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Date: Fri, 11 Sep 2020 09:09:39 +0200
From: peterz@infradead.org
Subject: Re: [RFC PATCH v2 1/3] mm/gup: fix gup_fast with dynamic page table
 folding
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To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, Dave Hansen <dave.hansen@linux.intel.com>, linux-mm <linux-mm@kvack.org>, Paul Mackerras <paulus@samba.org>, linux-sparc <sparclinux@vger.kernel.org>, Alexander Gordeev <agordeev@linux.ibm.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, Will Deacon <will@kernel.org>, linux-arch <linux-arch@vger.kernel.org>, linux-s390 <linux-s390@vger.kernel.org>, Vasily Gorbik <gor@linux.ibm.com>, Richard Weinberger <richard@nod.at>, linux-x86 <x86@kernel.org>, Russell King <linux@armlinux.org.uk>, Christian Borntraeger <borntraeger@de.ibm.com>, Ingo Molnar <mingo@redhat.com>, Catalin Marinas <catalin.marinas@arm.com>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Gerald Schaefer <gerald.schaefer@linux.ibm.com>, Heiko Carstens <hca@linux.ibm.com>, Arnd Bergmann <arnd@arndb.de>, John Hubbard <jhubbard@nvidia.com>, Jeff Dike <jdike@addtoit.com>, linux-um <linux-um@lists.infradead.org>, Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, linux-arm <linux-arm-kernel@lists.infradead.org>, Dave Hansen <dave.hansen@intel.com>, linux-power <linuxppc-dev@lists.ozlabs.org>, LKML <linux-kernel@vger.kernel.org>, Michael Ellerman <mpe@ellerman.id.au>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Mike Rapoport <rppt@kernel.org>

On Thu, Sep 10, 2020 at 06:59:21PM -0300, Jason Gunthorpe wrote:
> So, I suggest pXX_offset_unlocked()

Urgh, no. Elsewhere in gup _unlocked() means it will take the lock
itself (get_user_pages_unlocked()) -- although often it seems to mean
the lock is already held (git grep _unlocked and marvel).

What we want is _lockless().

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