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| author | Marco Elver <elver@google.com> | 2026-01-30 16:28:24 +0300 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2026-02-02 18:40:54 +0300 |
| commit | bb0c99e08ab9aa6d04b40cb63c72db9950d51749 (patch) | |
| tree | e166aa158c02913f7cbb4836b25e35804a1b86d3 | |
| parent | 76e9f683a53186775af1610b734b51383a17eb70 (diff) | |
| download | linux-bb0c99e08ab9aa6d04b40cb63c72db9950d51749.tar.xz | |
arm64: Fix non-atomic __READ_ONCE() with CONFIG_LTO=y
The implementation of __READ_ONCE() under CONFIG_LTO=y incorrectly
qualified the fallback "once" access for types larger than 8 bytes,
which are not atomic but should still happen "once" and suppress common
compiler optimizations.
The cast `volatile typeof(__x)` applied the volatile qualifier to the
pointer type itself rather than the pointee. This created a volatile
pointer to a non-volatile type, which violated __READ_ONCE() semantics.
Fix this by casting to `volatile typeof(*__x) *`.
With a defconfig + LTO + debug options build, we see the following
functions to be affected:
xen_manage_runstate_time (884 -> 944 bytes)
xen_steal_clock (248 -> 340 bytes)
^-- use __READ_ONCE() to load vcpu_runstate_info structs
Fixes: e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y")
Cc: stable@vger.kernel.org
Reviewed-by: Boqun Feng <boqun@kernel.org>
Signed-off-by: Marco Elver <elver@google.com>
Tested-by: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Will Deacon <will@kernel.org>
| -rw-r--r-- | arch/arm64/include/asm/rwonce.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h index 78beceec10cd..fc0fb42b0b64 100644 --- a/arch/arm64/include/asm/rwonce.h +++ b/arch/arm64/include/asm/rwonce.h @@ -58,7 +58,7 @@ default: \ atomic = 0; \ } \ - atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(__x))__x);\ + atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(*__x) *)__x);\ }) #endif /* !BUILD_VDSO */ |