diff options
| author | Marco Elver <elver@google.com> | 2026-01-30 14:28:24 +0100 |
|---|---|---|
| committer | Sasha Levin <sashal@kernel.org> | 2026-03-04 07:20:51 -0500 |
| commit | 95a6252fc476d882a09b5c67e7ce23104fcb4fe8 (patch) | |
| tree | ed22f07774c7fb3ff55e0c5fbdf50a6ca49bd08c | |
| parent | 7c37920c96b85ef4255a7acc795e99e63dd38d59 (diff) | |
arm64: Fix non-atomic __READ_ONCE() with CONFIG_LTO=y
[ Upstream commit bb0c99e08ab9aa6d04b40cb63c72db9950d51749 ]
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>
Signed-off-by: Sasha Levin <sashal@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 56f7b1d4d54b..bd5fc880b909 100644 --- a/arch/arm64/include/asm/rwonce.h +++ b/arch/arm64/include/asm/rwonce.h @@ -62,7 +62,7 @@ default: \ atomic = 0; \ } \ - atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(__x))__x);\ + atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(*__x) *)__x);\ }) #endif /* !BUILD_VDSO */ |