_SCHED),
> > + HCTX_FLAG_NAME(NO_MANAGED_IRQ),
> > };
> > #undef HCTX_FLAG_NAME
> > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > index 44c9985f352a..199d76e8bf46 100644
> > --- a/drivers/block/loop.c
> > +++ b/drivers/block/loop.c
> > @@ -1986,7 +1986,7 @@ static int loop_add(struct loop_device **l, int i)
> > lo->tag_set.queue_depth = 128;
> > lo->tag_set.numa_node = NUMA_NO_NODE;
> > lo->tag_set.cmd_size = sizeof(struct loop_cmd);
> > - lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
> > + lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_NO_MANAGED_IRQ;
>
> nit: at this point in the series you're setting a flag which is never
> checked.
Yeah, I see, and this way is a bit easier for review purpose.
thanks,
Ming
