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Message-ID: <BY3PR18MB4612FC497A8B12889548FF82ABA39@BY3PR18MB4612.namprd18.prod.outlook.com> Date: Wed, 15 Feb 2023 21:20:30 +0000 From: Manish Chopra <manishc@...vell.com> To: Daniil Tatianin <d-tatianin@...dex-team.ru>, Simon Horman <simon.horman@...igine.com> CC: Ariel Elior <aelior@...vell.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Yuval Mintz <Yuval.Mintz@...gic.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: RE: [EXT] Re: [PATCH v0] qed/qed_dev: guard against a possible division by zero > -----Original Message----- > From: Daniil Tatianin <d-tatianin@...dex-team.ru> > Sent: Tuesday, February 14, 2023 12:53 PM > To: Simon Horman <simon.horman@...igine.com> > Cc: Ariel Elior <aelior@...vell.com>; Manish Chopra > <manishc@...vell.com>; David S. Miller <davem@...emloft.net>; Eric > Dumazet <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo > Abeni <pabeni@...hat.com>; Yuval Mintz <Yuval.Mintz@...gic.com>; > netdev@...r.kernel.org; linux-kernel@...r.kernel.org > Subject: [EXT] Re: [PATCH v0] qed/qed_dev: guard against a possible division > by zero > > External Email > > ---------------------------------------------------------------------- > > > On 2/9/23 2:13 PM, Simon Horman wrote: > > On Thu, Feb 09, 2023 at 01:38:13PM +0300, Daniil Tatianin wrote: > >> Previously we would divide total_left_rate by zero if num_vports > >> happened to be 1 because non_requested_count is calculated as > >> num_vports - req_count. Guard against this by explicitly checking for > >> zero when doing the division. > >> > >> Found by Linux Verification Center (linuxtesting.org) with the SVACE > >> static analysis tool. > >> > >> Fixes: bcd197c81f63 ("qed: Add vport WFQ configuration APIs") > >> Signed-off-by: Daniil Tatianin <d-tatianin@...dex-team.ru> > >> --- > >> drivers/net/ethernet/qlogic/qed/qed_dev.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/drivers/net/ethernet/qlogic/qed/qed_dev.c > >> b/drivers/net/ethernet/qlogic/qed/qed_dev.c > >> index d61cd32ec3b6..90927f68c459 100644 > >> --- a/drivers/net/ethernet/qlogic/qed/qed_dev.c > >> +++ b/drivers/net/ethernet/qlogic/qed/qed_dev.c > >> @@ -5123,7 +5123,7 @@ static int qed_init_wfq_param(struct qed_hwfn > >> *p_hwfn, > >> > >> total_left_rate = min_pf_rate - total_req_min_rate; > >> > >> - left_rate_per_vp = total_left_rate / non_requested_count; > >> + left_rate_per_vp = total_left_rate / (non_requested_count ?: 1); > > > > I don't know if num_vports can be 1. > > But if it is then I agree that the above will be a divide by zero. > > > > I do, however, wonder if it would be better to either: > > > > * Treat this case as invalid and return with -EINVAL if num_vports is > > 1; or > I think that's a good idea considering num_vports == 1 is indeed an invalid > value. > I'd like to hear a maintainer's opinion on this. Practically, this flow will only hit with presence of SR-IOV VFs. In that case it's always expected to have num_vports > 1. > > * Skip both the calculation immediately above and the code > > in the if condition below, which is the only place where > > the calculated value is used, if num_vports is 1. > > I don't think the if clause makes much sense if num_vports is > > one.left_rate_per_vp is also used below the if clause, it is assigned > > to > .min_speed in a for loop. Looking at that code division by 1 seems to make > sense to me in this case. > > > >> if (left_rate_per_vp < min_pf_rate / QED_WFQ_UNIT) { > >> DP_VERBOSE(p_hwfn, NETIF_MSG_LINK, > >> "Non WFQ configured vports rate [%d Mbps] is less > than one > >> percent of configured PF min rate[%d Mbps]\n", > >> -- > >> 2.25.1 > >>
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