From 6149fc36c09b91050b62e8e68a91027df8df7345 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 2 Jun 2026 11:09:42 +0200 Subject: uaccess: Provide unsafe_atomic_store_release_user() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 --- include/linux/uaccess.h | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'include') diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 56328601218c..c6bd20065a5d 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) -- cgit v1.2.3