linux-ext4 - Re: dax pmd fault handler never returns to userspace

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Message-ID: <x49lh9vma41.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 18 Nov 2015 13:32:46 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Ross Zwisler <ross.zwisler@...el.com>
Subject: Re: dax pmd fault handler never returns to userspace

Ross Zwisler <ross.zwisler@...ux.intel.com> writes:

> Yea, my first round of testing was broken, sorry about that.
>
> It looks like this test causes the PMD fault handler to be called repeatedly
> over and over until you kill the userspace process.  This doesn't happen for
> XFS because when using XFS this test doesn't hit PMD faults, only PTE faults.

Hmm, I wonder why not?  Sounds like that will need investigating as
well, right?

-Jeff

> So, looks like a livelock as far as I can tell.
>
> Still debugging.

Thanks!
Jeff
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