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Date: Tue, 5 Jan 2016 10:22:30 -0800
Message-ID: <CAPcyv4hYsnHoSFOgTFDtPaQkOq_N=evsKJsKsVe2_HbRfu5j9Q@mail.gmail.com>
Subject: Re: [PATCH v6 4/7] dax: add support for fsync/msync
From: Dan Williams <dan.j.williams@intel.com>
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To: Ross Zwisler <ross.zwisler@linux.intel.com>, Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "H. Peter Anvin" <hpa@zytor.com>, "J. Bruce Fields" <bfields@fieldses.org>, Theodore Ts'o <tytso@mit.edu>, Alexander Viro <viro@zeniv.linux.org.uk>, Andreas Dilger <adilger.kernel@dilger.ca>, Dave Chinner <david@fromorbit.com>, Ingo Molnar <mingo@redhat.com>, Jan Kara <jack@suse.com>, Jeff Layton <jlayton@poochiereds.net>, Matthew Wilcox <willy@linux.intel.com>, Thomas Gleixner <tglx@linutronix.de>, linux-ext4 <linux-ext4@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Linux MM <linux-mm@kvack.org>, "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>, X86 ML <x86@kernel.org>, XFS Developers <xfs@oss.sgi.com>, Andrew Morton <akpm@linux-foundation.org>, Matthew Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@linux.intel.com>

On Tue, Jan 5, 2016 at 10:14 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Tue, Jan 05, 2016 at 09:20:47AM -0800, Dan Williams wrote:
[..]
>> My concern is whether flushing potentially invalid virtual addresses
>> is problematic on some architectures.  Maybe it's just FUD, but it's
>> less work in my opinion to just revalidate the address versus auditing
>> each arch for this concern.
>
> I don't think that the addresses have the potential of being invalid from the
> driver's point of view - we are still holding a reference on the block queue
> via dax_map_atomic(), so we should be protected against races vs block device
> removal.  I think the only question is whether it is okay to flush an address
> that we know to be valid from the block device's point of view, but which the
> filesystem may have truncated from being allocated to our inode.
>
> Does that all make sense?

Yes, I was confusing which revalidation we were talking about.  As
long as the dax_map_atomic() is there I don't think we need any
further revalidation.

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