On Fri, 6 Mar 2026 09:59:35 -0500 Steven Rostedt <[email protected]> wrote:
> On Fri, 6 Mar 2026 17:46:09 +0900 > Masami Hiramatsu (Google) <[email protected]> wrote: > > > On Thu, 5 Mar 2026 13:03:48 -0500 > > Steven Rostedt <[email protected]> wrote: > > > > > On Thu, 26 Feb 2026 22:38:43 +0900 > > > "Masami Hiramatsu (Google)" <[email protected]> wrote: > > > > > > > From: Masami Hiramatsu (Google) <[email protected]> > > > > > > > > Since the MSBs of rb_data_page::commit are used for storing > > > > RB_MISSED_EVENTS and RB_MISSED_STORED, we need to mask out those bits > > > > when it is used for finding the size of data pages. > > > > > > > > Fixes: 5f3b6e839f3c ("ring-buffer: Validate boot range memory events") > > > > Fixes: 5b7be9c709e1 ("ring-buffer: Add test to validate the time stamp > > > > deltas") > > > > Cc: [email protected] > > > > > > This is unneeded for the current way things work. > > > > > > The missed events flags are added when a page is read, so the commits in > > > the write buffer should never have those flags set. If they did, the ring > > > buffer code itself would break. > > > > Hmm, but commit ca296d32ece3 ("tracing: ring_buffer: Rewind persistent > > ring buffer on reboot") may change it. Maybe we should treat it while > > unwinding it? > > Might change what? So the above commit removes clearing (resetting) meta->commit after read the page (thus the missed events flags will be there). But those pages will be recovered (rewound) after reboot. Thus the validation runs on those pages (and detect invalid pages) > > > > > > > > > But as patch 3 is adding a flag, you should likely merge this and patch 3 > > > together, as the only way that flag would get set is if the validator set > > > it on a previous boot. And then this would be needed for subsequent boots > > > that did not reset the buffer. > > > > It is OK to combine these 2 patches. But my question is that when the flag > > must be checked and when it must be ignored. Since the flags are encoded > > to commit, if that is used for limiting or indexing inside the page, > > we must mask the flag or check the max size to avoid accessing outside of > > the subpage. > > > > > > > > Hmm, I don't think we even need to do that! Because if it is set, it would > > > simply warn again that a page is invalid, and I think we *want* that! As > > > it > > > would preserve that pages were invalid and not be cleared with a simple > > > reboot. > > > > OK, then I don't mark it, but just invalidate the subpage. > > No, I mean you can mark it, but then just have the validator skip it. > Something like: This may not work because RB_MISSED_EVENTS are added, instead of set. So the commit will be `original_commit + RB_MISSED_EVENTS`. Anyway, in v8, any of invalid (out of range) commit value is treated as corrupted in rb_validate_buffer(). Thanks, > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 156ed19fb569..c98ab86cf384 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -1950,6 +1951,10 @@ static void rb_meta_validate_events(struct > ring_buffer_per_cpu *cpu_buffer) > rb_dec_page(&head_page); > for (i = 0; i < meta->nr_subbufs + 1; i++, rb_dec_page(&head_page)) { > > + /* Skip if this buffer was flagged as bad before */ > + if (local_read(&head_page->page->commit) == RB_MISSED_EVENTS) > + continue; > + > /* Rewind until tail (writer) page. */ > if (head_page == cpu_buffer->tail_page) > break; > -- Masami Hiramatsu (Google) <[email protected]>
