From: Thomas Gleixner Date: Tue, 2 Jun 2026 09:09:42 +0000 (+0200) Subject: uaccess: Provide unsafe_atomic_store_release_user() X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=6149fc36c09b91050b62e8e68a91027df8df7345;p=thirdparty%2Fkernel%2Flinux.git uaccess: Provide unsafe_atomic_store_release_user() The upcoming support for unlocking robust futexes in the kernel requires store release semantics. Syscalls do not imply memory ordering on all architectures so the unlock operation requires a barrier. This barrier can be avoided when stores imply release like on x86. Provide a generic version with a smp_mb() before the unsafe_put_user(), which can be overridden by architectures. Provide also a ARCH_MEMORY_ORDER_TSO Kconfig option, which can be selected by architectures with Total Store Order (TSO), where store implies release, so that the smp_mb() in the generic implementation can be avoided. If that is set a barrier() is used instead of smp_mb(), which is not required for the use case at hand, but makes it future proof for other usage to prevent the compiler from reordering. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: André Almeida Link: https://patch.msgid.link/20260602090535.513181528@kernel.org --- diff --git a/arch/Kconfig b/arch/Kconfig index e86880045158e..83d362fca38cd 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -403,6 +403,10 @@ config ARCH_32BIT_OFF_T config ARCH_32BIT_USTAT_F_TINODE bool +# Selected by architectures with Total Store Order (TSO) +config ARCH_MEMORY_ORDER_TSO + bool + config HAVE_ASM_MODVERSIONS bool help diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 56328601218c5..c6bd20065a5d7 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -649,6 +649,17 @@ static inline void user_access_restore(unsigned long flags) { } #define user_read_access_end user_access_end #endif +#ifndef unsafe_atomic_store_release_user +# define unsafe_atomic_store_release_user(val, uptr, elbl) \ + do { \ + if (!IS_ENABLED(CONFIG_ARCH_MEMORY_ORDER_TSO)) \ + smp_mb(); \ + else \ + barrier(); \ + unsafe_put_user(val, uptr, elbl); \ + } while (0) +#endif + /* Define RW variant so the below _mode macro expansion works */ #define masked_user_rw_access_begin(u) masked_user_access_begin(u) #define user_rw_access_begin(u, s) user_access_begin(u, s)