On 3/31/20 6:13 PM, Benjamin Block wrote:
On Fri, Nov 29, 2019 at 03:39:41PM -0500, George Spelvin wrote:
We don't need crypto-grade random numbers for randomized backoffs.
(We could skip the if() if we wanted to rely on the undocumented fact
that prandom_u32_max(0) always returns 0. That would be a net time
saving it port_scan_backoff == 0 is rare; if it's common, the if()
is false often enough to pay for itself. Not sure which applies here.)
Signed-off-by: George Spelvin <lkml@xxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: linux-s390@xxxxxxxxxxxxxxx
---
drivers/s390/scsi/zfcp_fc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Hello George,
it would be nice, if you could address the mails to the
driver-maintainers (`scripts/get_maintainer.pl drivers/s390/scsi/zfcp_fc.c`
will tell you that this is me and Steffen); I'd certainly have noticed
it earlier then :-).
diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
index b018b61bd168e..d24cafe02708f 100644
--- a/drivers/s390/scsi/zfcp_fc.c
+++ b/drivers/s390/scsi/zfcp_fc.c
@@ -48,7 +48,7 @@ unsigned int zfcp_fc_port_scan_backoff(void)
{
if (!port_scan_backoff)
return 0;
- return get_random_int() % port_scan_backoff;
+ return prandom_u32_max(port_scan_backoff);
Reviewed-by: Steffen Maier <maier@xxxxxxxxxxxxx>
I think the change is fine. You are right, we don't need a crypto nonce
here.
I think I'd let the zero-check stand as is, because the internal
behaviour of prandom_u32_max() is, as you say, undocumented. This is not
a performance critical code-path for us anyway.
yes, let's keep the extra check as it's intentional and documented user
interface for zfcp, so better be explicit
}
static void zfcp_fc_port_scan_time(struct zfcp_adapter *adapter)
--
2.26.0
Steffen, do you have any objections? Otherwise I can queue this up -
minus the somewhat mangled subject - for when we send something next time.
--
Mit freundlichen Gruessen / Kind regards
Steffen Maier
Linux on IBM Z Development
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