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Mon, 05 Oct 2026 10:16:41 -0700 (PDT) From: Kunwu Chan To: paulmck@kernel.org, corbet@lwn.net, mingo@redhat.com, frederic@kernel.org, neeraj.upadhyay@kernel.org, josh@joshtriplett.org, urezki@gmail.com, dave@stgolabs.net, lianux.mm@gmail.com Cc: stern@rowland.harvard.edu, parri.andrea@gmail.com, will@kernel.org, peterz@infradead.org, boqun@kernel.org, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, dlustig@nvidia.com, joelagnelf@nvidia.com, skhan@linuxfoundation.org, rdunlap@infradead.org, longman@redhat.com, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang@linux.dev, kunwu.chan@gmail.com, brads@mainlining.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, lkmm@lists.linux.dev, linux-doc@vger.kernel.org, rcu@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH RFC v3 04/15] hazptr: add scoped_guard() support Date: Tue, 6 Oct 2026 01:15:18 +0800 Message-ID: <20261005171529.1378809-5-kunwu.chan@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261005171529.1378809-1-kunwu.chan@gmail.com> References: <20261005171529.1378809-1-kunwu.chan@gmail.com> Precedence: bulk X-Mailing-List: lkmm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add a scoped_guard() class for hazptr so that callers can pair hazptr_acquire() with hazptr_release() on scope exit. The guard holds a pointer to a caller-provided hazptr_ctx rather than embedding it. The ctx must remain at a stable address while the hazard pointer is held because the slow path can chain its backup slot into the overflow list by address. Suggested-by: Boqun Feng Signed-off-by: Kunwu Chan --- include/linux/hazptr.h | 51 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/include/linux/hazptr.h b/include/linux/hazptr.h index d1670121947a..275cbe54b075 100644 --- a/include/linux/hazptr.h +++ b/include/linux/hazptr.h @@ -320,6 +320,57 @@ void hazptr_release(struct hazptr_ctx *ctx, void *addr) hazptr_unchain_backup_slot(ctx); } +/** + * struct hazptr_guard - cleanup.h guard for a single hazard pointer + * + * @ctx: Pointer to the caller-provided hazard-pointer context. + * @addr: The address returned by the matching hazptr_acquire(). + */ +struct hazptr_guard { + struct hazptr_ctx *ctx; + void *addr; +}; + +/** + * hazptr_guard_acquire - Acquire a hazard pointer for scoped_guard() use + * + * @ctx: The caller-provided hazard-pointer context. + * @addr_p: Pointer to the pointer that is to be hazard-pointer protected. + * + * Acquire a hazard pointer using @ctx and return a guard that + * cleanup.h releases via hazptr_release() on scope exit. The guard + * only carries the ctx pointer and the address returned by + * hazptr_acquire(). + */ +static inline struct hazptr_guard +hazptr_guard_acquire(struct hazptr_ctx *ctx, void * const *addr_p) +{ + struct hazptr_guard g; + + g.ctx = ctx; + g.addr = hazptr_acquire(ctx, addr_p); + return g; +} + +DEFINE_CLASS(hazptr, struct hazptr_guard, + hazptr_release(_T.ctx, _T.addr), + hazptr_guard_acquire(ctx, addr_p), + struct hazptr_ctx *ctx, void * const *addr_p) +DEFINE_CLASS_IS_UNCONDITIONAL(hazptr) + +/* + * The ctx must remain at a stable address while the hazard pointer + * is held because the slow path can chain its backup slot + * into the overflow list by address. + * + * struct hazptr_ctx ctx; + * void *obj = ptr; + * + * scoped_guard(hazptr, &ctx, &obj) { + * ... + * } + */ + void hazptr_init(void); #endif /* _LINUX_HAZPTR_H */ -- 2.43.0