linux-kernel - Re: [PATCH 1/2] memory-failure: Send right signal code to correct thread

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Message-ID: <20140523033438.GC16945@gchen.bj.intel.com>
Date:	Thu, 22 May 2014 23:34:38 -0400
From:	"Chen, Gong" <gong.chen@...ux.intel.com>
To:	Tony Luck <tony.luck@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andi Kleen <andi@...stfloor.org>, Borislav Petkov <bp@...e.de>,
	Chen Gong <gong.chen@...ux.jf.intel.com>
Subject: Re: [PATCH 1/2] memory-failure: Send right signal code to correct
 thread

On Tue, May 20, 2014 at 09:28:00AM -0700, Luck, Tony wrote:
> When a thread in a multi-threaded application hits a machine
> check because of an uncorrectable error in memory - we want to
> send the SIGBUS with si.si_code = BUS_MCEERR_AR to that thread.
> Currently we fail to do that if the active thread is not the
> primary thread in the process. collect_procs() just finds primary
> threads and this test:
> 	if ((flags & MF_ACTION_REQUIRED) && t == current) {
> will see that the thread we found isn't the current thread
> and so send a si.si_code = BUS_MCEERR_AO to the primary
> (and nothing to the active thread at this time).
> 
> We can fix this by checking whether "current" shares the same
> mm with the process that collect_procs() said owned the page.
> If so, we send the SIGBUS to current (with code BUS_MCEERR_AR).
> 
> Reported-by: Otto Bruggeman <otto.g.bruggeman@...el.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  mm/memory-failure.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 35ef28acf137..642c8434b166 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -204,9 +204,9 @@ static int kill_proc(struct task_struct *t, unsigned long addr, int trapno,
>  #endif
>  	si.si_addr_lsb = compound_order(compound_head(page)) + PAGE_SHIFT;
>  
> -	if ((flags & MF_ACTION_REQUIRED) && t == current) {
> +	if ((flags & MF_ACTION_REQUIRED) && t->mm == current->mm) {
>  		si.si_code = BUS_MCEERR_AR;
> -		ret = force_sig_info(SIGBUS, &si, t);
> +		ret = force_sig_info(SIGBUS, &si, current);
>  	} else {
>  		/*
>  		 * Don't use force here, it's convenient if the signal
> -- 
> 1.8.4.1
Very interesting. I remembered there was a thread about AO error. Here is
the link: http://www.spinics.net/lists/linux-mm/msg66653.html.
According to this link, I have two concerns:

1) how to handle the similar scenario like it in this link. I mean once
the main thread doesn't handle AR error but a thread does this, if SIGBUS
can't be handled at once.
2) why that patch isn't merged. From that thread, Naoya should mean
"acknowledge" :-).

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