linux-ext4 - Re: [fstests PATCH] generic: add test for executables on read-only DAX mounts

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Message-ID: <20170831040255.GB17095@linux.intel.com>
Date:   Wed, 30 Aug 2017 22:02:55 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        fstests@...r.kernel.org, Eryu Guan <eguan@...hat.com>,
        linux-ext4@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, Randy Dodgen <rdodgen@...il.com>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [fstests PATCH] generic: add test for executables on read-only
 DAX mounts

On Wed, Aug 30, 2017 at 07:51:03AM -0700, Christoph Hellwig wrote:
> > The above patch fixes an issue with ext4 where executables cannot be run on
> > read-only filesystems mounted with the DAX option.
> > 
> > This issue does not appear to be present in ext2 or XFS, as they both pass
> > the test.  I've also confirmed outside of the test that they are both
> > indeed able to execute binaries on read-only DAX mounts.
> 
> It works for me on XFS.  But I don't really understand why, as the fault
> handler doesn't look very different.
> 
> Maybe the problem is that in ext4_journal_start_sb will fail on
> a read-only fs?
> 
> Even for xfs/ext2 it would seem odd that things like sb_start_pagefault
> just work. 
> 
> > +LS=$(which ls --skip-alias --skip-functions) 2>/dev/null
> > +if [ $? -ne 0 ]; then
> > +	status=$?
> > +	echo "Couldn't find 'ls'!?"
> > +	exit
> > +fi
> 
> These checks all fail for me..

Huh...really?  I'll send out v2 in a second, but if that fails for you as well
can you try and give me a hint as to what's going wrong with the test in your
setup?