linux-kernel - Re: [PATCH v2] mm: kmemleak: Use mempool allocations for kmemleak objects

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Date:   Wed, 31 Jul 2019 10:54:03 -0400
From:   Qian Cai <cai@....pw>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2] mm: kmemleak: Use mempool allocations for kmemleak
 objects

On Wed, 2019-07-31 at 15:48 +0100, Catalin Marinas wrote:
> On Wed, Jul 31, 2019 at 08:02:30AM -0400, Qian Cai wrote:
> > On Jul 31, 2019, at 5:53 AM, Catalin Marinas <catalin.marinas@....com>
> > wrote:
> > > On Tue, Jul 30, 2019 at 04:22:37PM -0400, Qian Cai wrote:
> > > > On Tue, 2019-07-30 at 12:57 -0700, Andrew Morton wrote:
> > > > > On Sat, 27 Jul 2019 14:23:33 +0100 Catalin Marinas <catalin.marinas@ar
> > > > > m.com>
> > > > > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > > > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > > > > @@ -2011,6 +2011,12 @@
> > > > > >  			Built with
> > > > > > CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
> > > > > >  			the default is off.
> > > > > >  
> > > > > > +	kmemleak.mempool=
> > > > > > +			[KNL] Boot-time tuning of the minimum
> > > > > > kmemleak
> > > > > > +			metadata pool size.
> > > > > > +			Format: <int>
> > > > > > +			Default: NR_CPUS * 4
> > > > > > +
> > > > 
> > > > Catalin, BTW, it is right now unable to handle a large size. I tried to
> > > > reserve
> > > > 64M (kmemleak.mempool=67108864),
> 
> [...]
> > > It looks like the mempool cannot be created. 64M objects means a
> > > kmalloc(512MB) for the pool array in mempool_init_node(), so that hits
> > > the MAX_ORDER warning in __alloc_pages_nodemask().
> > > 
> > > Maybe the mempool tunable won't help much for your case if you need so
> > > many objects. It's still worth having a mempool for kmemleak but we
> > > could look into changing the refill logic while keeping the original
> > > size constant (say 1024 objects).
> > 
> > Actually, kmemleak.mempool=524288 works quite well on systems I have here.
> > This
> > is more of making the code robust by error-handling a large value without
> > the
> > NULL-ptr-deref below. Maybe simply just validate the value by adding upper
> > bound
> > to not trigger that warning with MAX_ORDER.
> 
> Would it work for you with a Kconfig option, similar to
> DEBUG_KMEMLEAK_EARLY_LOG_SIZE?

Yes, it should be fine.

> 
> > > > [   16.192449][    T1] BUG: Unable to handle kernel data access at
> > > > 0xffffffffffffb2aa
> > > 
> > > This doesn't seem kmemleak related from the trace.
> > 
> > This only happens when passing a large kmemleak.mempool, e.g., 64M
> > 
> > [   16.193126][    T1] NIP [c000000000b2a2fc] log_early+0x8/0x160
> > [   16.193153][    T1] LR [c0000000003e6e48] kmem_cache_free+0x428/0x740
> 
> Ah, I missed the log_early() call here. It's a kmemleak bug where it
> isn't disabled properly in case of an error and log_early() is still
> called after the .text.init section was freed. I'll send a patch.
>