K 10
svn:author
V 3
kib
K 8
svn:date
V 27
2019-09-09T11:22:38.499399Z
K 7
svn:log
V 730
Remove some unneeded vfs_busy() calls in SU code.

When softdep_fsync() is running, a caller must already started write
for the mount point.  Since unmount or remount to ro suspends mount
point, it cannot run in parallel with softdep_fsync(), which makes
vfs_busy() call there not needed.

Doing blocking vfs_busy() there effectively causes lock order reversal
between vn_start_write() and setting MNTK_UNMOUNT, because
vfs_busy(mp, 0) sleeps waiting for MNTK_UNMOUNT becoming clear, while
unmount sets the flag and starts the suspension.

Note that all other uses of vfs_busy() in SU code are non-blocking.

Reported by:	chs by mckusick
Reviewed by:	mckusick
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

END