linux-kernel - Re: [PATCH 1/2] zsmalloc: do not remap dst page while prepare next src page

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Date:	Wed, 25 Mar 2015 14:29:22 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Heesub Shin <heesub.shin@...sung.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Nitin Gupta <ngupta@...are.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	sunae.seo@...sung.com, cmlaika.kim@...sung.com
Subject: Re: [PATCH 1/2] zsmalloc: do not remap dst page while prepare next
 src page

On (03/25/15 14:05), Heesub Shin wrote:
> No, it's not unnecessary. We should do kunmap_atomic() in the reverse
> order of kmap_atomic(), so unfortunately it's inevitable to
> kunmap_atomic() both on d_addr and s_addr.
> 

Andrew, can you please drop this patch?


> > 
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> > ---
> >  mm/zsmalloc.c | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> > index d920e8b..7af4456 100644
> > --- a/mm/zsmalloc.c
> > +++ b/mm/zsmalloc.c
> > @@ -1536,12 +1536,10 @@ static void zs_object_copy(unsigned long src, unsigned long dst,
> >  			break;
> >  
> >  		if (s_off + size >= PAGE_SIZE) {
> > -			kunmap_atomic(d_addr);
> >  			kunmap_atomic(s_addr);
> 
> Removing kunmap_atomic(d_addr) here may cause BUG_ON() at __kunmap_atomic().
> 
> I tried yours to see it really happens:
> > kernel BUG at arch/arm/mm/highmem.c:113!

oh, arm. tested on x86_64 only. I see why it happens there. thanks for reporting.


sorry, should have checked.

> > Internal error: Oops - BUG: 0 [#1] SMP ARM
> > Modules linked in:
> > CPU: 2 PID: 1774 Comm: bash Not tainted 4.0.0-rc2-mm1+ #105
> > Hardware name: ARM-Versatile Express
> > task: ee971300 ti: e8a26000 task.ti: e8a26000
> > PC is at __kunmap_atomic+0x144/0x14c
> > LR is at zs_object_copy+0x19c/0x2dc

	-ss
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