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

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Message-ID: <20170830145103.GA10163@infradead.org>
Date:   Wed, 30 Aug 2017 07:51:03 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     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>,
        Christoph Hellwig <hch@...radead.org>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [fstests PATCH] generic: add test for executables on read-only
 DAX mounts

> 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..