Author: kib
Date: Mon Sep 9 11:22:38 2019
New Revision: 352058
URL: https://svnweb.freebsd.org/changeset/base/352058
Log:
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
Modified:
head/sys/ufs/ffs/ffs_softdep.c
Modified: head/sys/ufs/ffs/ffs_softdep.c
==============================================================================
--- head/sys/ufs/ffs/ffs_softdep.c Mon Sep 9 11:20:15 2019
(r352057)
+++ head/sys/ufs/ffs/ffs_softdep.c Mon Sep 9 11:22:38 2019
(r352058)
@@ -12507,24 +12507,13 @@ restart:
FREE_LOCK(ump);
if (ffs_vgetf(mp, parentino, LK_NOWAIT | LK_EXCLUSIVE, &pvp,
FFSV_FORCEINSMQ)) {
- error = vfs_busy(mp, MBF_NOWAIT);
- if (error != 0) {
- vfs_ref(mp);
- VOP_UNLOCK(vp, 0);
- error = vfs_busy(mp, 0);
- vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
- vfs_rel(mp);
- if (error != 0)
- return (ENOENT);
- if (vp->v_iflag & VI_DOOMED) {
- vfs_unbusy(mp);
- return (ENOENT);
- }
- }
+ /*
+ * Unmount cannot proceed after unlock because
+ * caller must have called vn_start_write().
+ */
VOP_UNLOCK(vp, 0);
error = ffs_vgetf(mp, parentino, LK_EXCLUSIVE,
&pvp, FFSV_FORCEINSMQ);
- vfs_unbusy(mp);
vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
if (vp->v_iflag & VI_DOOMED) {
if (error == 0)
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