From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=193.142.43.55 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794233191; b=omtRiPVTTUqyfj/rQkW1+bguQote7IHAOOxP4WScn3Ip2Jbk9Y6fIdIKW6EFjDgjhRic QJf91UqCjtQ0P2z7Rt76LYENfReUM3OVQ0m5CpHKYKdm0s7HIrZX2V5pUC/4jiC2Gzr9X O9s7zTSqFhrjj5YB+pWXyRUx35Bt/TkQc1WiwF3uxxoOODM5uHay/6L3jfgmuq+Fo8xV1 ARVzo0WSxu3NRI+4gjyRTt5urOIFbxW5QgrtK7+vUJknEwaKy/8HAmHVJ4dQH4He83Elm uL+cnIxn9AtwARNRgok7YiWuc+qzgHqpUR04qPaAgpgKWWbhEeDpacmnZjtCJmgVThA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794233191; h=DMARC-Filter:From:DKIM-Signature:DKIM-Signature:To:Cc:Subject: In-Reply-To:References:Date:Message-ID:MIME-Version:Content-Type; bh=0BfdVOGjcuEi8cBY7N3KA/lKr6DLGKrG/Pkl4v81otU=; b=uc3a/s+Xjk6V3NimUsPWP8bOv35Xn96EpRmPFwPRbXciybJ3B5BtYctUQ2/D0hToKNsd ovYoYhKmP6GiOb8vwn5iSlHnFHkC8dVRxrg1w9XJ6ViHNgH1Nx2UHOtVkPNp/x9M0cX+7 aRcHPM6of437dYXop+fNHwaCIBpiE4V9ulE4qHEJ4I637BOKvoHAScwotMsw3d7zKY1PZ n9pWur3USI3eBpSvDqRam05EsJgs/BvHx7YpfHQBoJ1lLOzzEmrvsk1qmSrJwQ2R02DA/ 1busoOhm1f5p99w1qPiRhVpxqcX6Shr9vhd8yuEwpZEPEbpW4kkUzjUNK8AJGrmJY4Q== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=rsa-sha256 header.s=2020 header.b=TRbIbGOX; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=ed25519-sha256 header.s=2020e header.b=fpUkvC7T; arc=none smtp.remote-ip=193.142.43.55 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8BFFE606A31C for ; Mon, 9 Nov 2026 14:06:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 8BFFE606A31C Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.a=rsa-sha256 header.s=2020 header.b=TRbIbGOX; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=ed25519-sha256 header.s=2020e header.b=fpUkvC7T From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1794233187; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=0BfdVOGjcuEi8cBY7N3KA/lKr6DLGKrG/Pkl4v81otU=; b=TRbIbGOXxzA7wAQ3xKKHeRa+zfiMkEXTOL0ZpbW23pZS1V86n/+EFDF/XPvNZYos5dKNkQ bapDeWlZObkQwko2CFx1jdBmrHX4QvHT+Ubm8QGNLlE8EFrWw0lHZ6rZ3y+LzoBFOLuV1Z jvV+k/exoxQ8VLPenfWIIguakZ83FoAY6i/vWRYPA7twEFmes9Qi+XCrxUXzbzX1RvXg7s 1tU7oNmmPtn/B9N6fqTTP0YlNFs5avKmczlfSZ7bP4U7EOfDdM9pB9Qfznm59q8Eysgw7E Tzaddj+eUfMhqtMH0JW76zxH4rv8GirN+U9o3tqFLYqBzY9T01e8JLBgwtX97A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1794233187; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=0BfdVOGjcuEi8cBY7N3KA/lKr6DLGKrG/Pkl4v81otU=; b=fpUkvC7T1ftO+rFh/DyBsoPiVDSeVvwCgkJsrfemAARt93Ci9GOGW5zAmJPU4D8xJmjr/3 a0IhtSK15cN9NOBw== To: Breno Leitao , Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , Waiman Long , Petr Mladek Cc: Marco Elver , Dmitry Vyukov , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, kernel-team@meta.com, Breno Leitao Subject: Re: [PATCH v3] lockdep: Move the emergency section out of print_irqtrace_events() In-Reply-To: <20261109-kcsan-irqtrace-emergency-v3-1-6d62e3406b8d@debian.org> References: <20261109-kcsan-irqtrace-emergency-v3-1-6d62e3406b8d@debian.org> Date: Mon, 09 Nov 2026 15:12:26 +0106 Message-ID: <87qzgucd5p.fsf@jogness.linutronix.de> 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-Type: text/plain On 2026-11-09, Breno Leitao wrote: > Commit 59cd94ef8009 ("lockdep: Mark emergency sections in lockdep > splats") made print_irqtrace_events() enter an nbcon emergency section > by itself. That was meant for lockdep splats, but the function is also > used outside lockdep (by verbose KCSAN reports, the soft and hard > lockup detectors, etc). > > For KCSAN, as print_report() runs with the raw report_lock held and > interrupts disabled, so every verbose report writes out the whole > console backlog under report_lock. Other CPUs that detect a race in the > meantime spin on report_lock with interrupts disabled, as the lock is > taken before rate_limit_report() gets a chance to drop the report. > > That causes this type of problems (as seen in Meta's fleet): > > BUG: KCSAN: data-race in mlx5e_poll_tx_cq+0x5d8/0x998 > ... > irq event stamp: 28975074 > smp: csd: Detected non-responsive CSD lock (#2) on CPU#35, waiting 5000000052 ns for CPU#26 ipi_mb+0x0/0x18(0x0). > smp: csd: Detected non-responsive CSD lock (#3) on CPU#65, waiting 5000000020 ns for CPU#00 do_nothing+0x0/0x18(0x0). > watchdog: CPU71: Watchdog detected hard LOCKUP on cpu 0 > Kernel panic - not syncing: Hard LOCKUP > > Drop the emergency section from print_irqtrace_events() and enter it > around the call in check_flags(), the only lockdep splat that prints > the irqtrace events outside of one. The other splats and __warn() > already wrap their whole output in an emergency section. > > Fixes: 59cd94ef8009 ("lockdep: Mark emergency sections in lockdep splats") > Suggested-by: John Ogness > Signed-off-by: Breno Leitao Reviewed-by: John Ogness