Messages in this thread | | | Subject | Re: [PATCH] scsi: storvsc: Cap scsi_driver.can_queue to fix a hang issue during boot | From | John Garry <> | Date | Wed, 6 Oct 2021 09:17:09 +0100 |
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On 06/10/2021 08:03, Dexuan Cui wrote: > After commit ea2f0f77538c, a 416-CPU VM running on Hyper-V hangs during > boot because scsi_add_host_with_dma() sets shost->cmd_per_lun to a > negative number: > 'max_outstanding_req_per_channel' is 352, > 'max_sub_channels' is (416 - 1) / 4 = 103, so in storvsc_probe(), > scsi_driver.can_queue = 352 * (103 + 1) * (100 - 10) / 100 = 32947, which > is bigger than SHRT_MAX (i.e. 32767).
Out of curiosity, are these values realistic? You're capping can_queue just because of a data size issue, so, if these values are realistic, seems a weak reason.
> > Fix the hang issue by capping scsi_driver.can_queue. > > Add the below Fixed tag though ea2f0f77538c itself is good. > > Fixes: ea2f0f77538c ("scsi: core: Cap scsi_host cmd_per_lun at can_queue") > Cc: stable@vger.kernel.org > Signed-off-by: Dexuan Cui <decui@microsoft.com> > --- > drivers/scsi/storvsc_drv.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c > index ebbbc1299c62..ba374908aec2 100644 > --- a/drivers/scsi/storvsc_drv.c > +++ b/drivers/scsi/storvsc_drv.c > @@ -1976,6 +1976,16 @@ static int storvsc_probe(struct hv_device *device, > (max_sub_channels + 1) * > (100 - ring_avail_percent_lowater) / 100; > > + /* > + * v5.14 (see commit ea2f0f77538c) implicitly requires that > + * scsi_driver.can_queue should not exceed SHRT_MAX, otherwise > + * scsi_add_host_with_dma() sets shost->cmd_per_lun to a negative > + * number (note: the type of the "cmd_per_lun" field is "short"), and > + * the system may hang during early boot. > + */
The different data sizes for cmd_per_lun and can_queue are problematic here.
I'd be more inclined to set cmd_per_lun to the same data size as can_queue. We did discuss this when ea2f0f77538c was upstreamed (actually it was the other way around - setting can_queue to 16b).
Thanks, John
> + if (scsi_driver.can_queue > SHRT_MAX) > + scsi_driver.can_queue = SHRT_MAX; > + > host = scsi_host_alloc(&scsi_driver, > sizeof(struct hv_host_device)); > if (!host) >
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