On Mon, Jun 07, 2021 at 01:40:02PM +0200, Vlastimil Babka wrote: > On 6/6/21 1:08 PM, Hyeonggon Yoo wrote: > > On Sat, Jun 05, 2021 at 02:10:46PM +0800, kernel test robot wrote: > >> tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master > >> head: ccc252d2e818f6a479441119ad453c3ce7c7c461 > >> commit: a7ba988ff9de37f0961b4bf96d17aca73d0d2e25 [7012/7430] mm, slub: change run-time assertion in kmalloc_index() to compile-time > >> config: parisc-randconfig-r014-20210604 (attached as .config) > >> compiler: hppa-linux-gcc (GCC) 9.3.0 > >> reproduce (this is a W=1 build): > >> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > >> chmod +x ~/bin/make.cross > >> # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=a7ba988ff9de37f0961b4bf96d17aca73d0d2e25 > >> git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git > >> git fetch --no-tags linux-next master > >> git checkout a7ba988ff9de37f0961b4bf96d17aca73d0d2e25 > >> # save the attached .config to linux build tree > >> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=parisc > >> > >> If you fix the issue, kindly add following tag as appropriate > >> Reported-by: kernel test robot <lkp@xxxxxxxxx> > >> > >> All errors (new ones prefixed by >>): > >> In file included from <command-line>: > >> In function 'kmalloc_index', > >> inlined from 'kmalloc_node' at include/linux/slab.h:572:20, > >> inlined from 'bpf_map_kmalloc_node.isra.0.part.0' at include/linux/bpf.h:1319:9: > >> >> include/linux/compiler_types.h:328:38: error: call to '__compiletime_assert_183' declared with attribute error: unexpected size in kmalloc_index() > >> 328 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) > >> | ^ > >> include/linux/compiler_types.h:309:4: note: in definition of macro '__compiletime_assert' > >> 309 | prefix ## suffix(); \ > >> | ^~~~~~ > >> include/linux/compiler_types.h:328:2: note: in expansion of macro '_compiletime_assert' > >> 328 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) > >> | ^~~~~~~~~~~~~~~~~~~ > >> include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert' > >> 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) > >> | ^~~~~~~~~~~~~~~~~~ > >> include/linux/slab.h:389:2: note: in expansion of macro 'BUILD_BUG_ON_MSG' > >> 389 | BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()"); > >> | ^~~~~~~~~~~~~~~~ > > > > Reproduce with attached config, and read the code. > > It has no problem in clang (clang-10/clang-11). it is problem with gcc. > > But what exactly is the gcc problem here? > Did you have to reproduce it with specific gcc version and/or architecture? > Before replying, I should say that I'm not an expert on gcc. I just tried some ways to fix the error, and it seemed to me that gcc is doing something wrong. I found the error was in kernel/bpf/local_storage.c and I copied the bot's config in linux-next (20210607), and just entered all new config. running 'make kernel/bpf/local_storage.o CC=gcc' can reproduce the error. the bot says it is error with parisc, but I was able to reproduce it in my x86 machine. I tested on gcc-9.3.0 and gcc-10.2.0 both makes an error, and clang 10.0.1, clang 11.0.0 didn't make an error. > > I found two ways to solve the error (maybe there would be better > > solution) Any thoughts or opinions? > > > > > > First ways is to change condition of kmalloc_index macro. > > > > diff --git a/include/linux/slab.h b/include/linux/slab.h > > index 70e46db766ca..be2c900cba4b 100644 > > --- a/include/linux/slab.h > > +++ b/include/linux/slab.h > > @@ -397,7 +397,7 @@ static __always_inline unsigned int __kmalloc_index(size_t size, > > /* Will never be reached. Needed because the compiler may complain */ > > return -1; > > } > > -#define kmalloc_index(s) __kmalloc_index(s, true) > > +#define kmalloc_index(s) __kmalloc_index(s, __builtin_constant_p(s) && true) > > I wonder how this extra guard can possibly matter? > > bpf_map_kmalloc_node() > kmalloc_node() > if (__builtin_constant_p(size) ...) > unsigned int i = kmalloc_index(size); > > We shouldn't be even reaching kmalloc_index() unless __builtin_constant_p(size) > is already true. Yes, I knew that when I wrote the code. That totally doesn't make sense. why __builtin_constant_p(size) was true in kmalloc_node, and false in the evalaution (__builtin_constant_p(s) && true)? but it actually solves the error. At this point, I thought gcc was doing something wrong.... Well, I know we need more evidence to conclude gcc is wrong. (Or we made wrong code that makes compiler confusing.) I want to hear you and some other people's opinion. > > #endif /* !CONFIG_SLOB */ > > > > void *__kmalloc(size_t size, gfp_t flags) __assume_kmalloc_alignment __malloc; > > > > > > Second way is making bpf_map_kmalloc_node always inline. > > If bpf_map_kmalloc_node() is not being compiled as inline, how can it possibly > evaluate __builtin_constant_p(size) as true when processing the inlined > kmalloc_node()? As I said above - it doesn't make sense, but gcc is acting differently on __inline and inline, in bpf_map_kmalloc_node function. just making bpf_map_kmalloc_node always solves the error, but I have no clue WHY... anyway, in summary: - the diff I sent should not make sense, but it works for gcc. - So I think gcc is doing something wrong (but more evidence needed) I can be missing something. So If I said something wrong, or if you can't reproduce the error, please tell me! Thanks, Hyeonggon Yoo > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > index 02b02cb29ce2..09379d705349 100644 > > --- a/include/linux/bpf.h > > +++ b/include/linux/bpf.h > > @@ -1312,7 +1312,7 @@ void *bpf_map_kzalloc(const struct bpf_map *map, size_t size, gfp_t flags); > > void __percpu *bpf_map_alloc_percpu(const struct bpf_map *map, size_t size, > > size_t align, gfp_t flags); > > #else > > -static inline void * > > +static __always_inline void * > > bpf_map_kmalloc_node(const struct bpf_map *map, size_t size, gfp_t flags, > > int node) > > { > > >
