binary execution from DAX mount hang since next-20160407

[Xiong Zhou]

Hi, all

Since tag next-20160407 in linux-next repo, executing binary
from/in DAX mount hangs.

It does not hang if mount without dax option.
It hangs with both xfs and ext4.
It does not hang if execute from a -t tmpfs mount.
It does not hang on next-20160406 and still hangs on 0414 tree.

# ps -axjf
...
S+       0   0:00  |       \_ sh -x thl.sh
R+       0  42:33  |           \_ [hl]
..
# cat thl.sh
mkfs.ext4 /dev/pmem0
mount -o dax /dev/pmem0 /daxmnt
cp hl /daxmnt
/daxmnt/hl
# cat hl.c
void main()
{
        printf("ok\n");
}
# cc hl.c -o hl

Bisecting commits between 0406 and 0407 tag, points to this:

d7c7d56ca61aec18e5e0cb3a64e50073c42195f7 is the first bad commit
commit d7c7d56ca61aec18e5e0cb3a64e50073c42195f7
Author: Hugh Dickins <hughd@xxxxxxxxxx>
Date:   Thu Apr 7 14:00:12 2016 +1000

    huge tmpfs: avoid premature exposure of new pagetable

Bisect log and config are attatched.

Thanks,
Xiong

Attachment: config
Description: Binary data

Attachment: bisectlog
Description: Binary data