Re: [PATCH] scsi: storvsc: Cap scsi_driver.can_queue to fix a hang issue during boot
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From: John Garry <hidden>
Date: 2021-10-06 08:14:43
Also in:
linux-scsi, lkml, stable
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.
quoted hunk ↗ jump to hunk
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
quoted hunk ↗ jump to hunk
+ 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)