umount mfs crash - Fatal trap 12
Using fresh master (January 17th 2012),
umount of mfs mount crashes system.
This happens every time; core dump avail on request.
Fatal trap 12: page fault while in kernel mode
#1 Updated by ftigeot almost 5 years ago
On Tue, Jan 17, 2012 at 10:30:04AM -0800, Thomas Nikolajsen via Redmine wrote:
> Issue #2276 has been reported by Thomas Nikolajsen.
> Bug #2276: umount mfs crash - Fatal trap 12
> Using fresh master (January 17th 2012),
> umount of mfs mount crashes system.
> This happens every time; core dump avail on request.
I cannot reproduce this. Can you please make the core available and write
the exact sequence of commands you use to make your system crash ?
#2 Updated by thomas.nikolajsen almost 5 years ago
Core dump uploaded to leaf: ~thomas/crash/38
How to reproduce (results in immediate crash here every time):
on i386 (didn't try x86_64 yet)
# mount mfs file system, and umount i again
mount -t mfs -o -s=655360 swap /boot/tmp2
#4 Updated by me1 almost 5 years ago
Here's the problem:
MFS's mfs_start() routine is not like other filesystems; the userland mount_mfs enters the mfs_start routine and processes copyin/copyout requests to transfer data into its userland mmap-ed region. When it returns after either being signalled or the filesystem being unmounted, the mount structure is not valid.
Unfortunately, sys_unmount() already kfree-d the mount structure; both the accounting init and MPUNLOCK(mp) in vfs_vfsops.c:vfs_start() are not safe; they are accessing the mountpoint after it is freed.