From 093d9b240a1fa261ff8aeb7c7cc484dedacfda53 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Wed, 7 Jun 2023 14:20:59 -0700 Subject: [PATCH] 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 Signed-off-by: Nathan Chancellor Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20230607-fix-shadowing-in-raw_cpu_generic_try_cmpxchg-v1-1-8f0a3d930d43@kernel.org --- 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 68c410e85cd7..94cbd50cc870 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 { \