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

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Date:   Wed, 31 Jul 2019 15:48:40 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Qian Cai <cai@....pw>
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, 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@....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?

> >> [   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.

-- 
Catalin