[bug report] ring-buffer: Validate boot range memory events

[Dan Carpenter <dan.carpenter@linaro.org>]

Hello Steven Rostedt (Google),

Commit 5f3b6e839f3c ("ring-buffer: Validate boot range memory
events") from Jun 12, 2024 (linux-next), leads to the following
Smatch static checker warning:

	kernel/trace/ring_buffer.c:1824 rb_meta_validate_events()
	error: uninitialized symbol 'head_page'.

kernel/trace/ring_buffer.c
    1751 static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
    1752 {
    1753         struct ring_buffer_meta *meta = cpu_buffer->ring_meta;
    1754         struct buffer_page *head_page;
    1755         unsigned long entry_bytes = 0;
    1756         unsigned long entries = 0;
    1757         int ret;
    1758         int i;
    1759 
    1760         if (!meta || !meta->head_buffer)
    1761                 return;
    1762 
    1763         /* Do the reader page first */
    1764         ret = rb_validate_buffer(cpu_buffer->reader_page->page, cpu_buffer->cpu);
    1765         if (ret < 0) {
    1766                 pr_info("Ring buffer reader page is invalid\n");
    1767                 goto invalid;

head_page is uninitialized

    1768         }
    1769         entries += ret;
    1770         entry_bytes += local_read(&cpu_buffer->reader_page->page->commit);
    1771         local_set(&cpu_buffer->reader_page->entries, ret);
    1772 
    1773         head_page = cpu_buffer->head_page;
    1774 
    1775         /* If both the head and commit are on the reader_page then we are done. */
    1776         if (head_page == cpu_buffer->reader_page &&
    1777             head_page == cpu_buffer->commit_page)
    1778                 goto done;
    1779 
    1780         /* Iterate until finding the commit page */
    1781         for (i = 0; i < meta->nr_subbufs + 1; i++, rb_inc_page(&head_page)) {
    1782 
    1783                 /* Reader page has already been done */
    1784                 if (head_page == cpu_buffer->reader_page)
    1785                         continue;
    1786 
    1787                 ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu);
    1788                 if (ret < 0) {
    1789                         pr_info("Ring buffer meta [%d] invalid buffer page\n",
    1790                                 cpu_buffer->cpu);
    1791                         goto invalid;
    1792                 }
    1793                 entries += ret;
    1794                 entry_bytes += local_read(&head_page->page->commit);
    1795                 local_set(&cpu_buffer->head_page->entries, ret);
    1796 
    1797                 if (head_page == cpu_buffer->commit_page)
    1798                         break;
    1799         }
    1800 
    1801         if (head_page != cpu_buffer->commit_page) {
    1802                 pr_info("Ring buffer meta [%d] commit page not found\n",
    1803                         cpu_buffer->cpu);
    1804                 goto invalid;
    1805         }
    1806  done:
    1807         local_set(&cpu_buffer->entries, entries);
    1808         local_set(&cpu_buffer->entries_bytes, entry_bytes);
    1809 
    1810         pr_info("Ring buffer meta [%d] is from previous boot!\n", cpu_buffer->cpu);
    1811         return;
    1812 
    1813  invalid:
    1814         /* The content of the buffers are invalid, reset the meta data */
    1815         meta->head_buffer = 0;
    1816         meta->commit_buffer = 0;
    1817 
    1818         /* Reset the reader page */
    1819         local_set(&cpu_buffer->reader_page->entries, 0);
    1820         local_set(&cpu_buffer->reader_page->page->commit, 0);
    1821 
    1822         /* Reset all the subbuffers */
    1823         for (i = 0; i < meta->nr_subbufs - 1; i++, rb_inc_page(&head_page)) {
--> 1824                 local_set(&head_page->entries, 0);
                                    ^^^^^^^^^
Uninitialized

    1825                 local_set(&head_page->page->commit, 0);
    1826         }
    1827 }

regards,
dan carpenter