Message ID | 20240507093530.3043-29-urezki@gmail.com (mailing list archive) |
---|---|
State | Mainlined |
Commit | fc2897d2abe5a307e3b28943bcb4c1401432ea26 |
Headers | show
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[185.121.47.193]) by smtp.gmail.com with ESMTPSA id t18-20020a2e9d12000000b002e29c50c4dcsm1335473lji.27.2024.05.07.02.35.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 May 2024 02:35:59 -0700 (PDT) From: "Uladzislau Rezki (Sony)" <urezki@gmail.com> To: "Paul E . McKenney" <paulmck@kernel.org> Cc: RCU <rcu@vger.kernel.org>, Neeraj upadhyay <Neeraj.Upadhyay@amd.com>, Boqun Feng <boqun.feng@gmail.com>, Hillf Danton <hdanton@sina.com>, Joel Fernandes <joel@joelfernandes.org>, LKML <linux-kernel@vger.kernel.org>, Uladzislau Rezki <urezki@gmail.com>, Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>, Frederic Weisbecker <frederic@kernel.org>, Marco Elver <elver@google.com> Subject: [PATCH 28/48] rcu: Inform KCSAN of one-byte cmpxchg() in rcu_trc_cmpxchg_need_qs() Date: Tue, 7 May 2024 11:35:10 +0200 Message-Id: <20240507093530.3043-29-urezki@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240507093530.3043-1-urezki@gmail.com> References: <20240507093530.3043-1-urezki@gmail.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: <rcu.vger.kernel.org> List-Subscribe: <mailto:rcu+subscribe@vger.kernel.org> List-Unsubscribe: <mailto:rcu+unsubscribe@vger.kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit |
Series |
RCU changes for v6.10
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expand
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diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 147b5945d67a..327fbfc999c8 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1457,6 +1457,7 @@ static void rcu_st_need_qs(struct task_struct *t, u8 v) /* * Do a cmpxchg() on ->trc_reader_special.b.need_qs, allowing for * the four-byte operand-size restriction of some platforms. + * * Returns the old value, which is often ignored. */ u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new) @@ -1468,7 +1469,14 @@ u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new) if (trs_old.b.need_qs != old) return trs_old.b.need_qs; trs_new.b.need_qs = new; - ret.s = cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s); + + // Although cmpxchg() appears to KCSAN to update all four bytes, + // only the .b.need_qs byte actually changes. + instrument_atomic_read_write(&t->trc_reader_special.b.need_qs, + sizeof(t->trc_reader_special.b.need_qs)); + // Avoid false-positive KCSAN failures. + ret.s = data_race(cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s)); + return ret.b.need_qs; } EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs);