From: Vlastimil Babka <vbabka@suse.cz>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>,
Junil Lee <junil0814.lee@lge.com>,
ngupta@vflare.org, sergey.senozhatsky.work@gmail.com,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition
Date: Sat, 16 Jan 2016 09:16:41 +0100 [thread overview]
Message-ID: <5699FC69.4010000@suse.cz> (raw)
In-Reply-To: <20160116080650.GB566@swordfish>
On 16.1.2016 9:06, Sergey Senozhatsky wrote:
> On (01/16/16 08:44), Vlastimil Babka wrote:
>> On 16.1.2016 5:09, Sergey Senozhatsky wrote:
>>> On (01/15/16 16:49), Vlastimil Babka wrote:
>>
>> Hmm but that's an unpin, not a pin? A mistake or I'm missing something?
>
> I'm sure it's just a compose-in-mail-app typo.
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);
}
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?
> -ss
>
>> Anyway the compiler can do the same thing here without a WRITE_ONCE().
>
> --
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>
next prev parent reply other threads:[~2016-01-16 8:16 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-15 7:39 [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition Junil Lee
2016-01-15 14:34 ` Minchan Kim
2016-01-15 15:49 ` Vlastimil Babka
2016-01-16 4:09 ` Sergey Senozhatsky
2016-01-16 7:44 ` Vlastimil Babka
2016-01-16 8:06 ` Sergey Senozhatsky
2016-01-16 8:16 ` Vlastimil Babka [this message]
2016-01-16 10:05 ` Sergey Senozhatsky
2016-01-18 1:02 ` Junil Lee
2016-01-18 6:32 ` Minchan Kim
2016-01-18 7:04 ` Sergey Senozhatsky
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