From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Junil Lee <junil0814.lee@lge.com>,
ngupta@vflare.org, akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, vbabka@suse.cz
Subject: Re: [PATCH v3] zsmalloc: fix migrate_zspage-zs_free race condition
Date: Mon, 18 Jan 2016 16:39:39 +0900 [thread overview]
Message-ID: <20160118073939.GA30668@swordfish> (raw)
In-Reply-To: <20160118071157.GD7453@bbox>
On (01/18/16 16:11), Minchan Kim wrote:
[..]
> > so, even if clear_bit_unlock/test_and_set_bit_lock do smp_mb or
> > barrier(), there is no corresponding barrier from record_obj()->WRITE_ONCE().
> > so I don't think WRITE_ONCE() will help the compiler, or am I missing
> > something?
>
> We need two things
thanks.
> 1. compiler barrier
um... probably gcc can reorder that sequence to something like this
*handle = obj_malloc() /* unpin the object */
zs_object_copy(*handle, used_obj, class) /* now use it*/
ok.
> 2. memory barrier.
>
> As compiler barrier, WRITE_ONCE works to prevent store tearing here
> by compiler.
> However, if we omit unpin_tag here, we lose memory barrier(e,g, smp_mb)
> so another CPU could see stale data caused CPU memory reordering.
oh... good find! lost release semantic of unpin_tag()...
-ss
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next prev parent reply other threads:[~2016-01-18 7:38 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-18 5:39 [PATCH v3] zsmalloc: fix migrate_zspage-zs_free race condition Junil Lee
2016-01-18 6:13 ` Sergey Senozhatsky
2016-01-18 6:36 ` Minchan Kim
2016-01-18 6:54 ` Sergey Senozhatsky
2016-01-18 7:11 ` Minchan Kim
2016-01-18 7:39 ` Sergey Senozhatsky [this message]
2016-01-18 7:54 ` Vlastimil Babka
2016-01-18 8:20 ` Minchan Kim
2016-01-18 11:08 ` Sergey Senozhatsky
2016-01-18 12:18 ` Vlastimil Babka
2016-01-18 14:09 ` Minchan Kim
2016-01-18 14:10 ` Vlastimil Babka
-- strict thread matches above, loose matches on Subject: below --
2016-01-18 1:15 Junil Lee
2016-01-18 4:14 ` Sergey Senozhatsky
2016-01-18 4:17 ` Sergey Senozhatsky
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