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 0N2gC4HF 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Apr 08, 2025 at 02:03:11PM +0300, Dan Carpenter wrote: > Hello Peter Zijlstra, > > This code is old, and so it must work. I can't explain why the warning > is only showing up now. I was just curious what's going on. > > Commit 6d12c8d308e6 ("percpu: Wire up cmpxchg128") from May 31, 2023 > (linux-next), leads to the following Smatch static checker warning: > > mm/slub.c:3609 __update_cpu_freelist_fast() > warn: sizeof(void) > > mm/slub.c > 3599 > 3600 #ifndef CONFIG_SLUB_TINY > 3601 static inline bool > 3602 __update_cpu_freelist_fast(struct kmem_cache *s, > 3603 void *freelist_old, void *freelist_new, > 3604 unsigned long tid) > 3605 { > 3606 freelist_aba_t old = { .freelist = freelist_old, .counter = tid }; > 3607 freelist_aba_t new = { .freelist = freelist_new, .counter = next_tid(tid) }; > 3608 > --> 3609 return this_cpu_try_cmpxchg_freelist(s->cpu_slab->freelist_tid.full, > 3610 &old.full, new.full); > 3611 } > > The problem is: > > arch/arm64/include/asm/percpu.h > 239 #define this_cpu_cmpxchg128(pcp, o, n) \ > 240 ({ \ > 241 typedef typeof(pcp) pcp_op_T__; \ > 242 u128 old__, new__, ret__; \ > 243 pcp_op_T__ *ptr__; \ > 244 old__ = o; \ > 245 new__ = n; \ > 246 preempt_disable_notrace(); \ > 247 ptr__ = raw_cpu_ptr(&(pcp)); \ > 248 ret__ = cmpxchg128_local((void *)ptr__, old__, new__); \ > ^^^^^^^^^^^^^^ > We're passing a void pointer. > > 249 preempt_enable_notrace(); \ > 250 ret__; \ > 251 }) > > include/linux/atomic/atomic-instrumented.h > 5034 #define try_cmpxchg128_local(ptr, oldp, ...) \ > 5035 ({ \ > 5036 typeof(ptr) __ai_ptr = (ptr); \ > 5037 typeof(oldp) __ai_oldp = (oldp); \ > 5038 instrument_atomic_read_write(__ai_ptr, sizeof(*__ai_ptr)); \ > ^^^^^^^^^^^^^^^^^ > Here we're doing a sizeof() of a void pointer which is 1. I think maybe > this is just for KASAN so it's not a big deal in terms of affecting > runtime? As far as I can tell, instrument_* helpers are used to let KASAN/KCSAN/KMSAN check if there are bugs (e.g., KASAN checks shadow memory and determine if this read or write is a memory access violation). When enabled, usually the compiler automatically inserts those checks into the kernel binary. But those helpers are used where the compiler can't. I argue that not being able to precisely catch memory errors for cmpxchg128 users (SLUB and few drivers) has not been a critical problem. But it'd be better to fix it :) > > 5039 instrument_read_write(__ai_oldp, sizeof(*__ai_oldp)); \ > 5040 raw_try_cmpxchg128_local(__ai_ptr, __ai_oldp, __VA_ARGS__); \ > 5041 }) > > > regards, > dan carpenter > -- Cheers, Harry (formerly known as Hyeonggon)