From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:62104 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730149AbgCaQXN (ORCPT ); Tue, 31 Mar 2020 12:23:13 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 02VG3JOq057587 for ; Tue, 31 Mar 2020 12:23:12 -0400 Received: from e06smtp01.uk.ibm.com (e06smtp01.uk.ibm.com [195.75.94.97]) by mx0b-001b2d01.pphosted.com with ESMTP id 30206ye906-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 31 Mar 2020 12:23:11 -0400 Received: from localhost by e06smtp01.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 31 Mar 2020 17:22:57 +0100 Subject: Re: [RFC PATCH v1 27/50] drivers/s390/scsi/zcsp_fc.c: Use prandom_u32_max() for backoff References: <202003281643.02SGhHN7015213@sdf.org> <20200331161321.GB17507@t480-pf1aa2c2> From: Steffen Maier Date: Tue, 31 Mar 2020 18:23:04 +0200 MIME-Version: 1.0 In-Reply-To: <20200331161321.GB17507@t480-pf1aa2c2> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Sender: linux-s390-owner@vger.kernel.org List-ID: To: Benjamin Block , George Spelvin Cc: linux-kernel@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Christian Borntraeger , linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org 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 >> Cc: Heiko Carstens >> Cc: Vasily Gorbik >> Cc: Christian Borntraeger >> 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 > > 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 https://www.ibm.com/privacy/us/en/ IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Matthias Hartmann Geschaeftsfuehrung: Dirk Wittkopp Sitz der Gesellschaft: Boeblingen Registergericht: Amtsgericht Stuttgart, HRB 243294