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Date: Wed, 16 Mar 2022 13:46:46 -0700 From: Tony Nguyen <anthony.l.nguyen@...el.com> To: Alexander Duyck <alexander.duyck@...il.com> CC: "kuba@...nel.org" <kuba@...nel.org>, lkp <lkp@...el.com>, "Karlsson, Magnus" <magnus.karlsson@...el.com>, "davem@...emloft.net" <davem@...emloft.net>, "Lobakin, Alexandr" <alexandr.lobakin@...el.com>, "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>, "dan.carpenter@...cle.com" <dan.carpenter@...cle.com>, "pabeni@...hat.com" <pabeni@...hat.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "G, GurucharanX" <gurucharanx.g@...el.com> Subject: Re: [PATCH net 1/3] ice: fix NULL pointer dereference in ice_update_vsi_tx_ring_stats() On 3/16/2022 1:24 PM, Alexander Duyck wrote: > On Wed, Mar 16, 2022 at 12:01 PM Nguyen, Anthony L > <anthony.l.nguyen@...el.com> wrote: >> On Tue, 2022-03-15 at 20:29 -0700, Jakub Kicinski wrote: >>> On Tue, 15 Mar 2022 14:12:23 -0700 Tony Nguyen wrote: >>>> From: Maciej Fijalkowski <maciej.fijalkowski@...el.com> > <snip> > >>>> pointer is valid, but later on ring is accessed to propagate >>>> gathered Tx >>>> stats onto VSI stats. >>>> >>>> Change the existing logic to move to next ring when ring is NULL. >>>> >>>> Fixes: e72bba21355d ("ice: split ice_ring onto Tx/Rx separate >>>> structs") >>>> Reported-by: kernel test robot <lkp@...el.com> >>>> Reported-by: Dan Carpenter <dan.carpenter@...cle.com> >>>> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com> >>>> Acked-by: Alexander Lobakin <alexandr.lobakin@...el.com> >>>> Tested-by: Gurucharan G <gurucharanx.g@...el.com> (A Contingent >>>> worker at Intel) >>>> Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com> >>>> --- >>>> drivers/net/ethernet/intel/ice/ice_main.c | 5 +++-- >>>> 1 file changed, 3 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/net/ethernet/intel/ice/ice_main.c >>>> b/drivers/net/ethernet/intel/ice/ice_main.c >>>> index 493942e910be..d4a7c39fd078 100644 >>>> --- a/drivers/net/ethernet/intel/ice/ice_main.c >>>> +++ b/drivers/net/ethernet/intel/ice/ice_main.c >>>> @@ -5962,8 +5962,9 @@ ice_update_vsi_tx_ring_stats(struct ice_vsi >>>> *vsi, >>>> u64 pkts = 0, bytes = 0; >>>> >>>> ring = READ_ONCE(rings[i]); >>> Not really related to this patch but why is there a read_once() here? >>> Aren't stats read under rtnl_lock? What is this protecting against? >> It looks like it was based on a patch from i40e [1]. From the commit, I >> gather this is the reason: >> >> "Previously the stats were 64 bit but highly racy due to the fact that >> 64 bit transactions are not atomic on 32 bit systems." >> >> Thanks, >> >> Tony >> >> [1] >> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=980e9b1186424fa3eb766d59fc91003d0ed1ed6a >> >> >> (Resending as some non-text formatting snuck in to my reply. Sorry for >> the spam) > Actually the rcu locking and READ_ONCE has to do with the fact that > the driver code for the igb/ixgbe/i40e driver had a bunch of code that > could kick in from the sysfs and/or PCIe paths that would start > tearing things down without necessarily holding the rtnl_lock as it > should have. > > It might make sense to reevaluate the usage of the READ_ONCE and rcu > locking to determine if it is actually needed since much of that is a > hold over from when we were doing this in the watchdog and not while > holding the rtnl_lock in the stats call. Thanks for clarifying Alex. I'll ask the teams to look into this.
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