linux-kernel - Re: [PATCH 5/8] ring-buffer: Add ring_buffer

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Date: Fri, 8 Mar 2024 18:42:51 +0800
From: kernel test robot <lkp@...el.com>
To: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Cc: oe-kbuild-all@...ts.linux.dev, Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Vincent Donnefort <vdonnefort@...gle.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, suleiman@...gle.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Vineeth Pillai <vineeth@...byteword.org>,
	Youssef Esmat <youssefesmat@...gle.com>,
	Beau Belgrave <beaub@...ux.microsoft.com>,
	Alexander Graf <graf@...zon.com>, Baoquan He <bhe@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 5/8] ring-buffer: Add ring_buffer_meta data

Hi Steven,

kernel test robot noticed the following build warnings:

[auto build test WARNING on next-20240305]
[cannot apply to tip/x86/core akpm-mm/mm-everything linus/master v6.8-rc7 v6.8-rc6 v6.8-rc5 v6.8-rc7]
[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/Steven-Rostedt/ring-buffer-Allow-mapped-field-to-be-set-without-mapping/20240306-100047
base:   next-20240305
patch link:    https://lore.kernel.org/r/20240306020006.100449500%40goodmis.org
patch subject: [PATCH 5/8] ring-buffer: Add ring_buffer_meta data
config: sh-defconfig (https://download.01.org/0day-ci/archive/20240308/202403081831.EWSQPo2a-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240308/202403081831.EWSQPo2a-lkp@intel.com/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@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202403081831.EWSQPo2a-lkp@intel.com/

All warnings (new ones prefixed by >>):

   kernel/trace/ring_buffer.c: In function 'rb_set_commit_to_write':
>> kernel/trace/ring_buffer.c:3224:45: warning: assignment to 'long unsigned int' from 'struct buffer_data_page *' makes integer from pointer without a cast [-Wint-conversion]
    3224 |                         meta->commit_buffer = cpu_buffer->commit_page->page;
         |                                             ^


vim +3224 kernel/trace/ring_buffer.c

  3192	
  3193	static __always_inline void
  3194	rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
  3195	{
  3196		unsigned long max_count;
  3197	
  3198		/*
  3199		 * We only race with interrupts and NMIs on this CPU.
  3200		 * If we own the commit event, then we can commit
  3201		 * all others that interrupted us, since the interruptions
  3202		 * are in stack format (they finish before they come
  3203		 * back to us). This allows us to do a simple loop to
  3204		 * assign the commit to the tail.
  3205		 */
  3206	 again:
  3207		max_count = cpu_buffer->nr_pages * 100;
  3208	
  3209		while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
  3210			if (RB_WARN_ON(cpu_buffer, !(--max_count)))
  3211				return;
  3212			if (RB_WARN_ON(cpu_buffer,
  3213				       rb_is_reader_page(cpu_buffer->tail_page)))
  3214				return;
  3215			/*
  3216			 * No need for a memory barrier here, as the update
  3217			 * of the tail_page did it for this page.
  3218			 */
  3219			local_set(&cpu_buffer->commit_page->page->commit,
  3220				  rb_page_write(cpu_buffer->commit_page));
  3221			rb_inc_page(&cpu_buffer->commit_page);
  3222			if (cpu_buffer->ring_meta) {
  3223				struct ring_buffer_meta *meta = cpu_buffer->ring_meta;
> 3224				meta->commit_buffer = cpu_buffer->commit_page->page;
  3225			}
  3226			/* add barrier to keep gcc from optimizing too much */
  3227			barrier();
  3228		}
  3229		while (rb_commit_index(cpu_buffer) !=
  3230		       rb_page_write(cpu_buffer->commit_page)) {
  3231	
  3232			/* Make sure the readers see the content of what is committed. */
  3233			smp_wmb();
  3234			local_set(&cpu_buffer->commit_page->page->commit,
  3235				  rb_page_write(cpu_buffer->commit_page));
  3236			RB_WARN_ON(cpu_buffer,
  3237				   local_read(&cpu_buffer->commit_page->page->commit) &
  3238				   ~RB_WRITE_MASK);
  3239			barrier();
  3240		}
  3241	
  3242		/* again, keep gcc from optimizing */
  3243		barrier();
  3244	
  3245		/*
  3246		 * If an interrupt came in just after the first while loop
  3247		 * and pushed the tail page forward, we will be left with
  3248		 * a dangling commit that will never go forward.
  3249		 */
  3250		if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
  3251			goto again;
  3252	}
  3253	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki