linux-kernel - Re: [RFA][PATCH 1/5] ftrace/x86: Run a sync after fixup on failure

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Date:	Thu, 27 Feb 2014 16:58:12 +0100
From:	Petr Mládek <pmladek@...e.cz>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"H. Peter Anvin" <hpa@...or.com>, stable@...r.kernel.org
Subject: Re: [RFA][PATCH 1/5] ftrace/x86: Run a sync after fixup on failure

On Thu 27-02-14 10:46:17, Steven Rostedt wrote:
> [Request for Ack]
> 
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> 
> If a failure occurs while enabling a trace, it bails out and will remove
> the tracepoints to be back to what the code originally was. But the fix
> up had some bugs in it. By injecting a failure in the code, the fix up
> ran to completion, but shortly afterward the system rebooted.
> 
> There was two bugs here.
> 
> The first was that there was no final sync run across the CPUs after the
> fix up was done, and before the ftrace int3 handler flag was reset. That
> means that other CPUs could still see the breakpoint and trigger on it
> long after the flag was cleared, and the int3 handler would think it was
> a spurious interrupt. Worse yet, the int3 handler could hit other breakpoints
> because the ftrace int3 handler flag would have prevented the int3 handler
> from going further.
> 
> The second bug was that the removal of the breakpoints required the
> "within()" logic updates instead of accessing the ip address directly.
> 
> Link: http://lkml.kernel.org/r/1392650573-3390-1-git-send-email-pmladek@suse.cz
> 
> Reported-by: Petr Mladek <pmladek@...e.cz>

Tested-by: Petr Mladek <pmladek@...e.cz>

> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: stable@...r.kernel.org # 3.5+
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  arch/x86/kernel/ftrace.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index e625319..6b566c8 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -455,7 +455,7 @@ static int remove_breakpoint(struct dyn_ftrace *rec)
>  	}
>  
>   update:
> -	return probe_kernel_write((void *)ip, &nop[0], 1);
> +	return ftrace_write(ip, nop, 1);
>  }
>  
>  static int add_update_code(unsigned long ip, unsigned const char *new)
> @@ -634,6 +634,7 @@ void ftrace_replace_code(int enable)
>  		rec = ftrace_rec_iter_record(iter);
>  		remove_breakpoint(rec);
>  	}
> +	run_sync();
>  }
>  
>  static int
> @@ -664,7 +665,7 @@ ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
>  	return ret;
>  
>   fail_update:
> -	probe_kernel_write((void *)ip, &old_code[0], 1);
> +	ftrace_write(ip, old_code, 1);
>  	goto out;
>  }
>  
> -- 
> 1.8.5.3
> 
> 
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