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[2a02:3100:a017:2b01:5fe:203b:7cd2:a640]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fcd12ad97sm84083545e9.13.2026.09.19.07.40.38 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 19 Sep 2026 07:40:38 -0700 (PDT) From: Karl Mehltretter To: Thomas Gleixner , Peter Zijlstra Cc: Karl Mehltretter , Anna-Maria Behnsen , Frederic Weisbecker , Andy Lutomirski , linux-kernel@vger.kernel.org Subject: [PATCH] hrtimer: Use the mask to clear TIF_HRTIMER_REARM from the exit work Date: Sat, 19 Sep 2026 16:40:27 +0200 Message-Id: <20260919144027.70250-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" hrtimer_rearm_deferred_user_irq() removes the rearm bit from the local copy of the TIF work with: *tif_work &=3D ~TIF_HRTIMER_REARM; TIF_HRTIMER_REARM is the bit number (12), not the mask. That clears TIF_NOTIFY_SIGNAL (bit 2) and TIF_MEMDIE (bit 3) from the copy and leaves bit 12 set. So the function never returns true, and the copy handed to exit_to_user_mode_loop() lacks TIF_NOTIFY_SIGNAL. If that was the only work for the loop, the task returns to user space with the task work still pending. hrtimer_interrupt() sets TIF_HRTIMER_REARM every time, so the next tick repeats that. Task work queued with TWA_SIGNAL from a hrtimer callback stays pending until the task does a syscall, takes an interrupt without deferred rearm or has to reschedule. A task which polls the io_uring completion ring in user space sees a timeout completion after 30ms (median) instead of 70us. 2 CPU QEMU guest, HZ=3D1000. Use the mask. Fixes: 15dd3a948855 ("hrtimer: Push reprogramming timers into the interrupt= return path") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Karl Mehltretter --- include/linux/hrtimer_rearm.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/hrtimer_rearm.h b/include/linux/hrtimer_rearm.h index 17a81826bd9a9..12e42721c8e01 100644 --- a/include/linux/hrtimer_rearm.h +++ b/include/linux/hrtimer_rearm.h @@ -45,7 +45,7 @@ hrtimer_rearm_deferred_user_irq(unsigned long *tif_work, = const unsigned long tif clear_thread_flag(TIF_HRTIMER_REARM); __hrtimer_rearm_deferred(); /* Don't go into the loop if HRTIMER_REARM was the only flag */ - *tif_work &=3D ~TIF_HRTIMER_REARM; + *tif_work &=3D ~_TIF_HRTIMER_REARM; return !*tif_work; } return false; base-commit: 40288c9206c17eb66a603262e06a58d300d0f279 --=20 2.53.0