Re: [PATCH] tracing: Fix to avoid wakeup loop in splice read of per-cpu buffer

From: kernel test robot
Date: Tue Aug 22 2023 - 00:02:32 EST

Hi Masami,

kernel test robot noticed the following build warnings:

[auto build test WARNING on linus/master]
[also build test WARNING on v6.5-rc7 next-20230821]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url: https://github.com/intel-lab-lkp/linux/commits/Masami-Hiramatsu-Google/tracing-Fix-to-avoid-wakeup-loop-in-splice-read-of-per-cpu-buffer/20230821-222307
base: linus/master
patch link: https://lore.kernel.org/r/169262755804.106231.8245792908363050528.stgit%40devnote2
patch subject: [PATCH] tracing: Fix to avoid wakeup loop in splice read of per-cpu buffer
config: mips-allyesconfig (https://download.01.org/0day-ci/archive/20230822/202308221154.hil5JaxI-lkp@xxxxxxxxx/config)
compiler: mips-linux-gcc (GCC) 12.3.0
reproduce: (https://download.01.org/0day-ci/archive/20230822/202308221154.hil5JaxI-lkp@xxxxxxxxx/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202308221154.hil5JaxI-lkp@xxxxxxxxx/

All warnings (new ones prefixed by >>):

In file included from arch/mips/include/asm/div64.h:89,
from include/linux/math.h:6,
from include/linux/math64.h:6,
from include/linux/time64.h:5,
from include/linux/restart_block.h:10,
from include/linux/thread_info.h:14,
from include/asm-generic/preempt.h:5,
from ./arch/mips/include/generated/asm/preempt.h:1,
from include/linux/preempt.h:79,
from include/linux/spinlock.h:56,
from include/linux/mmzone.h:8,
from include/linux/gfp.h:7,
from include/linux/mm.h:7,
from include/linux/ring_buffer.h:5,
from kernel/trace/trace.c:15:
kernel/trace/trace.c: In function 'tracing_buffers_splice_read':
>> include/asm-generic/div64.h:222:35: warning: comparison of distinct pointer types lacks a cast
222 | (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
| ^~
kernel/trace/trace.c:8481:25: note: in expansion of macro 'do_div'
8481 | do_div(full, nr_pages);
| ^~~~~~
In file included from arch/mips/include/asm/bug.h:5,
from include/linux/bug.h:5,
from include/linux/mmdebug.h:5,
from include/linux/mm.h:6:
>> include/asm-generic/div64.h:234:32: warning: right shift count >= width of type [-Wshift-count-overflow]
234 | } else if (likely(((n) >> 32) == 0)) { \
| ^~
include/linux/compiler.h:76:45: note: in definition of macro 'likely'
76 | # define likely(x) __builtin_expect(!!(x), 1)
| ^
kernel/trace/trace.c:8481:25: note: in expansion of macro 'do_div'
8481 | do_div(full, nr_pages);
| ^~~~~~


vim +222 include/asm-generic/div64.h

^1da177e4c3f41 Linus Torvalds 2005-04-16 215
^1da177e4c3f41 Linus Torvalds 2005-04-16 216 /* The unnecessary pointer compare is there
^1da177e4c3f41 Linus Torvalds 2005-04-16 217 * to check for type safety (n must be 64bit)
^1da177e4c3f41 Linus Torvalds 2005-04-16 218 */
^1da177e4c3f41 Linus Torvalds 2005-04-16 219 # define do_div(n,base) ({ \
^1da177e4c3f41 Linus Torvalds 2005-04-16 220 uint32_t __base = (base); \
^1da177e4c3f41 Linus Torvalds 2005-04-16 221 uint32_t __rem; \
^1da177e4c3f41 Linus Torvalds 2005-04-16 @222 (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
911918aa7ef6f8 Nicolas Pitre 2015-11-02 223 if (__builtin_constant_p(__base) && \
911918aa7ef6f8 Nicolas Pitre 2015-11-02 224 is_power_of_2(__base)) { \
911918aa7ef6f8 Nicolas Pitre 2015-11-02 225 __rem = (n) & (__base - 1); \
911918aa7ef6f8 Nicolas Pitre 2015-11-02 226 (n) >>= ilog2(__base); \
c747ce4706190e Geert Uytterhoeven 2021-08-11 227 } else if (__builtin_constant_p(__base) && \
461a5e51060c93 Nicolas Pitre 2015-10-30 228 __base != 0) { \
461a5e51060c93 Nicolas Pitre 2015-10-30 229 uint32_t __res_lo, __n_lo = (n); \
461a5e51060c93 Nicolas Pitre 2015-10-30 230 (n) = __div64_const32(n, __base); \
461a5e51060c93 Nicolas Pitre 2015-10-30 231 /* the remainder can be computed with 32-bit regs */ \
461a5e51060c93 Nicolas Pitre 2015-10-30 232 __res_lo = (n); \
461a5e51060c93 Nicolas Pitre 2015-10-30 233 __rem = __n_lo - __res_lo * __base; \
911918aa7ef6f8 Nicolas Pitre 2015-11-02 @234 } else if (likely(((n) >> 32) == 0)) { \
^1da177e4c3f41 Linus Torvalds 2005-04-16 235 __rem = (uint32_t)(n) % __base; \
^1da177e4c3f41 Linus Torvalds 2005-04-16 236 (n) = (uint32_t)(n) / __base; \
c747ce4706190e Geert Uytterhoeven 2021-08-11 237 } else { \
^1da177e4c3f41 Linus Torvalds 2005-04-16 238 __rem = __div64_32(&(n), __base); \
c747ce4706190e Geert Uytterhoeven 2021-08-11 239 } \
^1da177e4c3f41 Linus Torvalds 2005-04-16 240 __rem; \
^1da177e4c3f41 Linus Torvalds 2005-04-16 241 })
^1da177e4c3f41 Linus Torvalds 2005-04-16 242

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