From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 7EEF6179FD7; Sun, 24 Mar 2024 23:41:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711323666; cv=none; b=bGqoCdabsyDKF+6GBd38aHM72l5l5RbilgDaW1riUyIZsBB8ALAu8nz+ZtYMglxk5Q9sOGR301lIBIab27Kt21kl4ZMzafTa/4M9m3E6QGWOjD7vq/9fp4/oODR+1Kgmv1mKODmn0H8cZWRnpeSxyanVeYqlDmQtfUhY0jURKfU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711323666; c=relaxed/simple; bh=7qg2d7U5uXac9tRrTtTU0XxUPVPsUuSatmmbjlFPExQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=O5VMe6y+ugV+rEuIy9nhN6Z1JqCeC8SFlbxSGjk9YaY1WdVtBMv9xp4nM3mIvojyYChHwfSZuXGvwzYYz/rVuaKb4sCxmO5CEdFlHSn03UM/i5CILwyfBVvk6eWzxYGr3ZXleJ4EJVX5wsiBWMs1lMW0uAS4M9V6aME5ywFmHgo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KE7/TzL+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="KE7/TzL+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B9692C433C7; Sun, 24 Mar 2024 23:41:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711323665; bh=7qg2d7U5uXac9tRrTtTU0XxUPVPsUuSatmmbjlFPExQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KE7/TzL+bBK5w+VzTrKBB39TOhJQdZpOuwnrWYnUiGEDjhRydDiuZvMSacL8qxiAg XAnztY8UM9E78687qJqhtiYiPs7iOYpf41x9/LFa0djZNBKzKjtqxb0igtfxyskzPO dMEam0yDzP3mL6gWen4lEvTK0vxs0wNBTECldesaYZYsvw9ccidABOaNC2RDT12Loh +gZeQ9v9VKx2Mt6KfHPil7aRue/SQvw9IIW9CF+iqqBxdjU8Lou6j9IKgRF3WE9fn1 kvxI1oENQVBIovqbgxXSIdJrhUjVxEHsi82N3k+Zi3l5sZOZje1MSMnKOjE+/UAKOS CewvYKoFIV+pA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Peter Hilber , Thomas Gleixner , Sasha Levin Subject: [PATCH 5.10 037/238] timekeeping: Fix cross-timestamp interpolation corner case decision Date: Sun, 24 Mar 2024 19:37:05 -0400 Message-ID: <20240324234027.1354210-38-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240324234027.1354210-1-sashal@kernel.org> References: <20240324234027.1354210-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit From: Peter Hilber [ Upstream commit 87a41130881995f82f7adbafbfeddaebfb35f0ef ] 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 Signed-off-by: Sasha Levin --- 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 6a8a610b19717..6f615db414769 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1167,13 +1167,15 @@ 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; } @@ -1233,7 +1235,7 @@ 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; @@ -1264,13 +1266,13 @@ 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; -- 2.43.0