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Date: Fri, 11 Mar 2016 00:54:50 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH] thp: fix deadlock in split_huge_pmd()
Message-ID: <20160310215450.GA129501@black.fi.intel.com>
References: <1457621646-119268-1-git-send-email-kirill.shutemov@linux.intel.com>
 <20160310115254.fe35ab2beca9690d4ee9989e@linux-foundation.org>
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To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org

On Thu, Mar 10, 2016 at 11:52:54AM -0800, Andrew Morton wrote:
> On Thu, 10 Mar 2016 17:54:06 +0300 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:
> 
> > split_huge_pmd() tries to munlock page with munlock_vma_page(). That
> > requires the page to locked.
> > 
> > If the is locked by caller, we would get a deadlock:
> > 
> > ...
> >
> > I don't think the deadlock is triggerable without split_huge_page()
> > simplifilcation patchset.
> > 
> > But munlock_vma_page() here is wrong: we want to munlock the page
> > unconditionally, no need in rmap lookup, that munlock_vma_page() does.
> > 
> > Let's use clear_page_mlock() instead. It can be called under ptl.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Fixes: ee0b79212791 ("thp: allow mlocked THP again")
> 
> This is the incorrect hash (or something weird happened at my end). 
> I'm seeing
> 
> commit e90309c9f7722db4ff5bce3b9e6e04d1460f2553
> Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Date:   Fri Jan 15 16:54:33 2016 -0800
> 
>     thp: allow mlocked THP again
> 
> That's the second time this has happened this week so please
> double-check whatever you're doing here?
> 
> 
> The patch itself doesn't apply to mainline, which is a bit strange
> given that it "Fixes" a bug in an already-mainlined patch.  The patch
> as-sent depends upon
> thp-rewrite-freeze_page-unfreeze_page-with-generic-rmap-walkers.patch,
> so I have queued it after that patch.

Here's a patch that can be applied mainline. Just in case.