linux-kernel - Re: [PATCH] mm, memory-failure: clarify error message

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Message-ID: <20190520102106.GA12721@hori.linux.bs1.fc.nec.co.jp>
Date:   Mon, 20 May 2019 10:21:05 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
CC:     Jane Chu <jane.chu@...cle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH] mm, memory-failure: clarify error message

On Fri, May 17, 2019 at 10:18:02AM +0530, Anshuman Khandual wrote:
> 
> 
> On 05/17/2019 09:38 AM, Jane Chu wrote:
> > Some user who install SIGBUS handler that does longjmp out
> 
> What the longjmp about ? Are you referring to the mechanism of catching the
> signal which was registered ?

AFAIK, longjmp() might be useful for signal-based retrying, so highly
optimized applications like Oracle DB might want to utilize it to handle
memory errors in application level, I guess.

> 
> > therefore keeping the process alive is confused by the error
> > message
> >   "[188988.765862] Memory failure: 0x1840200: Killing
> >    cellsrv:33395 due to hardware memory corruption"
> 
> Its a valid point because those are two distinct actions.
> 
> > Slightly modify the error message to improve clarity.
> > 
> > Signed-off-by: Jane Chu <jane.chu@...cle.com>
> > ---
> >  mm/memory-failure.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index fc8b517..14de5e2 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -216,10 +216,9 @@ static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)
> >  	short addr_lsb = tk->size_shift;
> >  	int ret;
> >  
> > -	pr_err("Memory failure: %#lx: Killing %s:%d due to hardware memory corruption\n",
> > -		pfn, t->comm, t->pid);
> > -
> >  	if ((flags & MF_ACTION_REQUIRED) && t->mm == current->mm) {
> > +		pr_err("Memory failure: %#lx: Killing %s:%d due to hardware memory "
> > +			"corruption\n", pfn, t->comm, t->pid);
> >  		ret = force_sig_mceerr(BUS_MCEERR_AR, (void __user *)tk->addr,
> >  				       addr_lsb, current);
> >  	} else {
> > @@ -229,6 +228,8 @@ static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)
> >  		 * This could cause a loop when the user sets SIGBUS
> >  		 * to SIG_IGN, but hopefully no one will do that?
> >  		 */
> > +		pr_err("Memory failure: %#lx: Sending SIGBUS to %s:%d due to hardware "
> > +			"memory corruption\n", pfn, t->comm, t->pid);
> >  		ret = send_sig_mceerr(BUS_MCEERR_AO, (void __user *)tk->addr,
> >  				      addr_lsb, t);  /* synchronous? */
> 
> As both the pr_err() messages are very similar, could not we just switch between "Killing"
> and "Sending SIGBUS to" based on a variable e.g action_[kill|sigbus] evaluated previously
> with ((flags & MF_ACTION_REQUIRED) && t->mm == current->mm).

That might need additional if sentence, which I'm not sure worth doing.
I think that the simplest fix for the reported problem (a confusing message)
is like below:

	-	pr_err("Memory failure: %#lx: Killing %s:%d due to hardware memory corruption\n",
	+	pr_err("Memory failure: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
			pfn, t->comm, t->pid);

Or, if we have a good reason to separate the message for MF_ACTION_REQUIRED and
MF_ACTION_OPTIONAL, that might be OK.

Thanks,
Naoya Horiguchi