From: Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v6 4/7] dax: add support for fsync/msync
Date: Tue, 5 Jan 2016 10:22:30 -0800
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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.