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Tue, 03 Nov 2026 02:34:42 -0800 (PST) Received: from localhost.localdomain ([2a06:c701:4745:6c00:3cda:8d8e:309a:f6c8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4abea533a1esm223581865e9.1.2026.11.03.02.34.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 02:34:42 -0800 (PST) From: Avi Weiss To: anna-maria@linutronix.de, frederic@kernel.org, tglx@kernel.org Cc: linux-kernel@vger.kernel.org, Avi Weiss Subject: [PATCH] timers: Stop hrtimer queue traversal after seq_file overflow Date: Tue, 3 Nov 2026 12:34:39 +0200 Message-ID: <20261103103438.2154751-2-thnkslprpt@gmail.com> X-Mailer: git-send-email 2.43.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When /proc/timer_list overflows its seq_file buffer, seq_file retries formatting with a larger buffer. print_active_timers() nevertheless continues scanning the remaining hrtimers, restarting its quadratic traversal even though the overflowing attempt will be discarded. Stop traversing at next_one when the seq_file has overflowed. Preserve the SysRq console path, which passes a NULL seq_file pointer. In a (virtual) two-CPU KVM guest with 2,048 timerfds pinned to one CPU, median reader CPU time for a complete /proc/timer_list read fell from 51.1 ms to 14.6 ms. Repeated tests showed no material slowdown for non-overflowing reads (13.7us before versus 13.8 after). Short reads, seek-to-start, and SysRq-Q tests also look fine. Fixes: 289f480af87e ("[PATCH] Add debugging feature /proc/timer_list") Signed-off-by: Avi Weiss --- kernel/time/timer_list.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c index 0406bf4488e9..84275b6cd2c9 100644 --- a/kernel/time/timer_list.c +++ b/kernel/time/timer_list.c @@ -64,6 +64,8 @@ static void print_active_timers(struct seq_file *m, struct hrtimer_clock_base *b unsigned long flags; next_one: + if (m && seq_has_overflowed(m)) + return; i = 0; touch_nmi_watchdog(); -- 2.43.0