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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , Jonathan Corbet , Shuah Khan , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, rust-for-linux@vger.kernel.org, linux-kbuild@vger.kernel.org, llvm@lists.linux.dev, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, workflows@vger.kernel.org, linux-doc@vger.kernel.org, Yeoreum Yun , Yunseong Kim , Yunseong Kim References: <20260611-b4-kcov-dataflow-v2-v2-0-0a261da3987c@est.tech> <20260611-b4-kcov-dataflow-v2-v2-3-0a261da3987c@est.tech> From: Yunseong Kim Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: LO2P123CA0082.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:138::15) To AS8P189MB1752.EURP189.PROD.OUTLOOK.COM (2603:10a6:20b:39b::19) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: AS8P189MB1752:EE_|VI0P189MB3236:EE_ X-MS-Office365-Filtering-Correlation-Id: 21059141-36fb-4598-f95f-08dec881f026 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|23010399003|376014|7416014|18002099003|22082099003|6133799003|11063799006|56012099006|4143699003; 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Without compiler barriers, the guard set/clear >> can be reordered relative to the function body, making the protection >> ineffective under optimization. >> >> Add barrier() after setting the guard and before clearing it, ensuring >> the compiler does not move instrumented operations outside the guarded >> region. >> >> Cc: Peter Zijlstra >> Signed-off-by: Yunseong Kim >> --- >> kernel/kcov_dataflow.c | 2 ++ > > Please merge this patch into the one introducing kcov_dataflow.c > Understood. I'll merge them in v3. >> 1 file changed, 2 insertions(+) >> >> diff --git a/kernel/kcov_dataflow.c b/kernel/kcov_dataflow.c >> index df7e8bf70bfa..5248293280d5 100644 >> --- a/kernel/kcov_dataflow.c >> +++ b/kernel/kcov_dataflow.c >> @@ -86,6 +86,7 @@ kcov_df_write(u64 type_marker, u64 pc, u64 meta, void *ptr, >> if (t->kcov_df_seq & (1U << 31)) >> return; >> t->kcov_df_seq |= (1U << 31); >> + barrier(); > > Please make sure barriers have comments explaining which barriers they > pair with (see kernel/kcov.c) Thanks for the pointer. I see the existing implementation now and will align my changes with it. Best regards, Yunseong