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[24.6.151.244]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-210bc013477sm69811895ad.175.2024.10.29.12.34.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Oct 2024 12:34:12 -0700 (PDT) Date: Tue, 29 Oct 2024 12:34:10 -0700 From: Joe Damato To: Eric Dumazet Cc: "David S . Miller" , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, eric.dumazet@gmail.com Subject: Re: [PATCH net-next] dql: annotate data-races around dql->last_obj_cnt Message-ID: Mail-Followup-To: Joe Damato , Eric Dumazet , "David S . Miller" , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, eric.dumazet@gmail.com References: <20241029191425.2519085-1-edumazet@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241029191425.2519085-1-edumazet@google.com> On Tue, Oct 29, 2024 at 07:14:25PM +0000, Eric Dumazet wrote: > dql->last_obj_cnt is read/written from different contexts, > without any lock synchronization. > > Use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing. > > Signed-off-by: Eric Dumazet > --- > include/linux/dynamic_queue_limits.h | 2 +- > lib/dynamic_queue_limits.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/linux/dynamic_queue_limits.h b/include/linux/dynamic_queue_limits.h > index 281298e77a1579cba1f92a3b3f03b8be089fd38f..808b1a5102e7c0bbbcd9676b0dacadad2f0ee49a 100644 > --- a/include/linux/dynamic_queue_limits.h > +++ b/include/linux/dynamic_queue_limits.h > @@ -127,7 +127,7 @@ static inline void dql_queued(struct dql *dql, unsigned int count) > if (WARN_ON_ONCE(count > DQL_MAX_OBJECT)) > return; > > - dql->last_obj_cnt = count; > + WRITE_ONCE(dql->last_obj_cnt, count); > > /* We want to force a write first, so that cpu do not attempt > * to get cache line containing last_obj_cnt, num_queued, adj_limit > diff --git a/lib/dynamic_queue_limits.c b/lib/dynamic_queue_limits.c > index e49deddd3de9fe9e98d6712559cf48d12a0a2537..c1b7638a594ac43f947e00decabbd3468dcb53de 100644 > --- a/lib/dynamic_queue_limits.c > +++ b/lib/dynamic_queue_limits.c > @@ -179,7 +179,7 @@ void dql_completed(struct dql *dql, unsigned int count) > > dql->adj_limit = limit + completed; > dql->prev_ovlimit = ovlimit; > - dql->prev_last_obj_cnt = dql->last_obj_cnt; > + dql->prev_last_obj_cnt = READ_ONCE(dql->last_obj_cnt); > dql->num_completed = completed; > dql->prev_num_queued = num_queued; > This looks fine to me. I noted that dql_reset writes last_obj_cnt, but AFAIU that write is not a problem (from the 1 driver I looked at). Reviewed-by: Joe Damato