The branch main has been updated by mjg:
URL:
https://cgit.FreeBSD.org/src/commit/?id=dbc689cdef0cc8ff11171642cdcf107dfbc3fb41
commit dbc689cdef0cc8ff11171642cdcf107dfbc3fb41
Author: Mateusz Guzik <m...@freebsd.org>
AuthorDate: 2021-08-18 21:14:16 +0000
Commit: Mateusz Guzik <m...@freebsd.org>
CommitDate: 2021-08-20 17:52:24 +0000
vfs: use vn_lock_pair to avoid establishing an ordering on mount
This fixes some of the LORs seen on mount/unmount.
Complete fix will require taking care of unmount as well.
Reviewed by: kib
Tested by: pho (previous version)
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D31611
---
sys/kern/vfs_mount.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index 3c546392b213..92e70e45d46e 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -1191,19 +1191,28 @@ vfs_domount_first(
mp->mnt_kern_flag &= ~MNTK_ASYNC;
MNT_IUNLOCK(mp);
- vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
- cache_purge(vp);
VI_LOCK(vp);
- vp->v_iflag &= ~VI_MOUNT;
+ cache_purge(vp);
vn_irflag_set_locked(vp, VIRF_MOUNTPOINT);
vp->v_mountedhere = mp;
VI_UNLOCK(vp);
+
+ /*
+ * We need to lock both vnodes.
+ *
+ * Use vn_lock_pair to avoid establishing an ordering between vnodes
+ * from different filesystems.
+ */
+ vn_lock_pair(vp, false, newdp, false);
+
+ VI_LOCK(vp);
+ vp->v_iflag &= ~VI_MOUNT;
+ VI_UNLOCK(vp);
/* Place the new filesystem at the end of the mount list. */
mtx_lock(&mountlist_mtx);
TAILQ_INSERT_TAIL(&mountlist, mp, mnt_list);
mtx_unlock(&mountlist_mtx);
vfs_event_signal(NULL, VQ_MOUNT, 0);
- vn_lock(newdp, LK_EXCLUSIVE | LK_RETRY);
VOP_UNLOCK(vp);
EVENTHANDLER_DIRECT_INVOKE(vfs_mounted, mp, newdp, td);
VOP_UNLOCK(newdp);
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