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[209.85.216.47]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c858dc653e1sm1986662a12.12.2026.05.30.10.38.36 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 30 May 2026 10:38:36 -0700 (PDT) Received: by mail-pj1-f47.google.com with SMTP id 98e67ed59e1d1-36bd175fdbaso814889a91.0 for ; Sat, 30 May 2026 10:38:36 -0700 (PDT) X-Received: by 2002:a17:90a:fc4c:b0:36b:e109:1e63 with SMTP id 98e67ed59e1d1-36c685a8f89mr4221965a91.27.1780162716537; Sat, 30 May 2026 10:38:36 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Dennis Moshegov Date: Sat, 30 May 2026 18:38:23 +0100 X-Gmail-Original-Message-ID: X-Gm-Features: AVHnY4JNU7hA7t2ZTnjRQe_V1OCI_cd0KEoVyFsUA967NMFjwJObFlVCPbO52Ag Message-ID: Subject: [PATCH] timekeeping: Use data_race() and READ_ONCE() in ktime_get_real_seconds() To: john.stultz@linaro.org, tglx@linutronix.de Cc: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Dennis Moshegov Subject: [PATCH] timekeeping: Use data_race() and READ_ONCE() in ktime_get_real_seconds() On 64-bit architectures, ktime_get_real_seconds() directly returns tk_core.timekeeper.xtime_sec without acquiring a seqlock. This lockless read is an intentional design choice optimized for ultra-fast, approximate timestamping paths where a minor 1-second discrepancy is acceptable. However, Kernel Concurrency Sanitizer (KCSAN) flags a data race here because the timekeeper structure is updated concurrently via a bulk structure copy inside timekeeping_update_from_shadow() during timer interrupts. Since the 64-bit read is naturally aligned and atomic at the hardware level, this data race is benign and does not cause data tearing. Annotate the read path using data_race() combined with READ_ONCE() to prevent compiler optimization anomalies and suppress the KCSAN warning. Reported-by: syzbot+72789cd1697965e714ca@syzkaller.appspotmail.com Closes: https://syzkaller.appspotmail.com/bug?extid=3D72789cd1697965e714ca Assisted-by: Gemini:3.5-flash Signed-off-by: Dennis Moshegov --- kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 4fd3c70c1..b2e5a87da 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1153,7 +1153,7 @@ time64_t ktime_get_real_seconds(void) time64_t ktime_get_real_seconds(void) { #if BITS_PER_LONG =3D=3D 64 - return tk_core.timekeeper.xtime_sec; + return data_race(READ_ONCE(tk_core.timekeeper.xtime_sec)); #else unsigned int seq; time64_t seconds; --=20 2.43.0