DragonFly bugs List (threaded) for 2012-02
[DragonFlyBSD - Bug #2276] umount mfs crash - Fatal trap 12
Issue #2276 has been updated by Venkatesh Srinivas.
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.
Bug #2276: umount mfs crash - Fatal trap 12
Author: Thomas Nikolajsen
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
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