Re: [PATCH v11 4/5] ring-buffer: Skip invalid sub-buffers when rewinding persistent ring buffer

[kernel test robot <lkp@intel.com>]

Hi Masami,

kernel test robot noticed the following build errors:

[auto build test ERROR on trace/for-next]
[also build test ERROR on geert-m68k/for-next geert-m68k/for-linus openrisc/for-next deller-parisc/for-next powerpc/next powerpc/fixes s390/features uml/next tip/x86/core linus/master uml/fixes v7.0-rc4 next-20260320]
[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/ring-buffer-Fix-to-update-per-subbuf-entries-of-persistent-ring-buffer/20260322-122412
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/177391156211.193994.7531495945584650297.stgit%40mhiramat.tok.corp.google.com
patch subject: [PATCH v11 4/5] ring-buffer: Skip invalid sub-buffers when rewinding persistent ring buffer
config: arc-defconfig (https://download.01.org/0day-ci/archive/20260322/202603221806.j3AZggGX-lkp@intel.com/config)
compiler: arc-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260322/202603221806.j3AZggGX-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202603221806.j3AZggGX-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from ./arch/arc/include/generated/asm/local.h:1,
                    from include/linux/ring_buffer_types.h:5,
                    from kernel/trace/ring_buffer.c:7:
   kernel/trace/ring_buffer.c: In function 'rb_meta_validate_events':
>> kernel/trace/ring_buffer.c:1965:36: error: 'bpage' undeclared (first use in this function); did you mean 'page'?
    1965 |                         local_set(&bpage->entries, 0);
         |                                    ^~~~~
   include/asm-generic/local.h:30:44: note: in definition of macro 'local_set'
      30 | #define local_set(l,i)  atomic_long_set((&(l)->a),(i))
         |                                            ^
   kernel/trace/ring_buffer.c:1965:36: note: each undeclared identifier is reported only once for each function it appears in
    1965 |                         local_set(&bpage->entries, 0);
         |                                    ^~~~~
   include/asm-generic/local.h:30:44: note: in definition of macro 'local_set'
      30 | #define local_set(l,i)  atomic_long_set((&(l)->a),(i))
         |                                            ^


