From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 587444252A2 for ; Tue, 7 Jul 2026 14:34:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=82.195.75.108 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783434893; cv=none; b=Dw2JGClmvnnc2uw5m6x97T+sLmNu6tzt35qD+hp3uFuF5pfaxjsCeDJ6ONiOBuk7oBZ0Jb2PhIYNKCBixZdyg3BSMVQMK4tiOhg94teGRos0Wf8kMn6zrXXIAqglzu8yG3eqFuVNRtALtwhNjbTQzI2YGvHl1h/DyYS7OakJUNc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783434893; c=relaxed/simple; bh=E251A5eHPg1AagbXeAex7KaFDmp/8i+mX6ASUf5QhwY=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=Dqp8AIHEzyVjFBIOgPzNXI58aDm9jvUlZ2cn+SY2ZSeWG9OL+io7z0fcXV6VGqCgYAX/6xpLsJU97sl4WnPCbgJGK/acTu4n0sz07hHdtx6meH5L9tWIq5H4HkUfC387UZM1OosQm5p2SXfuYbzgcmNFQPyvhIdeucLkGeABAv4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org; spf=pass smtp.mailfrom=debian.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b=of9HY9xz; arc=none smtp.client-ip=82.195.75.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=debian.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b="of9HY9xz" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:Content-Transfer-Encoding:Content-Type :MIME-Version:Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID: Content-Description:In-Reply-To:References; bh=xB8yi3BpNm1FHLTqkEQlbeZpuBbC8Hgxnm/71VHpkSw=; b=of9HY9xz5f4GTPEExUNHP12NPD zrXV6YKvBGVtp9ysPkIK2ARmS+bBxHK6QV/gsHBAxchV0DcLRVAMmt2dt3DYE220wLwIcOtWEmpuF 0+/zFZVWo1j4uU6CbK7URzofMS78TTWLwzOHHLOOeltNDOUpx9ULbMWQzFRZbw66ZvphmCQPuNo0T N3Jt4m/M12QmOOMnLlKSOhDmTrhmoIGjSb9Buxx+l+9w8XXaOG/oioPSydKlV1p7KUauB8cP0bzPw SBEKsxZ4ggAvzrpTJ9rf4izEL5ld//Z4NwFkCnZW5ZQPIfbJ4AoymJ+ClG6WZzTMsHp9v0m0WRlG+ RhMJ+WQw==; Received: from authenticated-user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.96) (envelope-from ) id 1wh6sp-002FtU-0h; Tue, 07 Jul 2026 14:34:47 +0000 Date: Tue, 7 Jul 2026 07:34:42 -0700 From: Breno Leitao To: elver@google.com, dvyukov@google.com Cc: kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: RFC: KCSAN single report "feature" Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Debian-User: leitao Hello Marco and KCSAN community KCSAN rate-limits reports so that a given data race is printed at most once per CONFIG_KCSAN_REPORT_ONCE_IN_MS (3s by default): duplicates within that window are dropped, but once it elapses the race is printed again in full. On a long-running machine a persistent race therefore reprints the same multi-line report every few seconds for as long as the racy code runs, flooding dmesg/netconsole with identical reports and drowning out genuinely new ones. Raising REPORT_ONCE_IN_MS only widens the window — the full report still eventually recurs — and setting it to 0 disables rate limiting entirely, so there is no way today to get a race reported just once. I have some debug kernel running in my of Meta fleet, with these debug features and I would like to enable KCSAN, but, this behaviour is flooding our data pipeline. I've recently solved something similar on kmemleak and I am wondering if there is interested in solving something similar on KCSAN. 77d100d11c87e mm/kmemleak: dedupe verbose scan output by allocation backtrace Would it be OK to have a "report once" mode that prints each race once and never re-reports it, maybe exposed as a bool CONFIG_KCSAN_REPORT_ONCE or a kcsan.report_once module parameter ? Thanks, --breno