On Wed, Sep 07, 2022 at 04:13:58PM +0800, lijiazi wrote:
> >
> > Ah, it's not an issue with the commit value but the write value.
> >
> > Can you test this patch.
> >
> > -- Steve
> >
> > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> > index d59b6a328b7f..6bf7706bb33b 100644
> > --- a/kernel/trace/ring_buffer.c
> > +++ b/kernel/trace/ring_buffer.c
> > @@ -2608,6 +2608,9 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
> > /* Mark the rest of the page with padding */
> > rb_event_set_padding(event);
> >
> > + /* Make sure the padding is visible before the write update */
> > + smp_wmb();
> > +
>
> I checked several ramdumps, most of the padding event that caused crash not be
> written here. Because its corresponding ring_buffer_event->time_delta is
> not 0, take one of them as an example:
> crash> struct ring_buffer_event ffffffd10b553fe4
> struct ring_buffer_event {
> type_len = 29,
> time_delta = 1,
> array = 0xffffffd10b553fe8
> }
> and array[0] is 0x18:
> crash> rd ffffffd10b553fe8
> ffffffd10b553fe8: 0000000500000018 ........
> 0x18 = 0xff0 - 0xfd4 - 0x4
> 0xfd4 is end address of last data event in reader page.
>
> The available space size is 0x18 bytes, and next event want to write is
> signal_deliver, this event need 0x28 bytes:
> crash> trace_event_raw_signal_deliver -x
> struct trace_event_raw_signal_deliver {
> struct trace_entry ent;
> int sig;
> int errno;
> int code;
> unsigned long sa_handler;
> unsigned long sa_flags;
> char __data[0];
> }
> SIZE: 0x28
> So trigger rb move tail, tail value in rb_reset_tail is 0xfd4, the
> following if condition is false:
> if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE))
> > /* Set the write back to the previous setting */
> > local_sub(length, &tail_page->write);
> > return;
> > @@ -4580,6 +4583,13 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
> > goto again;
> >
> > out:
> > + /* If the write is past the end of page, a writer is still updating it */
> > + if (reader && reader->write > BUF_PAGE_SIZE)
Maybe should use rb_page_write(reeader) to filter out RB_WRITE_INTCNT?
Thanks!
> > + reader = NULL;
> > +
> > + /* Make sure we see any padding after the write update */
> > + smp_rmb();
> > +
> > /* Update the read_stamp on the first event */
> > if (reader && reader->read == 0)
> > cpu_buffer->read_stamp = reader->page->time_stamp;
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