CVS commit: src/sys/kern

["Emmanuel Dreyfus" <manu%netbsd.org@localhost>]

Module Name:    src
Committed By:   manu
Date:           Sun Aug  2 03:29:22 UTC 2015

Modified Files:
        src/sys/kern: vfs_mount.c

Log Message:
Do not VFS_SYNC before VFS_UNMOUNT on force unmount

VFS_SYNC does not consider whether we are performing a force unmount or not,
and therefore it can wait for a while if the filesytstem is misbehaving.
Removing VFS_SYNC before VFS_UNMOUNT on forced unmount fixes the problem.

This should not cause harm as the VFS_SYNC seems just useless.
As noted by Chuck Silvers in
http://mail-index.netbsd.org/tech-kern/2015/07/13/msg019156.html
- Nothing seems to prevent vnodes from getting dirty again after VFS_SYNC call.
- Filesystems do flush data through vflush() in VFS_UNMOUNT anyway.

As a consequence, the VFS_SYNC call in do_unmount() could probably be
completely removed. But since such a change is quite dangerous, we just
remove it in the case of forced unmounts, which are situations where
the risk of data loss is known to the operator.


To generate a diff of this commit:
cvs rdiff -u -r1.35 -r1.36 src/sys/kern/vfs_mount.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.