Resolve the devfs deadlock caused by LOR between devfs_mount->dm_lock and

vnode lock in devfs_allocv. Do this by temporary dropping dm_lock around
vnode locking.

For safe operation, add hold counters for both devfs_mount and devfs_dirent,
and DE_DOOMED flag for devfs_dirent. The facilities allow to continue after
dropping of the dm_lock, by making sure that referenced memory does not
disappear.

Reviewed by:	tegge
Tested by:	kris
Approved by:	kan (mentor)
PR:		kern/102335

1 files changed, 12 insertions, 1 deletions

diff --git a/sys/fs/devfs/devfs_devs.c b/sys/fs/devfs/devfs_devs.c
index d933f9f..c8408ce 100644
--- a/sys/fs/devfs/devfs_devs.c
+++ b/sys/fs/devfs/devfs_devs.c
@@ -179,6 +179,7 @@ devfs_newdirent(char *name, int namelen)
 	vfs_timestamp(&de->de_ctime);
 	de->de_mtime = de->de_atime = de->de_ctime;
 	de->de_links = 1;
+	de->de_holdcnt = 1;
 #ifdef MAC
 	mac_init_devfsdirent(de);
 #endif
@@ -230,9 +231,18 @@ devfs_vmkdir(struct devfs_mount *dmp, char *name, int namelen, struct devfs_dire
 }
 
 void
+devfs_dirent_free(struct devfs_dirent *de)
+{
+	free(de, M_DEVFS3);
+}
+
+void
 devfs_delete(struct devfs_mount *dm, struct devfs_dirent *de)
 {
 
+	KASSERT((de->de_flags & DE_DOOMED) == 0,
+		("devfs_delete doomed dirent"));
+	de->de_flags |= DE_DOOMED;
 	if (de->de_symlink) {
 		free(de->de_symlink, M_DEVFS);
 		de->de_symlink = NULL;
@@ -251,7 +261,8 @@ devfs_delete(struct devfs_mount *dm, struct devfs_dirent *de)
 		free_unr(devfs_inos, de->de_inode);
 		de->de_inode = 0;
 	}
-	free(de, M_DEVFS3);
+	if (DEVFS_DE_DROP(de))
+		devfs_dirent_free(de);
 }
 
 /*