linux-kernel - Re: [PATCH] mm/huge_memory: fix the memory leak due to the race

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Message-ID: <20160621152920.GA7760@node.shutemov.name>
Date:	Tue, 21 Jun 2016 18:29:20 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	zhong jiang <zhongjiang@...wei.com>
Cc:	mhocko@...nel.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/huge_memory: fix the memory leak due to the race

On Tue, Jun 21, 2016 at 11:19:07PM +0800, zhong jiang wrote:
> On 2016/6/21 22:37, Kirill A. Shutemov wrote:
> > On Tue, Jun 21, 2016 at 10:05:56PM +0800, zhongjiang wrote:
> >> From: zhong jiang <zhongjiang@...wei.com>
> >>
> >> with great pressure, I run some test cases. As a result, I found
> >> that the THP is not freed, it is detected by check_mm().
> >>
> >> BUG: Bad rss-counter state mm:ffff8827edb70000 idx:1 val:512
> >>
> >> Consider the following race :
> >>
> >> 	CPU0                               CPU1
> >>   __handle_mm_fault()
> >>         wp_huge_pmd()
> >>    	    do_huge_pmd_wp_page()
> >> 		pmdp_huge_clear_flush_notify()
> >>                 (pmd_none = true)
> >> 					exit_mmap()
> >> 					   unmap_vmas()
> >> 					     zap_pmd_range()
> >> 						pmd_none_or_trans_huge_or_clear_bad()
> >> 						   (result in memory leak)
> >>                 set_pmd_at()
> >>
> >> because of CPU0 have allocated huge page before pmdp_huge_clear_notify,
> >> and it make the pmd entry to be null. Therefore, The memory leak can occur.
> >>
> >> The patch fix the scenario that the pmd entry can lead to be null.
> > I don't think the scenario is possible.
> >
> > exit_mmap() called when all mm users have gone, so no parallel threads
> > exist.
> >
>  Forget  this patch.  It 's my fault , it indeed don not exist.
>  But I  hit the following problem.  we can see the memory leak when the process exit.
>  
>  
>  Any suggestion will be apprecaited.

Could you try this:

http://lkml.kernel.org/r/20160621150433.GA7536@node.shutemov.name

-- 
 Kirill A. Shutemov