Messages in this thread |  | | Subject | Re: [RFC PATCH v1 27/50] drivers/s390/scsi/zcsp_fc.c: Use prandom_u32_max() for backoff | From | Steffen Maier <> | Date | Tue, 31 Mar 2020 18:23:04 +0200 |
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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@sdf.org> >> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> >> Cc: Vasily Gorbik <gor@linux.ibm.com> >> Cc: Christian Borntraeger <borntraeger@de.ibm.com> >> Cc: linux-s390@vger.kernel.org >> --- >> 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@linux.ibm.com>
> > 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
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