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Wed, 11 Jun 2025 21:20:50 -0700 (PDT) From: Lance Yang X-Google-Original-From: Lance Yang To: akpm@linux-foundation.org Cc: zi.li@linux.dev, anna.schumaker@oracle.com, boqun.feng@gmail.com, joel.granados@kernel.org, jstultz@google.com, kent.overstreet@linux.dev, leonylgao@tencent.com, linux-kernel@vger.kernel.org, longman@redhat.com, mhiramat@kernel.org, mingo@redhat.com, mingzhe.yang@ly.com, peterz@infradead.org, rostedt@goodmis.org, senozhatsky@chromium.org, tfiga@chromium.org, will@kernel.org, Lance Yang Subject: [PATCH RFC 2/3] locking/rwsem: clear reader-owner on unlock to reduce false positives Date: Thu, 12 Jun 2025 12:19:25 +0800 Message-ID: <20250612042005.99602-3-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250612042005.99602-1-lance.yang@linux.dev> References: <20250612042005.99602-1-lance.yang@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: Lance Yang When CONFIG_DETECT_HUNG_TASK_BLOCKER is enabled, a stale owner pointer in a reader-owned rwsem can lead to false positives in blocker tracking. To mitigate this, let=E2=80=99s try to clear the owner field on unlock, as = a NULL owner is better than a stale one for diagnostics. Signed-off-by: Lance Yang --- kernel/locking/rwsem.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 6cb29442d4fc..a310eb9896de 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -205,14 +205,12 @@ bool is_rwsem_reader_owned(struct rw_semaphore *sem) return false; return rwsem_test_oflags(sem, RWSEM_READER_OWNED); } -#endif =20 -#ifdef CONFIG_DEBUG_RWSEMS /* - * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there - * is a task pointer in owner of a reader-owned rwsem, it will be the - * real owner or one of the real owners. The only exception is when the - * unlock is done by up_read_non_owner(). + * With CONFIG_DEBUG_RWSEMS or CONFIG_DETECT_HUNG_TASK_BLOCKER configured, + * it will make sure that the owner field of a reader-owned rwsem either + * points to a real reader-owner(s) or gets cleared. The only exception is + * when the unlock is done by up_read_non_owner(). */ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem) { --=20 2.49.0