On Wed, Aug 30, 2017 at 07:51:03AM -0700, Christoph Hellwig wrote:

quoted

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. 

quoted

+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?