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Groups > linux.kernel > #1310919
| From | Sergey Senozhatsky <sergey.senozhatsky@gmail.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition |
| Date | 2016-01-16 11:10 +0100 |
| Message-ID | <qRvXY-2Ws-13@gated-at.bofh.it> (permalink) |
| References | (2 earlier) <qReNs-89q-9@gated-at.bofh.it> <qRqvf-7Hg-3@gated-at.bofh.it> <qRtMu-1ox-1@gated-at.bofh.it> <qRu5Q-1Kr-9@gated-at.bofh.it> <qRufw-1NG-9@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On (01/16/16 09:16), Vlastimil Babka wrote:
[..]
> BTW, couldn't the correct fix also just look like this?
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 9f15bdd9163c..43f743175ede 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1635,8 +1635,8 @@ static int migrate_zspage(struct zs_pool *pool, struct
> size_class *class,
> free_obj = obj_malloc(d_page, class, handle);
> zs_object_copy(free_obj, used_obj, class);
> index++;
> + /* This also effectively unpins the handle */
> record_obj(handle, free_obj);
> - unpin_tag(handle);
> obj_free(pool, class, used_obj);
> }
I think this will work.
> But I'd still recommend WRITE_ONCE in record_obj(). And I'm not even sure it's
> safe on all architectures to do a simple overwrite of a word against somebody
> else trying to lock a bit there?
hm... for example, generic bitops from include/asm-generic/bitops/atomic.h
use _atomic_spin_lock_irqsave()
#define test_and_set_bit_lock(nr, addr) test_and_set_bit(nr, addr)
static inline int test_and_set_bit(int nr, volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
unsigned long old;
unsigned long flags;
_atomic_spin_lock_irqsave(p, flags);
old = *p;
*p = old | mask;
_atomic_spin_unlock_irqrestore(p, flags);
return (old & mask) != 0;
}
so overwriting it from the outside world (w/o taking _atomic_spin_lock_irqsave(p))
can theoretically be tricky in some cases.
-ss
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Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Minchan Kim <minchan@kernel.org> - 2016-01-15 15:40 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Vlastimil Babka <vbabka@suse.cz> - 2016-01-15 16:50 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-01-16 05:20 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Vlastimil Babka <vbabka@suse.cz> - 2016-01-16 08:50 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-01-16 09:10 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Vlastimil Babka <vbabka@suse.cz> - 2016-01-16 09:20 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-01-16 11:10 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Junil Lee <junil0814.lee@lge.com> - 2016-01-18 02:10 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Minchan Kim <minchan@kernel.org> - 2016-01-18 07:40 +0100
Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-18 08:10 +0100
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