4.14-stable review patch. If anyone has any objections, please let me know.
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From: Steven Rostedt (Google) rostedt@goodmis.org
commit 7be76461f302ec05cbd62b90b2a05c64299ca01f upstream.
It use to be that only the top level instance had a snapshot buffer (for latency tracers like wakeup and irqsoff). The update of the ring buffer size would check if the instance was the top level and if so, it would also update the snapshot buffer as it needs to be the same as the main buffer.
Now that lower level instances also has a snapshot buffer, they too need to update their snapshot buffer sizes when the main buffer is changed, otherwise the following can be triggered:
# cd /sys/kernel/tracing # echo 1500 > buffer_size_kb # mkdir instances/foo # echo irqsoff > instances/foo/current_tracer # echo 1000 > instances/foo/buffer_size_kb
Produces:
WARNING: CPU: 2 PID: 856 at kernel/trace/trace.c:1938 update_max_tr_single.part.0+0x27d/0x320
Which is:
ret = ring_buffer_swap_cpu(tr->max_buffer.buffer, tr->array_buffer.buffer, cpu);
if (ret == -EBUSY) { [..] }
WARN_ON_ONCE(ret && ret != -EAGAIN && ret != -EBUSY); <== here
That's because ring_buffer_swap_cpu() has:
int ret = -EINVAL;
[..]
/* At least make sure the two buffers are somewhat the same */ if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages) goto out;
[..] out: return ret; }
Instead, update all instances' snapshot buffer sizes when their main buffer size is updated.
Link: https://lkml.kernel.org/r/20231205220010.454662151@goodmis.org
Cc: stable@vger.kernel.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Andrew Morton akpm@linux-foundation.org Fixes: 6d9b3fa5e7f6 ("tracing: Move tracing_max_latency into trace_array") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/trace/trace.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5253,8 +5253,7 @@ static int __tracing_resize_ring_buffer( return ret;
#ifdef CONFIG_TRACER_MAX_TRACE - if (!(tr->flags & TRACE_ARRAY_FL_GLOBAL) || - !tr->current_trace->use_max_tr) + if (!tr->current_trace->use_max_tr) goto out;
ret = ring_buffer_resize(tr->max_buffer.buffer, size, cpu);