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tracing: Ensure trace buffer is at least 4096 bytes large

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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.

Link: https://lkml.kernel.org/r/20220214134456.1751749-1-svens@linux.ibm.com

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Sven Schnelle 2022-02-14 14:44:56 +01:00 committed by Steven Rostedt (Google)
parent bc82c38a69
commit 7acf3a127b
1 changed files with 6 additions and 4 deletions
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10
kernel/trace/trace.c
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@ -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);