vim +1965 kernel/trace/ring_buffer.c

  1910	
  1911	/* If the meta data has been validated, now validate the events */
  1912	static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
  1913	{
  1914		struct ring_buffer_cpu_meta *meta = cpu_buffer->ring_meta;
  1915		struct buffer_page *head_page, *orig_head;
  1916		unsigned long entry_bytes = 0;
  1917		unsigned long entries = 0;
  1918		int discarded = 0;
  1919		int ret;
  1920		u64 ts;
  1921		int i;
  1922	
  1923		if (!meta || !meta->head_buffer)
  1924			return;
  1925	
  1926		orig_head = head_page = cpu_buffer->head_page;
  1927	
  1928		/* Do the reader page first */
  1929		ret = rb_validate_buffer(cpu_buffer->reader_page, cpu_buffer->cpu, meta);
  1930		if (ret < 0) {
  1931			pr_info("Ring buffer meta [%d] invalid reader page detected\n",
  1932				cpu_buffer->cpu);
  1933			discarded++;
  1934		} else {
  1935			entries += ret;
  1936			entry_bytes += rb_page_size(cpu_buffer->reader_page);
  1937		}
  1938	
  1939		ts = head_page->page->time_stamp;
  1940	
  1941		/*
  1942		 * Try to rewind the head so that we can read the pages which already
  1943		 * read in the previous boot.
  1944		 */
  1945		if (head_page == cpu_buffer->tail_page)
  1946			goto skip_rewind;
  1947	
  1948		rb_dec_page(&head_page);
  1949		for (i = 0; i < meta->nr_subbufs + 1; i++, rb_dec_page(&head_page)) {
  1950	
  1951			/* Rewind until tail (writer) page. */
  1952			if (head_page == cpu_buffer->tail_page)
  1953				break;
  1954	
  1955			/* Rewind until unused page (no timestamp, no commit). */
  1956			if (!head_page->page->time_stamp && rb_page_commit(head_page) == 0)
  1957				break;
  1958	
  1959			/*
  1960			 * Skip if the page is invalid, or its timestamp is newer than the
  1961			 * previous valid page.
  1962			 */
  1963			ret = rb_validate_buffer(head_page, cpu_buffer->cpu, meta);
  1964			if (ret >= 0 && ts < head_page->page->time_stamp) {
> 1965				local_set(&bpage->entries, 0);
  1966				local_set(&bpage->page->commit, 0);
  1967				head_page->page->time_stamp = ts;
  1968				ret = -1;
  1969			}
  1970			if (ret < 0) {
  1971				if (!discarded)
  1972					pr_info("Ring buffer meta [%d] invalid buffer page detected\n",
  1973						cpu_buffer->cpu);
  1974				discarded++;
  1975			} else {
  1976				entries += ret;
  1977				entry_bytes += rb_page_size(head_page);
  1978				if (ret > 0)
  1979					local_inc(&cpu_buffer->pages_touched);
  1980				ts = head_page->page->time_stamp;
  1981			}
  1982		}
  1983		if (i)
  1984			pr_info("Ring buffer [%d] rewound %d pages\n", cpu_buffer->cpu, i);
  1985	
  1986		/* The last rewound page must be skipped. */
  1987		if (head_page != orig_head)
  1988			rb_inc_page(&head_page);
  1989	
  1990		/*
  1991		 * If the ring buffer was rewound, then inject the reader page
  1992		 * into the location just before the original head page.
  1993		 */
  1994		if (head_page != orig_head) {
  1995			struct buffer_page *bpage = orig_head;
  1996	
  1997			rb_dec_page(&bpage);
  1998			/*
  1999			 * Insert the reader_page before the original head page.
  2000			 * Since the list encode RB_PAGE flags, general list
  2001			 * operations should be avoided.
  2002			 */
  2003			cpu_buffer->reader_page->list.next = &orig_head->list;
  2004			cpu_buffer->reader_page->list.prev = orig_head->list.prev;
  2005			orig_head->list.prev = &cpu_buffer->reader_page->list;
  2006			bpage->list.next = &cpu_buffer->reader_page->list;
  2007	
  2008			/* Make the head_page the reader page */
  2009			cpu_buffer->reader_page = head_page;
  2010			bpage = head_page;
  2011			rb_inc_page(&head_page);
  2012			head_page->list.prev = bpage->list.prev;
  2013			rb_dec_page(&bpage);
  2014			bpage->list.next = &head_page->list;
  2015			rb_set_list_to_head(&bpage->list);
  2016			cpu_buffer->pages = &head_page->list;
  2017	
  2018			cpu_buffer->head_page = head_page;
  2019			meta->head_buffer = (unsigned long)head_page->page;
  2020	
  2021			/* Reset all the indexes */
  2022			bpage = cpu_buffer->reader_page;
  2023			meta->buffers[0] = rb_meta_subbuf_idx(meta, bpage->page);
  2024			bpage->id = 0;
  2025	
  2026			for (i = 1, bpage = head_page; i < meta->nr_subbufs;
  2027			     i++, rb_inc_page(&bpage)) {
  2028				meta->buffers[i] = rb_meta_subbuf_idx(meta, bpage->page);
  2029				bpage->id = i;
  2030			}
  2031	
  2032			/* We'll restart verifying from orig_head */
  2033			head_page = orig_head;
  2034		}
  2035	
  2036	 skip_rewind:
  2037		/* If the commit_buffer is the reader page, update the commit page */
  2038		if (meta->commit_buffer == (unsigned long)cpu_buffer->reader_page->page) {
  2039			cpu_buffer->commit_page = cpu_buffer->reader_page;
  2040			/* Nothing more to do, the only page is the reader page */
  2041			goto done;
  2042		}
  2043	
  2044		/* Iterate until finding the commit page */
  2045		for (i = 0; i < meta->nr_subbufs + 1; i++, rb_inc_page(&head_page)) {
  2046	
  2047			/* Reader page has already been done */
  2048			if (head_page == cpu_buffer->reader_page)
  2049				continue;
  2050	
  2051			ret = rb_validate_buffer(head_page, cpu_buffer->cpu, meta);
  2052			if (ret < 0) {
  2053				if (!discarded)
  2054					pr_info("Ring buffer meta [%d] invalid buffer page detected\n",
  2055						cpu_buffer->cpu);
  2056				discarded++;
  2057			} else {
  2058				/* If the buffer has content, update pages_touched */
  2059				if (ret)
  2060					local_inc(&cpu_buffer->pages_touched);
  2061	
  2062				entries += ret;
  2063				entry_bytes += rb_page_size(head_page);
  2064			}
  2065			if (head_page == cpu_buffer->commit_page)
  2066				break;
  2067		}
  2068	
  2069		if (head_page != cpu_buffer->commit_page) {
  2070			pr_info("Ring buffer meta [%d] commit page not found\n",
  2071				cpu_buffer->cpu);
  2072			goto invalid;
  2073		}
  2074	 done:
  2075		local_set(&cpu_buffer->entries, entries);
  2076		local_set(&cpu_buffer->entries_bytes, entry_bytes);
  2077	
  2078		pr_info("Ring buffer meta [%d] is from previous boot! (%d pages discarded)\n",
  2079			cpu_buffer->cpu, discarded);
  2080		return;
  2081	
  2082	 invalid:
  2083		/* The content of the buffers are invalid, reset the meta data */
  2084		meta->head_buffer = 0;
  2085		meta->commit_buffer = 0;
  2086	
  2087		/* Reset the reader page */
  2088		local_set(&cpu_buffer->reader_page->entries, 0);
  2089		local_set(&cpu_buffer->reader_page->page->commit, 0);
  2090	
  2091		/* Reset all the subbuffers */
  2092		for (i = 0; i < meta->nr_subbufs - 1; i++, rb_inc_page(&head_page)) {
  2093			local_set(&head_page->entries, 0);
  2094			rb_init_page(head_page->page);
  2095		}
  2096	}
  2097	

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