2022-02-14 19:25:30

by Sven Schnelle

Subject: [PATCH] ftrace: ensure trace buffer is at least 4096 bytes large

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 <[email protected]>
---
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);
--
2.32.0

2022-02-14 21:23:09

by Steven Rostedt

Subject: Re: [PATCH] ftrace: ensure trace buffer is at least 4096 bytes large

On Mon, 14 Feb 2022 14:44:56 +0100
Sven Schnelle <[email protected]> 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 <[email protected]>

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);