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Hall" Subject: [RFC PATCH 2/7] timekeeping: Fix cross-timestamp interpolation corner case decision Date: Fri, 30 Jun 2023 19:10:45 +0200 Message-Id: <20230630171052.985577-3-peter.hilber@opensynergy.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230630171052.985577-1-peter.hilber@opensynergy.com> References: <20230630171052.985577-1-peter.hilber@opensynergy.com> MIME-Version: 1.0 X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DB8EUR05FT043:EE_|BEZP281MB1879:EE_ X-MS-Office365-Filtering-Correlation-Id: ebcbff29-e16f-4686-b065-08db798d2e7f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:217.66.60.4;CTRY:DE;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:SR-MAIL-03.open-synergy.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230028)(346002)(136003)(39840400004)(376002)(396003)(451199021)(36840700001)(46966006)(336012)(47076005)(83380400001)(2616005)(2906002)(81166007)(36860700001)(40480700001)(36756003)(8936002)(8676002)(82310400005)(5660300002)(86362001)(54906003)(41300700001)(6916009)(4326008)(70206006)(70586007)(316002)(478600001)(42186006)(186003)(44832011)(1076003)(26005)(36900700001);DIR:OUT;SFP:1102; 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So far, cycle_between() checks if parameter test is in the open interval (before, after), when disregarding the special case before > after. The only cycle_between() user, get_device_system_crosststamp(), has the following problem with this: If interval_start == cycles, cycle_between(interval_start, cycles, now) returns false. If a history_begin was supplied to get_device_system_crosststamp(), it will later call cycle_between() again, with effective argument values cycle_between(history_begin->cycles, cycles, cycles). Due to the test against the open interval, cycle_between() returns false again, and get_device_system_crosststamp() returns -EINVAL, when it could have succeeded. Fix this by testing against the closed interval in cycle_between(). This disables interpolation if interval_start == cycles. For the special case before > after, similar arguments hold. Fix this in a similar way. At the second cycle_between() call site, add an extra condition in order to effectively check a half-open interval, which keeps the condition documented above the call site satisfied. Fixes: 2c756feb18d9 ("time: Add history to cross timestamp interface supporting slower devices") Signed-off-by: Peter Hilber --- kernel/time/timekeeping.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 8f35455b6250..7e86d5cd784d 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1180,13 +1180,13 @@ static int adjust_historical_crosststamp(struct system_time_snapshot *history, } /* - * cycle_between - true if test occurs chronologically between before and after + * cycle_between - true if test occurs chronologically in [before, after] */ static bool cycle_between(u64 before, u64 test, u64 after) { - if (test > before && test < after) + if (test >= before && test <= after) return true; - if (before > after && (test > before || test < after)) + if (before > after && (test >= before || test <= after)) return true; return false; } @@ -1282,6 +1282,7 @@ int get_device_system_crosststamp(int (*get_time_fn) * clocksource change */ if (!history_begin || + history_begin->cycles == system_counterval.cycles || !cycle_between(history_begin->cycles, system_counterval.cycles, cycles) || history_begin->cs_was_changed_seq != cs_was_changed_seq)