linux-kernel - Re: [RFC PATCH] mm: kasan: suppress soft lockup in slub when !CONFIG

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Date:   Thu, 7 Dec 2017 15:40:56 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Yang Shi <yang.s@...baba-inc.com>
Cc:     aryabinin@...tuozzo.com, glider@...gle.com, dvyukov@...gle.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: kasan: suppress soft lockup in slub when
 !CONFIG_PREEMPT

On Fri, Dec 08, 2017 at 07:30:07AM +0800, Yang Shi wrote:
> When running stress test with KASAN enabled, the below softlockup may
> happen occasionally:
> 
> NMI watchdog: BUG: soft lockup - CPU#7 stuck for 22s!
> hardirqs last  enabled at (0): [<          (null)>]      (null)
> hardirqs last disabled at (0): [] copy_process.part.30+0x5c6/0x1f50
> softirqs last  enabled at (0): [] copy_process.part.30+0x5c6/0x1f50
> softirqs last disabled at (0): [<          (null)>]      (null)

> Call Trace:
>  [] __slab_free+0x19c/0x270
>  [] ___cache_free+0xa6/0xb0
>  [] qlist_free_all+0x47/0x80
>  [] quarantine_reduce+0x159/0x190
>  [] kasan_kmalloc+0xaf/0xc0
>  [] kasan_slab_alloc+0x12/0x20
>  [] kmem_cache_alloc+0xfa/0x360
>  [] ? getname_flags+0x4f/0x1f0
>  [] getname_flags+0x4f/0x1f0
>  [] getname+0x12/0x20
>  [] do_sys_open+0xf9/0x210
>  [] SyS_open+0x1e/0x20
>  [] entry_SYSCALL_64_fastpath+0x1f/0xc2

This feels like papering over a problem.  KASAN only calls
quarantine_reduce() when it's allowed to block.  Presumably it has
millions of entries on the free list at this point.  I think the right
thing to do is for qlist_free_all() to call cond_resched() after freeing
every N items.

> The code is run in irq disabled or preempt disabled context, so
> cond_resched() can't be used in this case. Touch softlockup watchdog when
> KASAN is enabled to suppress the warning.
> 
> Signed-off-by: Yang Shi <yang.s@...baba-inc.com>
> ---
>  mm/slub.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index cfd56e5..4ae435e 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -35,6 +35,7 @@
>  #include <linux/prefetch.h>
>  #include <linux/memcontrol.h>
>  #include <linux/random.h>
> +#include <linux/nmi.h>
>  
>  #include <trace/events/kmem.h>
>  
> @@ -2266,6 +2267,10 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
>  		page->pobjects = pobjects;
>  		page->next = oldpage;
>  
> +#ifdef CONFIG_KASAN
> +		touch_softlockup_watchdog();
> +#endif
> +
>  	} while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page)
>  								!= oldpage);
>  	if (unlikely(!s->cpu_partial)) {
> -- 
> 1.8.3.1
> 
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