From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 DA2EA3F8DA; Mon, 19 Feb 2024 16:35:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708360520; cv=none; b=pPWTKRQXSAp4X2AybWUZhYs9TKK8bJXaD2sjK4FFINE/AN0eRJEK3eK5njODBF4IXNzlxezw/BeWVn+Knx4U0auzDObJgvz02zWg/VHtQVIg4ndOLC1MfXC1BQRuUY9Bu6k0ZlyYHAUlHb1/I4xlGFTd8mG2TeROmwFLenq2vyQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708360520; c=relaxed/simple; bh=A7kkVstefmy/G8B3QJ5+gmq/tloozB0WcNaV/YC4/Sw=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=X2ddckyBPrymPZwrpnfhbPHxHuSqoFKUDahYTDK+u22eUKpL8LgQppl/Oaf/LIf+yJP5VH601xWJQsXc+mF3Av3DPxmAo31UTkLMplnnHUPPpWJhfIklL/CXi2edagBG8fk7qzaHyeSH+LSJCf8qPfoOuWQya3ub5RyqkuYMNH8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=fd5pl+gp; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=hL9/S4dy; arc=none smtp.client-ip=193.142.43.55 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.b="fd5pl+gp"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="hL9/S4dy" Date: Mon, 19 Feb 2024 16:35:16 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1708360517; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=W9CTE6txggKbm42VGWt32hCnmGwsNogqpM5Wl2vVBq8=; b=fd5pl+gpmswO0nicu766KBiuNOPygF5xbNWjMu28TEB4NXbWnKJiET9ODkZulQiIddMpjM t7lsTlgZXkrlJ+SscOMSAxUejz76JSIrHE70VHXd30Gn5ijljehuMhH+o9Xprvv0RRSEOF AN0+ZEFfplJdVLbSwcVcm8d6PVaLei4+cCQAqMCEM4957agnHkMjo1eibKlZGytulD4mhP vTNfXn2r8TiA4vv6LWjWlmWeYF/MOFpCu8pmEIYn0+lnsUUzKUiVsBFJryW56xnxuiX3/G 1StauiljM+FeIF7P8brPiwhtylScT14fhiea5ntreXMjGG0Qw/QOla3Hof0nHw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1708360517; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=W9CTE6txggKbm42VGWt32hCnmGwsNogqpM5Wl2vVBq8=; b=hL9/S4dyuaJSDE5iuZ9xftE6fzzDUjubplgV34tNj5e/DqRZjNscmUdNGJE4iGMZFr9Gpb UV75kbgKgjnCCmDg== From: "tip-bot2 for Peter Hilber" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/core] timekeeping: Fix cross-timestamp interpolation corner case decision Cc: Peter Hilber , Thomas Gleixner , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20231218073849.35294-3-peter.hilber@opensynergy.com> References: <20231218073849.35294-3-peter.hilber@opensynergy.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <170836051645.398.6755085884635470259.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit The following commit has been merged into the timers/core branch of tip: Commit-ID: 87a41130881995f82f7adbafbfeddaebfb35f0ef Gitweb: https://git.kernel.org/tip/87a41130881995f82f7adbafbfeddaebfb35f0ef Author: Peter Hilber AuthorDate: Mon, 18 Dec 2023 08:38:40 +01:00 Committer: Thomas Gleixner CommitterDate: Mon, 19 Feb 2024 12:18:51 +01:00 timekeeping: Fix cross-timestamp interpolation corner case decision The cycle_between() helper checks if parameter test is in the open interval (before, after). Colloquially speaking, this also applies to the counter wrap-around special case before > after. get_device_system_crosststamp() currently uses cycle_between() at the first call site to decide whether to interpolate for older counter readings. get_device_system_crosststamp() has the following problem with cycle_between() testing against an open interval: Assume that, by chance, cycles == tk->tkr_mono.cycle_last (in the following, "cycle_last" for brevity). Then, cycle_between() at the first call site, with effective argument values cycle_between(cycle_last, cycles, now), returns false, enabling interpolation. During interpolation, get_device_system_crosststamp() will then call cycle_between() at the second call site (if a history_begin was supplied). The effective argument values are cycle_between(history_begin->cycles, cycles, cycles), since system_counterval.cycles == interval_start == cycles, per the assumption. Due to the test against the open interval, cycle_between() returns false again. This causes get_device_system_crosststamp() to return -EINVAL. This failure should be avoided, since get_device_system_crosststamp() works both when cycles follows cycle_last (no interpolation), and when cycles precedes cycle_last (interpolation). For the case cycles == cycle_last, interpolation is actually unneeded. Fix this by changing cycle_between() into timestamp_in_interval(), which now checks against the closed interval, rather than the open interval. This changes the get_device_system_crosststamp() behavior for three corner cases: 1. Bypass interpolation in the case cycles == tk->tkr_mono.cycle_last, fixing the problem described above. 2. At the first timestamp_in_interval() call site, cycles == now no longer causes failure. 3. At the second timestamp_in_interval() call site, history_begin->cycles == system_counterval.cycles no longer causes failure. adjust_historical_crosststamp() also works for this corner case, where partial_history_cycles == total_history_cycles. These behavioral changes should not cause any problems. Fixes: 2c756feb18d9 ("time: Add history to cross timestamp interface supporting slower devices") Signed-off-by: Peter Hilber Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20231218073849.35294-3-peter.hilber@opensynergy.com --- kernel/time/timekeeping.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 8f35455..4e9f2f8 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1180,13 +1180,15 @@ static int adjust_historical_crosststamp(struct system_time_snapshot *history, } /* - * cycle_between - true if test occurs chronologically between before and after + * timestamp_in_interval - true if ts is chronologically in [start, end] + * + * True if ts occurs chronologically at or after start, and before or at end. */ -static bool cycle_between(u64 before, u64 test, u64 after) +static bool timestamp_in_interval(u64 start, u64 end, u64 ts) { - if (test > before && test < after) + if (ts >= start && ts <= end) return true; - if (before > after && (test > before || test < after)) + if (start > end && (ts >= start || ts <= end)) return true; return false; } @@ -1246,7 +1248,7 @@ int get_device_system_crosststamp(int (*get_time_fn) */ now = tk_clock_read(&tk->tkr_mono); interval_start = tk->tkr_mono.cycle_last; - if (!cycle_between(interval_start, cycles, now)) { + if (!timestamp_in_interval(interval_start, now, cycles)) { clock_was_set_seq = tk->clock_was_set_seq; cs_was_changed_seq = tk->cs_was_changed_seq; cycles = interval_start; @@ -1277,13 +1279,13 @@ int get_device_system_crosststamp(int (*get_time_fn) bool discontinuity; /* - * Check that the counter value occurs after the provided + * Check that the counter value is not before the provided * history reference and that the history doesn't cross a * clocksource change */ if (!history_begin || - !cycle_between(history_begin->cycles, - system_counterval.cycles, cycles) || + !timestamp_in_interval(history_begin->cycles, + cycles, system_counterval.cycles) || history_begin->cs_was_changed_seq != cs_was_changed_seq) return -EINVAL; partial_history_cycles = cycles - system_counterval.cycles;