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 90C2D762FF; Sun, 24 Mar 2024 22:35:49 +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=1711319749; cv=none; b=neQoP8WSqFfdoHekdymVE8hsXYlzE28GjffolTE1LvvnRPSg4Ic27xIy7Q7FHtXKizVOQzQGfrIhD436ao3HRZSiN3OOqKD3Tpea7JVK6tsZJd1SN2m9qp7t8FJXBmbqV6jzlz2E3xrgHNoXsjYqhgDcIBqgDkgsxi+bkTpJ/b0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711319749; c=relaxed/simple; bh=OrTxKuavkmAwp8h1Jo3aMTmD6H5/LjHaoUEWZ+XZ/aQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=M96vuT1ZNQmNmn0OS2kQ2k6DwKm2GIsy3koOkl402+9wvYFzpuIPaSrhYqNJtO+oksr1E+Kc1gyAbbr/mIanPVyTb5GWcmYt97B13vX5RuBNr2YeGrakmz9E7exDaC1fdtnGHE3e3yQAEhzu3HLtXIP/T3wMhCr3HCCF3wPCy+Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=g0gv85sZ; 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="g0gv85sZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE2DFC433F1; Sun, 24 Mar 2024 22:35:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711319749; bh=OrTxKuavkmAwp8h1Jo3aMTmD6H5/LjHaoUEWZ+XZ/aQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=g0gv85sZMGw3Lh4HL0pgB1Bw1hQtFdSVDyOh0LkqVRl+MBw6TYVoUv03GBNmR5z/P fchC/KmkIx5SnmXtWoOlohay6UwJUG1e6NXeY0PKUq1NuhWdUGH8dGS+7QQvMfdhmf EzNrQZyOK4YJt6C5T6osrwupmPjJy09ooPkyZXEr3ViAJe8YHEvhlDuE/Opch5gIgf s/i8fL7IPTJTTwhc0+bYUz707siN2L/TlT8jCb0KlY+hHF3ToT5LbupF/cOgv7EIah dSTqaAZCMLCR8otyy2O2b0z2T+CbdEBw1Mg0Pq5XroqszHAOV5nbiZgipDeLIbAgMv tRK9vDGsdbslw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Peter Hilber , Thomas Gleixner , Sasha Levin Subject: [PATCH 6.8 050/715] timekeeping: Fix cross-timestamp interpolation corner case decision Date: Sun, 24 Mar 2024 18:23:49 -0400 Message-ID: <20240324223455.1342824-51-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240324223455.1342824-1-sashal@kernel.org> References: <20240324223455.1342824-1-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 8f35455b62509..4e9f2f88c9d6e 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; -- 2.43.0