From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f171.google.com (mail-io0-f171.google.com [209.85.223.171]) by kanga.kvack.org (Postfix) with ESMTP id 58E776B0005 for ; Sun, 17 Jan 2016 20:02:38 -0500 (EST) Received: by mail-io0-f171.google.com with SMTP id q21so535318926iod.0 for ; Sun, 17 Jan 2016 17:02:38 -0800 (PST) Received: from lgeamrelo11.lge.com (LGEAMRELO11.lge.com. [156.147.23.51]) by mx.google.com with ESMTPS id qb6si22614347igb.67.2016.01.17.17.02.36 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Sun, 17 Jan 2016 17:02:37 -0800 (PST) Subject: Re: [PATCH v2] zsmalloc: fix migrate_zspage-zs_free race condition References: <1452843551-4464-1-git-send-email-junil0814.lee@lge.com> <20160116100557.GC566@swordfish> From: Junil Lee Message-ID: <569C39A9.6050900@lge.com> Date: Mon, 18 Jan 2016 10:02:33 +0900 MIME-Version: 1.0 In-Reply-To: <20160116100557.GC566@swordfish> Content-Type: text/plain; charset=euc-kr Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Sergey Senozhatsky , Vlastimil Babka Cc: Minchan Kim , ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org 2016-01-16 ?AEA 7:05?! Sergey Senozhatsky AI(?!) 3/4 ' +-U: > 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. > I agree. And I tested previous patch as I sent, this problem has not been happened since 2 days ago. I will resend v3 as Babka. Thanks. > > > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org