linux-kernel - Re: [STABLE PATCH] slub: make ->cpu

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Message-ID: <20180930131026.GA25677@kroah.com>
Date:   Sun, 30 Sep 2018 06:10:26 -0700
From:   Greg KH <gregkh@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     zhong jiang <zhongjiang@...wei.com>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, mhocko@...nel.org, mgorman@...e.de,
        vbabka@...e.cz, andrea@...nel.org, kirill@...temov.name,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [STABLE PATCH] slub: make ->cpu_partial unsigned int

On Sun, Sep 30, 2018 at 05:50:38AM -0700, Matthew Wilcox wrote:
> On Sun, Sep 30, 2018 at 06:28:21PM +0800, zhong jiang wrote:
> > From: Alexey Dobriyan <adobriyan@...il.com>
> > 
> > [ Upstream commit e5d9998f3e09359b372a037a6ac55ba235d95d57 ]
> > 
> >         /*
> >          * cpu_partial determined the maximum number of objects
> >          * kept in the per cpu partial lists of a processor.
> >          */
> > 
> > Can't be negative.
> > 
> > I hit a real issue that it will result in a large number of memory leak.
> > Becuase Freeing slabs are in interrupt context. So it can trigger this issue.
> > put_cpu_partial can be interrupted more than once.
> > due to a union struct of lru and pobjects in struct page, when other core handles
> > page->lru list, for eaxmple, remove_partial in freeing slab code flow, It will
> > result in pobjects being a negative value(0xdead0000). Therefore, a large number
> > of slabs will be added to per_cpu partial list.
> > 
> > I had posted the issue to community before. The detailed issue description is as follows.
> > 
> > https://www.spinics.net/lists/kernel/msg2870979.html
> > 
> > After applying the patch, The issue is fixed. So the patch is a effective bugfix.
> > It should go into stable.
> > 
> > Link: http://lkml.kernel.org/r/20180305200730.15812-15-adobriyan@gmail.com
> > Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> > Acked-by: Christoph Lameter <cl@...ux.com>
> 
> Hang on.  Christoph acked the _original_ patch going into upstream.
> When he reviewed this patch for _stable_ last week, he asked for more
> investigation.  Including this patch in stable is misleading.

But the original patch has been in upstream for a long time now (it went
into 4.17-rc1).  If there was a real problem here, whouldn't it have
been resolved already?

And the patch in mainline has Christoph's ack...

thanks,

greg k-h