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Mon, 10 Feb 2025 22:24:53 -0800 (PST) Received: from localhost.localdomain ([58.37.132.225]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-21f363df2b4sm89016985ad.0.2025.02.10.22.24.51 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 10 Feb 2025 22:24:53 -0800 (PST) From: Yafang Shao To: jpoimboe@kernel.org, jikos@kernel.org, mbenes@suse.cz, pmladek@suse.com, joe.lawrence@redhat.com Cc: live-patching@vger.kernel.org, Yafang Shao Subject: [PATCH 3/3] livepatch: Avoid potential RCU stalls in klp transition Date: Tue, 11 Feb 2025 14:24:37 +0800 Message-Id: <20250211062437.46811-4-laoar.shao@gmail.com> X-Mailer: git-send-email 2.37.1 (Apple Git-137.1) In-Reply-To: <20250211062437.46811-1-laoar.shao@gmail.com> References: <20250211062437.46811-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: live-patching@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit During the livepatch loading process, several RCU warnings were triggered on our production servers, as shown below: [20329161.705294] livepatch: enabling patch 'livepatch_61_release6' [20329161.713184] livepatch: 'livepatch_61_release6': starting patching transition [20329172.998661] rcu_tasks_wait_gp: rcu_tasks grace period 1109713 is 10099 jiffies old. [20329193.049536] rcu_tasks_wait_gp: rcu_tasks grace period 1109717 is 10059 jiffies old. [20329213.131403] rcu_tasks_wait_gp: rcu_tasks grace period 1109725 is 10037 jiffies old. [20329213.934005] livepatch: 'livepatch_61_release6': patching complete The cause of these warnings was that the KLP transition was holding the tasklist_lock (which is part of the RCU read-side critical section) for too long, triggering the warning. To resolve this, we should avoid holding the lock for an extended period. By checking need_resched(), we can ensure the RCU warning no longer appears. Signed-off-by: Yafang Shao --- kernel/livepatch/transition.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c index 04704a19dcfe..3d1f8d3d0f5a 100644 --- a/kernel/livepatch/transition.c +++ b/kernel/livepatch/transition.c @@ -491,9 +491,18 @@ void klp_try_complete_transition(void) complete = false; break; } + + /* Avoid potential RCU stalls */ + if (need_resched()) { + complete = false; + break; + } } read_unlock(&tasklist_lock); + /* The above operation might be expensive. */ + cond_resched(); + /* * Ditto for the idle "swapper" tasks. */ -- 2.43.5