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Reply-To: "Hillf Danton" <hillf.zj@alibaba-inc.com>
From: "Hillf Danton" <hillf.zj@alibaba-inc.com>
References: <01fa01d1e94c$4be09210$e3a1b630$@alibaba-inc.com> <021901d1e96f$4b271830$e1754890$@alibaba-inc.com> <20160729081011.GA28534@black.fi.intel.com> <022c01d1e972$7ee5ada0$7cb108e0$@alibaba-inc.com> <20160729083115.GA24577@node.shutemov.name>
In-Reply-To: <20160729083115.GA24577@node.shutemov.name>
Subject: RE: [PATCH] mm: fail prefaulting if page table allocation fails
Date: Fri, 29 Jul 2016 16:40:56 +0800
Message-ID: <022d01d1e974$ece0ab00$c6a20100$@alibaba-inc.com>
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Sender: owner-linux-mm@kvack.org
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To: "'Kirill A. Shutemov'" <kirill@shutemov.name>
Cc: "'Kirill A. Shutemov'" <kirill.shutemov@linux.intel.com>, 'Vegard Nossum' <vegard.nossum@oracle.com>, 'Andrew Morton' <akpm@linux-foundation.org>, linux-mm@kvack.org

> > In filemap_map_pages()
> > 	CPU0					CPU1
> > 	trylock_page at offset_A		trylock_page at offset_A
> > 						goto offset_A+1
> > 	if (!fe->pte) {
> > 		alloc pte
> > 		map pte
> > 		lock pte
> > 	}
> > 	handle offset_A with ptl held		handle offset_A+1 without acquiring ptl
> 
> I still don't see where's the problem.
> 
> On the seond iteration (for offset_A+1), CPU1 would go into
> alloc_set_pte() and as its fe->pte is NULL pte_alloc_one_map() would map
> and lock the pte table allocated by CPU0.
> 
Ah, you are right. I missed the 2nd fe!

thanks
Hillf

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