Messages in this thread | | | Date | Mon, 14 Feb 2022 13:42:38 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] ftrace: ensure trace buffer is at least 4096 bytes large |
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On Mon, 14 Feb 2022 14:44:56 +0100 Sven Schnelle <svens@linux.ibm.com> wrote:
> Booting the kernel with 'trace_buf_size=1' give a warning at > boot during the ftrace selftests: > > [ 0.892809] Running postponed tracer tests: > [ 0.892893] Testing tracer function: > [ 0.901899] Callback from call_rcu_tasks_trace() invoked. > [ 0.983829] Callback from call_rcu_tasks_rude() invoked. > [ 1.072003] .. bad ring buffer .. corrupted trace buffer .. > [ 1.091944] Callback from call_rcu_tasks() invoked. > [ 1.097695] PASSED > [ 1.097701] Testing dynamic ftrace: .. filter failed count=0 ..FAILED! > [ 1.353474] ------------[ cut here ]------------ > [ 1.353478] WARNING: CPU: 0 PID: 1 at kernel/trace/trace.c:1951 run_tracer_selftest+0x13c/0x1b0 > > Therefore enforce a minimum of 4096 bytes to make the selftest pass. > > Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Thanks,
I'll queue this up for the next merge window.
-- Steve
> --- > kernel/trace/trace.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 7c2578efde26..3050892d1812 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -1474,10 +1474,12 @@ static int __init set_buf_size(char *str) > if (!str) > return 0; > buf_size = memparse(str, &str); > - /* nr_entries can not be zero */ > - if (buf_size == 0) > - return 0; > - trace_buf_size = buf_size; > + /* > + * nr_entries can not be zero and the startup > + * tests require some buffer space. Therefore > + * ensure we have at least 4096 bytes of buffer. > + */ > + trace_buf_size = max(4096UL, buf_size); > return 1; > } > __setup("trace_buf_size=", set_buf_size);
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