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McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, Frederic Weisbecker , "Paul E . McKenney" Subject: [PATCH v3 rcu 10/11] srcu: Explain the reason behind the read side critical section on GP start Date: Wed, 19 Oct 2022 15:58:45 -0700 Message-Id: <20221019225846.2501109-10-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221019225838.GA2500612@paulmck-ThinkPad-P17-Gen-1> References: <20221019225838.GA2500612@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 X-Spam-Status: No, score=-7.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1747158814934961199?= X-GMAIL-MSGID: =?utf-8?q?1747158814934961199?= From: Frederic Weisbecker Tell about the need to protect against concurrent updaters who may overflow the GP counter behind the current update. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 18bb696cff8ca..272830a87e566 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1158,6 +1158,11 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, int ss_state; check_init_srcu_struct(ssp); + /* + * While starting a new grace period, make sure we are in an + * SRCU read-side critical section so that the grace-period + * sequence number cannot wrap around in the meantime. + */ idx = __srcu_read_lock_nmisafe(ssp, false); ss_state = smp_load_acquire(&ssp->srcu_size_state); if (ss_state < SRCU_SIZE_WAIT_CALL)