| Message ID | 1618848384-204144-1-git-send-email-john.garry@huawei.com |
|---|---|
| State | New |
| Headers | show |
| Series | scsi: core: Cap initial sdev queue depth at shost.can_queue | expand |
On Tue, Apr 20, 2021 at 12:06:24AM +0800, John Garry wrote: > Function sdev_store_queue_depth() enforces that the sdev queue depth cannot > exceed shost.can_queue. > > However, the LLDD may still set cmd_per_lun > can_queue, which leads to an > initial sdev queue depth greater than can_queue. > > Stop this happened by capping initial sdev queue depth at can_queue. > > Signed-off-by: John Garry <john.garry@huawei.com> > --- > Topic originally discussed at: > https://lore.kernel.org/linux-scsi/85dec8eb-8eab-c7d6-b0fb-5622747c5499@interlog.com/T/#m5663d0cac657d843b93d0c9a2374f98fc04384b9 > > Last idea there was to error/warn in scsi_add_host() for cmd_per_lun > No, that isn't my suggestion. > can_queue. However, such a shost driver could still configure the sdev > queue depth to be sound value at .slave_configure callback, so now thinking > the orig patch better. As I mentioned last time, why can't we fix ->cmd_per_lun in scsi_add_host() using .can_queue? -- Ming
On 20/04/2021 01:02, Ming Lei wrote: > On Tue, Apr 20, 2021 at 12:06:24AM +0800, John Garry wrote: >> Function sdev_store_queue_depth() enforces that the sdev queue depth cannot >> exceed shost.can_queue. >> >> However, the LLDD may still set cmd_per_lun > can_queue, which leads to an >> initial sdev queue depth greater than can_queue. >> >> Stop this happened by capping initial sdev queue depth at can_queue. >> >> Signed-off-by: John Garry <john.garry@huawei.com> >> --- >> Topic originally discussed at: >> https://lore.kernel.org/linux-scsi/85dec8eb-8eab-c7d6-b0fb-5622747c5499@interlog.com/T/#m5663d0cac657d843b93d0c9a2374f98fc04384b9 >> >> Last idea there was to error/warn in scsi_add_host() for cmd_per_lun > > Hi Ming, > No, that isn't my suggestion. Right, it was what I mentioned. > >> can_queue. However, such a shost driver could still configure the sdev >> queue depth to be sound value at .slave_configure callback, so now thinking >> the orig patch better. > > As I mentioned last time, why can't we fix ->cmd_per_lun in > scsi_add_host() using .can_queue? > I would rather not change the values which are provided from the driver. I would rather take the original values and try to use them in a sane way. I have not seen other places where driver shost config values are modified by the core code. Thanks, John
On Tue, Apr 20, 2021 at 09:14:12AM +0100, John Garry wrote: > On 20/04/2021 01:02, Ming Lei wrote: > > On Tue, Apr 20, 2021 at 12:06:24AM +0800, John Garry wrote: > > > Function sdev_store_queue_depth() enforces that the sdev queue depth cannot > > > exceed shost.can_queue. > > > > > > However, the LLDD may still set cmd_per_lun > can_queue, which leads to an > > > initial sdev queue depth greater than can_queue. > > > > > > Stop this happened by capping initial sdev queue depth at can_queue. > > > > > > Signed-off-by: John Garry <john.garry@huawei.com> > > > --- > > > Topic originally discussed at: > > > https://lore.kernel.org/linux-scsi/85dec8eb-8eab-c7d6-b0fb-5622747c5499@interlog.com/T/#m5663d0cac657d843b93d0c9a2374f98fc04384b9 > > > > > > Last idea there was to error/warn in scsi_add_host() for cmd_per_lun > > > > > Hi Ming, > > > No, that isn't my suggestion. > > Right, it was what I mentioned. > > > > > > can_queue. However, such a shost driver could still configure the sdev > > > queue depth to be sound value at .slave_configure callback, so now thinking > > > the orig patch better. > > > > As I mentioned last time, why can't we fix ->cmd_per_lun in > > scsi_add_host() using .can_queue? > > > > I would rather not change the values which are provided from the driver. I > would rather take the original values and try to use them in a sane way. > > I have not seen other places where driver shost config values are modified > by the core code. Wrt. .cmd_per_lun, I think it is safe to modify it into one correct depth because almost all drivers are just producer of .cmd_per_lun. And except for debug purpose, there are only three consumers of .cmd_per_lun in scsi, and all are for scsi_change_queue_depth(): process_message() scsi_alloc_sdev() virtscsi_change_queue_depth() Thanks, Ming
On 22/04/2021 02:38, Ming Lei wrote: >> I would rather not change the values which are provided from the driver. I >> would rather take the original values and try to use them in a sane way. >> >> I have not seen other places where driver shost config values are modified >> by the core code. Hi Ming, > Wrt. .cmd_per_lun, I think it is safe to modify it into one correct > depth because almost all drivers are just producer of .cmd_per_lun. And > except for debug purpose, there are only three consumers of .cmd_per_lun > in scsi, and all are for scsi_change_queue_depth(): > > process_message() > scsi_alloc_sdev() > virtscsi_change_queue_depth() sg_ioctl_common() also looks to read it, but I can't imagine we could break that interface with either suggested change. So I still prefer not to modify shost.cmd_per_lun, but if you feel strongly enough then I can look to make that change. Thanks, John
On Thu, Apr 22, 2021 at 05:35:42PM +0100, John Garry wrote: > On 22/04/2021 02:38, Ming Lei wrote: > > > I would rather not change the values which are provided from the driver. I > > > would rather take the original values and try to use them in a sane way. > > > > > > I have not seen other places where driver shost config values are modified > > > by the core code. > > Hi Ming, > > > Wrt. .cmd_per_lun, I think it is safe to modify it into one correct > > depth because almost all drivers are just producer of .cmd_per_lun. And > > except for debug purpose, there are only three consumers of .cmd_per_lun > > in scsi, and all are for scsi_change_queue_depth(): > > > > process_message() > > scsi_alloc_sdev() > > virtscsi_change_queue_depth() > > sg_ioctl_common() also looks to read it, but I can't imagine we could break > that interface with either suggested change. Then one bad .cmd_per_lun can be passed to userspace, as your patch doesn't cover this case. > > So I still prefer not to modify shost.cmd_per_lun, but if you feel strongly > enough then I can look to make that change. I still suggest to make .cmd_per_lun correct since the beginning, otherwise you may have to cover anywhere .cmd_per_lun is used. Thanks, Ming
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c index 9f1b7f3c650a..8de2f830bcdc 100644 --- a/drivers/scsi/scsi_scan.c +++ b/drivers/scsi/scsi_scan.c @@ -277,7 +277,11 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget, WARN_ON_ONCE(!blk_get_queue(sdev->request_queue)); sdev->request_queue->queuedata = sdev; - depth = sdev->host->cmd_per_lun ?: 1; + if (sdev->host->cmd_per_lun) + depth = min_t(unsigned int, sdev->host->cmd_per_lun, + sdev->host->can_queue); + else + depth = 1; /* * Use .can_queue as budget map's depth because we have to
Function sdev_store_queue_depth() enforces that the sdev queue depth cannot exceed shost.can_queue. However, the LLDD may still set cmd_per_lun > can_queue, which leads to an initial sdev queue depth greater than can_queue. Stop this happened by capping initial sdev queue depth at can_queue. Signed-off-by: John Garry <john.garry@huawei.com> --- Topic originally discussed at: https://lore.kernel.org/linux-scsi/85dec8eb-8eab-c7d6-b0fb-5622747c5499@interlog.com/T/#m5663d0cac657d843b93d0c9a2374f98fc04384b9 Last idea there was to error/warn in scsi_add_host() for cmd_per_lun > can_queue. However, such a shost driver could still configure the sdev queue depth to be sound value at .slave_configure callback, so now thinking the orig patch better. -- 2.26.2