On Fri, 2014-06-06 at 12:18 -0500, Mike Christie wrote: > On 6/5/14, 9:53 PM, KY Srinivasan wrote: > > > > > >> -----Original Message----- > >> From: Mike Christie [mailto:michaelc@xxxxxxxxxxx] > >> Sent: Thursday, June 5, 2014 6:33 PM > >> To: KY Srinivasan > >> Cc: James Bottomley; linux-kernel@xxxxxxxxxxxxxxx; apw@xxxxxxxxxxxxx; > >> devel@xxxxxxxxxxxxxxxxxxxxxx; hch@xxxxxxxxxxxxx; linux- > >> scsi@xxxxxxxxxxxxxxx; ohering@xxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; > >> jasowang@xxxxxxxxxx > >> Subject: Re: [PATCH 1/1] [SCSI] Fix a bug in deriving the FLUSH_TIMEOUT > >> from the basic I/O timeout > >> > >> On 06/04/2014 12:15 PM, KY Srinivasan wrote: > >>> > >>> > >>>> -----Original Message----- > >>>> From: James Bottomley [mailto:jbottomley@xxxxxxxxxxxxx] > >>>> Sent: Wednesday, June 4, 2014 10:02 AM > >>>> To: KY Srinivasan > >>>> Cc: linux-kernel@xxxxxxxxxxxxxxx; apw@xxxxxxxxxxxxx; > >>>> devel@xxxxxxxxxxxxxxxxxxxxxx; hch@xxxxxxxxxxxxx; linux- > >>>> scsi@xxxxxxxxxxxxxxx; ohering@xxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; > >>>> jasowang@xxxxxxxxxx > >>>> Subject: Re: [PATCH 1/1] [SCSI] Fix a bug in deriving the > >>>> FLUSH_TIMEOUT from the basic I/O timeout > >>>> > >>>> On Wed, 2014-06-04 at 09:33 -0700, K. Y. Srinivasan wrote: > >>>>> Commit ID: 7e660100d85af860e7ad763202fff717adcdaacd added code to > >>>>> derive the FLUSH_TIMEOUT from the basic I/O timeout. However, this > >>>>> patch did not use the basic I/O timeout of the device. Fix this bug. > >>>>> > >>>>> Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx> > >>>>> --- > >>>>> drivers/scsi/sd.c | 4 +++- > >>>>> 1 files changed, 3 insertions(+), 1 deletions(-) > >>>>> > >>>>> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index > >>>>> e9689d5..54150b1 100644 > >>>>> --- a/drivers/scsi/sd.c > >>>>> +++ b/drivers/scsi/sd.c > >>>>> @@ -832,7 +832,9 @@ static int sd_setup_write_same_cmnd(struct > >>>>> scsi_device *sdp, struct request *rq) > >>>>> > >>>>> static int scsi_setup_flush_cmnd(struct scsi_device *sdp, struct > >>>>> request *rq) { > >>>>> - rq->timeout *= SD_FLUSH_TIMEOUT_MULTIPLIER; > >>>>> + int timeout = sdp->request_queue->rq_timeout; > >>>>> + > >>>>> + rq->timeout = (timeout * SD_FLUSH_TIMEOUT_MULTIPLIER); > >>>> > >>>> Could you share where you found this to be a problem? It looks like > >>>> a bug in block because all inbound requests being prepared should > >>>> have a timeout set, so block would be the place to fix it. > >>> > >>> Perhaps; what I found was that the value in rq->timeout was 0 coming > >>> into this function and thus multiplying obviously has no effect. > >>> > >> > >> I think you are right. We hit this problem because we are doing: > >> > >> scsi_request_fn -> blk_peek_request -> sd_prep_fn -> > >> scsi_setup_flush_cmnd. > >> > >> At this time request->timeout is zero so the multiplication does nothing. See > >> how sd_setup_write_same_cmnd will set the request->timeout at this time. > >> > >> Then in scsi_request_fn we do: > >> > >> scsi_request_fn -> blk_start_request -> blk_add_timer. > >> > >> At this time it will set the request->timeout if something like req block pc > >> users (like scsi_execute() or block/scsi_ioctl.c) or the write same code > >> mentioned above have not set the timeout. > > > > I don't think this is a recent change. Prior to this commit, we were setting the timeout > > value in this function; it just happened to be a different constant unrelated to the I/O > > timeout. > > > > Yeah, it looks like when 7e660100d85af860e7ad763202fff717adcdaacd was > merged we were supposed to initialize it like in your patch in this thread. > > I guess we could do your patch in this thread, or if we want the block > layer to initialize the timeout before the prep_fn callout is called > then we would need to have the blk-flush.c code to that when it sets up > the request. If we do the latter, do we want the discard and write same > code to initialize the request's timeout before the prep_fn callout is > called too? I looked through the call chain; it seems to be intentional behaviour on the part of block. Just from an mq point of view, it would make better code if we unconditionally initialised rq->timeout early and allowed prep to modify it and then dumped the if(!req->timeout) in blk_add_timer(), but it's a marginal if condition that would compile to a conditional store on sensible architectures, so losing the conditional probably isn't worth worrying about. Cc'd Jens for his opinion with the block patch James --- diff --git a/block/blk-core.c b/block/blk-core.c index a0e3096..cad6b2a 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -111,6 +111,7 @@ void blk_rq_init(struct request_queue *q, struct request *rq) rq->cmd = rq->__cmd; rq->cmd_len = BLK_MAX_CDB; rq->tag = -1; + rq->timeout = q->rq_timeout; rq->start_time = jiffies; set_start_time_ns(rq); rq->part = NULL; diff --git a/block/blk-timeout.c b/block/blk-timeout.c index d96f706..9063ade 100644 --- a/block/blk-timeout.c +++ b/block/blk-timeout.c @@ -180,13 +180,6 @@ void __blk_add_timer(struct request *req, struct list_head *timeout_list) BUG_ON(!list_empty(&req->timeout_list)); - /* - * Some LLDs, like scsi, peek at the timeout to prevent a - * command from being retried forever. - */ - if (!req->timeout) - req->timeout = q->rq_timeout; - req->deadline = jiffies + req->timeout; if (timeout_list) list_add_tail(&req->timeout_list, timeout_list); -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
