* Re: [PATCH v11 4/5] ring-buffer: Skip invalid sub-buffers when rewinding persistent ring buffer
2026-03-22 23:18 ` [PATCH v11 4/5] ring-buffer: Skip invalid sub-buffers when rewinding persistent ring buffer kernel test robot
@ 2026-03-23 11:50 ` Masami Hiramatsu
0 siblings, 0 replies; 2+ messages in thread
From: Masami Hiramatsu @ 2026-03-23 11:50 UTC (permalink / raw)
To: kernel test robot
Cc: Steven Rostedt, llvm, oe-kbuild-all, Mathieu Desnoyers,
linux-kernel, linux-trace-kernel, Ian Rogers
On Mon, 23 Mar 2026 07:18:07 +0800
kernel test robot <lkp@intel.com> wrote:
> 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 uml/fixes v7.0-rc4 next-20260320]
> [cannot apply to linus/master]
> [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: x86_64-kexec (https://download.01.org/0day-ci/archive/20260323/202603230725.uMAZiKJx-lkp@intel.com/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260323/202603230725.uMAZiKJx-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/202603230725.uMAZiKJx-lkp@intel.com/
>
> All errors (new ones prefixed by >>):
>
> >> kernel/trace/ring_buffer.c:1965:15: error: use of undeclared identifier 'bpage'
> 1965 | local_set(&bpage->entries, 0);
> | ^
> kernel/trace/ring_buffer.c:1966:15: error: use of undeclared identifier 'bpage'
> 1966 | local_set(&bpage->page->commit, 0);
> | ^
> 2 errors generated.
>
>
> vim +/bpage +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);
Ooops, sorry, I made a copy & paste mistake. this should be head_page->entries and head_page->page_commit.
Let me send v12 on the latest tracing/fixes.
Thanks,
> 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
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
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