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DragonFly bugs List (threaded) for 2012-02
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[DragonFlyBSD - Bug #2276] umount mfs crash - Fatal trap 12

From: Venkatesh Srinivas via Redmine <bugtracker-admin@xxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 16 Feb 2012 05:54:56 -0800

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
Status: New
Priority: Normal
Target version: 

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
> trace

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