Hi Andrii,

I love your patch! Yet something to improve:

[auto build test ERROR on bpf-next/master]
[also build test ERROR on next-20200512]
[cannot apply to bpf/master rcu/dev v5.7-rc5]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Andrii-Nakryiko/BPF-ring-buffer/20200514-032857
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: sh-allmodconfig (attached as .config)
compiler: sh4-linux-gcc (GCC) 9.3.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day GCC_VERSION=9.3.0 make.cross ARCH=sh 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot <redacted>

All error/warnings (new ones prefixed by >>):

In file included from include/linux/kernel.h:11,
from include/linux/list.h:9,
from include/linux/timer.h:5,
from include/linux/workqueue.h:9,
from include/linux/bpf.h:9,
from kernel/bpf/ringbuf.c:1:
kernel/bpf/ringbuf.c: In function 'bpf_ringbuf_commit':

quoted

include/linux/compiler.h:350:38: error: call to '__compiletime_assert_134' declared with attribute error: Need native word sized stores/loads for atomicity.

350 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
|                                      ^
include/linux/compiler.h:331:4: note: in definition of macro '__compiletime_assert'
331 |    prefix ## suffix();             |    ^~~~~~
include/linux/compiler.h:350:2: note: in expansion of macro '_compiletime_assert'
350 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
|  ^~~~~~~~~~~~~~~~~~~
include/linux/compiler.h:353:2: note: in expansion of macro 'compiletime_assert'
353 |  compiletime_assert(__native_word(t),             |  ^~~~~~~~~~~~~~~~~~
include/asm-generic/barrier.h:187:2: note: in expansion of macro 'compiletime_assert_atomic_type'
187 |  compiletime_assert_atomic_type(*p);             |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

quoted

kernel/bpf/ringbuf.c:354:13: note: in expansion of macro 'smp_load_acquire'

354 |  cons_pos = smp_load_acquire(&rb->consumer_pos) & rb->mask;
|             ^~~~~~~~~~~~~~~~

vim +/smp_load_acquire +354 kernel/bpf/ringbuf.c

   332	
   333	static void bpf_ringbuf_commit(void *sample, bool discard)
   334	{
   335		unsigned long rec_pos, cons_pos;
   336		u32 new_meta, old_meta;
   337		void *meta_ptr;
   338		struct bpf_ringbuf *rb;
   339	
   340		meta_ptr = sample - RINGBUF_META_SZ;
   341		rb = bpf_ringbuf_restore_from_rec(meta_ptr);
   342		old_meta = *(u32 *)meta_ptr;
   343		new_meta = old_meta ^ RINGBUF_BUSY_BIT;
   344		if (discard)
   345			new_meta |= RINGBUF_DISCARD_BIT;
   346	
   347		/* update metadata header with correct final size prefix */
   348		xchg((u32 *)meta_ptr, new_meta);
   349	
   350		/* if consumer caught up and is waiting for our record, notify about
   351		 * new data availability
   352		 */
   353		rec_pos = (void *)meta_ptr - (void *)rb->data;
 > 354		cons_pos = smp_load_acquire(&rb->consumer_pos) & rb->mask;
   355		if (cons_pos == rec_pos)
   356			wake_up_all(&rb->waitq);
   357	}
   358	

---
0-DAY CI Kernel Test Service, Intel Corporation
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