linux-kernel - Re: [PATCH] mm: mempool: Fix a possible sleep-in-atomic-context bug in mempool

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Date:   Thu, 21 Jun 2018 11:46:33 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     akpm@...ux-foundation.org, dvyukov@...gle.com,
        gregkh@...uxfoundation.org, jthumshirn@...e.de,
        pombredanne@...b.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: mempool: Fix a possible sleep-in-atomic-context bug
 in mempool_resize()



On 2018/6/21 11:38, Matthew Wilcox wrote:
> On Thu, Jun 21, 2018 at 11:07:14AM +0800, Jia-Ju Bai wrote:
>> The kernel may sleep with holding a spinlock.
>> The function call path (from bottom to top) in Linux-4.16.7 is:
>>
>> [FUNC] remove_element(GFP_KERNEL)
>> mm/mempool.c, 250: remove_element in mempool_resize
>> mm/mempool.c, 247: _raw_spin_lock_irqsave in mempool_resize
>>
>> To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.
>>
>> This bug is found by my static analysis tool (DSAC-2) and checked by
>> my code review.
> But ... we don't use the flags argument.
>
> static void *remove_element(mempool_t *pool, gfp_t flags)
> {
>          void *element = pool->elements[--pool->curr_nr];
>
>          BUG_ON(pool->curr_nr < 0);
>          kasan_unpoison_element(pool, element, flags);
>          check_element(pool, element);
>          return element;
> }
>
> ...
>
> static void kasan_unpoison_element(mempool_t *pool, void *element, gfp_t flags)
> {
>          if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc)
>                  kasan_unpoison_slab(element);
>          if (pool->alloc == mempool_alloc_pages)
>                  kasan_alloc_pages(element, (unsigned long)pool->pool_data);
> }
>
> So the correct patch would just remove this argument to remove_element() and
> kasan_unpoison_element()?

Yes, I also find this.
I can submit a patch that removes the flag in:
Definitions of kasan_unpoison_element() and remove_element()
Three calls to remove_element() and one call to kasan_unpoison_element() 
in mempool.c.

Do you think it is okay?


Best wishes,
Jia-Ju Bai