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SubjectRe: [PATCH 05/13] ftrace: Call trace_parser_clear() properly
Frederic Weisbecker wrote:
> On Tue, Dec 08, 2009 at 11:15:30AM +0800, Li Zefan wrote:
>> I found a weird behavior:
>>
>> # echo 'fuse:*' > set_ftrace_filter
>> bash: echo: write error: Invalid argument
>> # cat set_ftrace_filter
>> fuse_dev_fasync
>> fuse_dev_poll
>> fuse_copy_do
>>
>> We should call trace_parser_clear() no matter ftrace_process_regex()
>> returns 0 or -errno.
>>
>> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
>> ---
>> kernel/trace/ftrace.c | 3 +--
>> 1 files changed, 1 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>> index 08a3fb5..ff8aecd 100644
>> --- a/kernel/trace/ftrace.c
>> +++ b/kernel/trace/ftrace.c
>> @@ -2208,10 +2208,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
>> !trace_parser_cont(parser)) {
>> ret = ftrace_process_regex(parser->buffer,
>> parser->idx, enable);
>> + trace_parser_clear(parser);
>> if (ret)
>> goto out_unlock;
>> -
>> - trace_parser_clear(parser);
>> }
>
>
> I'm missing something. How that can happen. Anytime we reopen
> the file, the parser is re-allocated.
>

It happened at file closing..

static int
ftrace_regex_release(struct inode *inode, struct file *file, int enable)
{
...
parser = &iter->parser;
if (trace_parser_loaded(parser)) {
parser->buffer[parser->idx] = 0;
/* here ! */
ftrace_match_records(parser->buffer, parser->idx, enable);
}
...
}
> I guess that happens if you open in rw mode? But not using the
> example in the changelog?

I've confirmed that example I was using can reveal this bug.


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