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| author | Thomas Gleixner <tglx@kernel.org> | 2026-06-02 12:09:42 +0300 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-06-03 12:38:50 +0300 |
| commit | 6149fc36c09b91050b62e8e68a91027df8df7345 (patch) | |
| tree | 3b5e75f60ab755a2f8ef50d863c1cd7c6f225730 | |
| parent | 2cb5251d3d64d57c172185b9b608f704b3015f26 (diff) | |
| download | linux-6149fc36c09b91050b62e8e68a91027df8df7345.tar.xz | |
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 <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Link: https://patch.msgid.link/20260602090535.513181528@kernel.org
| -rw-r--r-- | arch/Kconfig | 4 | ||||
| -rw-r--r-- | include/linux/uaccess.h | 11 |
2 files changed, 15 insertions, 0 deletions
diff --git a/arch/Kconfig b/arch/Kconfig index e86880045158..83d362fca38c 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 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) |