The following commit has been merged into the locking/core branch of tip:
Commit-ID: 093d9b240a1fa261ff8aeb7c7cc484dedacfda53
Gitweb: https://git.kernel.org/tip/093d9b240a1fa261ff8aeb7c7cc484dedacfda53
Author: Nathan Chancellor <nathan@xxxxxxxxxx>
AuthorDate: Wed, 07 Jun 2023 14:20:59 -07:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 08 Jun 2023 10:28:39 +02:00
percpu: Fix self-assignment of __old in raw_cpu_generic_try_cmpxchg()
After commit c5c0ba953b8c ("percpu: Add {raw,this}_cpu_try_cmpxchg()"),
clang built ARCH=arm and ARCH=arm64 kernels with CONFIG_INIT_STACK_NONE
started panicking on boot in alloc_vmap_area():
[ 0.000000] kernel BUG at mm/vmalloc.c:1638!
[ 0.000000] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.4.0-rc2-ARCH+ #1
[ 0.000000] Hardware name: linux,dummy-virt (DT)
[ 0.000000] pstate: 200000c9 (nzCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 0.000000] pc : alloc_vmap_area+0x7ec/0x7f8
[ 0.000000] lr : alloc_vmap_area+0x7e8/0x7f8
Compiling mm/vmalloc.c with W=2 reveals an instance of -Wshadow, which
helps uncover that through macro expansion, '__old = *(ovalp)' in
raw_cpu_generic_try_cmpxchg() can become '__old = *(&__old)' through
raw_cpu_generic_cmpxchg(), which results in garbage being assigned to
the inner __old and the cmpxchg not working properly.
Add an extra underscore to __old in raw_cpu_generic_try_cmpxchg() so
that there is no more self-assignment, which resolves the panics.
Closes: https://github.com/ClangBuiltLinux/linux/issues/1868
Fixes: c5c0ba953b8c ("percpu: Add {raw,this}_cpu_try_cmpxchg()")
Debugged-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20230607-fix-shadowing-in-raw_cpu_generic_try_cmpxchg-v1-1-8f0a3d930d43@xxxxxxxxxx
---
include/asm-generic/percpu.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index 68c410e..94cbd50 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -101,9 +101,9 @@ do { \
#define raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval) \
({ \
typeof(pcp) *__p = raw_cpu_ptr(&(pcp)); \
- typeof(pcp) __val = *__p, __old = *(ovalp); \
+ typeof(pcp) __val = *__p, ___old = *(ovalp); \
bool __ret; \
- if (__val == __old) { \
+ if (__val == ___old) { \
*__p = nval; \
__ret = true; \
} else { \
|