On Fri, 2012-11-30 at 11:12 -0500, Steven Rostedt wrote: > From: Steven Rostedt <[email protected]> > > The function rb_check_pages() was added to make sure the ring buffer's > pages were sane. This check is done when the ring buffer size is modified > as well as when the iterator is released (closing the "trace" file), > as that was considered a non fast path and a good place to do a sanity > check. > > The problem is that the check does not have any locks around it. > If one process were to read the trace file, and another were to read > the raw binary file, the check could happen while the reader is reading > the file. > > The issues with this is that the check requires to clear the HEAD page > before doing the full check and it restores it afterward. But readers > require the HEAD page to exist before it can read the buffer, otherwise > it gives a nasty warning and disables the buffer. > > By adding the reader lock around the check, this keeps the race from > happening. > > Cc: [email protected] # 3.6
Again, quilt failed to Cc stable :-( -- Steve > Signed-off-by: Steven Rostedt <[email protected]> > --- > kernel/trace/ring_buffer.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index ec01803..4cb5e51 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -3783,12 +3783,17 @@ void > ring_buffer_read_finish(struct ring_buffer_iter *iter) > { > struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer; > + unsigned long flags; > > /* > * Ring buffer is disabled from recording, here's a good place > - * to check the integrity of the ring buffer. > + * to check the integrity of the ring buffer. > + * Must prevent readers from trying to read, as the check > + * clears the HEAD page and readers require it. > */ > + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); > rb_check_pages(cpu_buffer); > + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); > > atomic_dec(&cpu_buffer->record_disabled); > atomic_dec(&cpu_buffer->buffer->resize_disabled); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
