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[2003:d9:93c9:1300:48e:b295:eb0d:2ef5]) by smtp.googlemail.com with ESMTPSA id w9-v6sm6631957wrk.28.2018.07.17.20.55.12 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 Jul 2018 20:55:12 -0700 (PDT) Subject: Re: [PATCH -next] ipc/sem: prevent queue.status tearing in semop To: Davidlohr Bueso , akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, Davidlohr Bueso References: <20180717052654.676-1-dave@stgolabs.net> From: Manfred Spraul Message-ID: <7909e12b-6dd7-e28a-010c-003545a8e4b5@colorfullife.com> Date: Wed, 18 Jul 2018 05:55:11 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180717052654.676-1-dave@stgolabs.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Davidlohr, On 07/17/2018 07:26 AM, Davidlohr Bueso wrote: > In order for load/store tearing to work, _all_ accesses to > the variable in question need to be done around READ and > WRITE_ONCE() macros. Ensure everyone does so for q->status > variable for semtimedop(). What is the background of the above rule? sma->use_global_lock is sometimes used with smp_load_acquire(), sometimes without. So far, I assumed that this is safe. The same applies for nf_conntrack_locks_all, in nf_conntrack_all_lock() > Signed-off-by: Davidlohr Bueso > --- > ipc/sem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/ipc/sem.c b/ipc/sem.c > index 6cbbf34a44ac..ccab4e51d351 100644 > --- a/ipc/sem.c > +++ b/ipc/sem.c > @@ -2125,7 +2125,7 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops, > } > > do { > - queue.status = -EINTR; > + WRITE_ONCE(queue.status, -EINTR); > queue.sleeper = current; > > __set_current_state(TASK_INTERRUPTIBLE);