linux-kernel - RE: [PATCH] fork: Improve error message for corrupted page tables

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Date:   Fri, 2 Aug 2019 06:52:10 +0000
From:   "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: RE: [PATCH] fork: Improve error message for corrupted page tables

> >
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Suggested-by/Acked-by: Dave Hansen <dave.hansen@...el.com>
> 
> Though I am not sure, should the above be two separate lines instead ?

Sure! Will split them in V2.

> 
> > Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
> > ---
> >  include/linux/mm_types_task.h | 7 +++++++
> >  kernel/fork.c                 | 4 ++--
> >  2 files changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/mm_types_task.h
> > b/include/linux/mm_types_task.h index d7016dcb245e..881f4ea3a1b5
> > 100644
> > --- a/include/linux/mm_types_task.h
> > +++ b/include/linux/mm_types_task.h
> > @@ -44,6 +44,13 @@ enum {
> >  	NR_MM_COUNTERS
> >  };
> >
> > +static const char * const resident_page_types[NR_MM_COUNTERS] = {
> > +	"MM_FILEPAGES",
> > +	"MM_ANONPAGES",
> > +	"MM_SWAPENTS",
> > +	"MM_SHMEMPAGES",
> > +};
> 
> Should index them to match respective typo macros.
> 
> 	[MM_FILEPAGES] = "MM_FILEPAGES",
> 	[MM_ANONPAGES] = "MM_ANONPAGES",
> 	[MM_SWAPENTS] = "MM_SWAPENTS",
> 	[MM_SHMEMPAGES] = "MM_SHMEMPAGES",

Sure! Will change it.

> > +
> >  #if USE_SPLIT_PTE_PTLOCKS && defined(CONFIG_MMU)  #define
> > SPLIT_RSS_COUNTING
> >  /* per-thread cached information, */
> > diff --git a/kernel/fork.c b/kernel/fork.c index
> > 2852d0e76ea3..6aef5842d4e0 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -649,8 +649,8 @@ static void check_mm(struct mm_struct *mm)
> >  		long x = atomic_long_read(&mm->rss_stat.count[i]);
> >
> >  		if (unlikely(x))
> > -			printk(KERN_ALERT "BUG: Bad rss-counter state "
> > -					  "mm:%p idx:%d val:%ld\n", mm, i, x);
> > +			pr_alert("BUG: Bad rss-counter state mm:%p type:%s
> val:%ld\n",
> > +				 mm, resident_page_types[i], x);
> It changes the print function as well, though very minor change but perhaps
> mention that in the commit message ?

Sure! Will mention it in V2.
I have changed printk() to pr_alert() because the other message in check_mm() uses pr_alert().

Regards,
Sai