linux-kernel - Re: [patch] ftrace: clear bits properly in reset_iter

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Date:	Sat, 09 Jun 2012 12:57:56 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] ftrace: clear bits properly in reset_iter_read()

On Sat, 2012-06-09 at 19:10 +0300, Dan Carpenter wrote:
> There is a typo here where '&' is used instead of '|' and it turns the
> statement into a noop.  The original code is equivalent to:
> 
> 	iter->flags &= ~((1 << 2) & (1 << 4));
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
> This is a static checker fix and I'm not super familiar with ftrace.
> Please review carefully.
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index a008663..97da2dc 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2358,7 +2358,7 @@ static void reset_iter_read(struct ftrace_iterator *iter)
>  {
>  	iter->pos = 0;
>  	iter->func_pos = 0;
> -	iter->flags &= ~(FTRACE_ITER_PRINTALL & FTRACE_ITER_HASH);
> +	iter->flags &= ~(FTRACE_ITER_PRINTALL | FTRACE_ITER_HASH);

Thanks! This is a real minor bug, but as it is a simple fix I will
probably queue it up for 3.5 and stable. The reason that it has gone
unnoticed for so long is that this would only show up if you did a lseek
on the function list file. Which is not a common operation to do.

I checked the code and if someone were to do an lseek with these flags
set then they would just get the hash list again (and not the function
list). It's a bug, yes, but not a big one.

I'll queue it up on Monday.

-- Steve


>  }
>  
>  static void *t_start(struct seq_file *m, loff_t *pos)


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