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 <[email protected]> Signed-off-by: Kunwu Chan <[email protected]> --- 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
