[src/netbsd-6]: src/sys/ufs/ufs Pull up following revision(s) (requested by m...

[snj <snj%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ac2599f7d8f6
branches:  netbsd-6
changeset: 776802:ac2599f7d8f6
user:      snj <snj%NetBSD.org@localhost>
date:      Thu Dec 04 05:43:55 2014 +0000

description:
Pull up following revision(s) (requested by manu in ticket #1197):
        sys/ufs/ufs/ufs_extattr.c: revision 1.41, 1.45
Remove always-true condition and note that the current code is
suboptimal.
--
Fix UFS1 extended attribute backend autocreation deadlock
UFS1 extended attribute backend autocration goes through a vn_open()
to create the backend file, and this forces us to release the lock
on the target node, in case the target is within the parents of the
backend file. That created a window within which another thread could
acquire a lock on the target vnode and deadlock awaiting for the
mount extended attribute lock.
We fix the problem by also releasing the mount extended attribute lock
when calling vn_open(), but that lets another thread race us for backend
creation. We just detect this using O_EXCL for vn_open() and by checking
for EEXIST return code. If we are raced, we fail backend creation but
this is not a problem since another thread succeeded on it: we just have
to use the result.

diffstat:

 sys/ufs/ufs/ufs_extattr.c |  78 ++++++++++++++++++++++++++++++----------------
 1 files changed, 51 insertions(+), 27 deletions(-)

diffs (157 lines):

diff -r d0284dd3f67d -r ac2599f7d8f6 sys/ufs/ufs/ufs_extattr.c
--- a/sys/ufs/ufs/ufs_extattr.c Thu Dec 04 05:38:54 2014 +0000
+++ b/sys/ufs/ufs/ufs_extattr.c Thu Dec 04 05:43:55 2014 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: ufs_extattr.c,v 1.36.2.3 2014/12/04 05:38:54 snj Exp $ */
+/*     $NetBSD: ufs_extattr.c,v 1.36.2.4 2014/12/04 05:43:55 snj Exp $ */
 
 /*-
  * Copyright (c) 1999-2002 Robert N. M. Watson
@@ -48,7 +48,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: ufs_extattr.c,v 1.36.2.3 2014/12/04 05:38:54 snj Exp $");
+__KERNEL_RCSID(0, "$NetBSD: ufs_extattr.c,v 1.36.2.4 2014/12/04 05:43:55 snj Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ffs.h"
@@ -158,9 +158,9 @@
 /*
  * Autocreate an attribute storage
  */
-static struct ufs_extattr_list_entry *
+static int
 ufs_extattr_autocreate_attr(struct vnode *vp, int attrnamespace,
-    const char *attrname, struct lwp *l)
+    const char *attrname, struct lwp *l, struct ufs_extattr_list_entry **uelep)
 {
        struct mount *mp = vp->v_mount;
        struct ufsmount *ump = VFSTOUFS(mp);
@@ -194,38 +194,51 @@
                break;
        default:
                PNBUF_PUT(path);
-               return NULL;
+               *uelep = NULL;
+               return EINVAL;
                break;
        }
 
        /*
-        * When setting attribute on the root vnode, we get it 
-        * already locked, and vn_open/namei/VFS_ROOT will try to
-        * look it, causing a panic. Unlock it first.
+        * Release extended attribute mount lock, otherwise
+        * we can deadlock with another thread that would lock 
+        * vp after we unlock it below, and call 
+        * ufs_extattr_uepm_lock(ump), for instance
+        * in ufs_getextattr().
+        */
+       ufs_extattr_uepm_unlock(ump);
+
+       /*
+        * XXX unlock/lock should only be done when setting extattr
+        * on backing store or one of its parent directory 
+        * including root, but we always do it for now.
         */ 
-       if (vp->v_vflag && VV_ROOT) {
-               KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);
-               VOP_UNLOCK(vp);
-       }
-       KASSERT(VOP_ISLOCKED(vp) == 0);
+       KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);
+       VOP_UNLOCK(vp);
 
        pb = pathbuf_create(path);
        NDINIT(&nd, CREATE, LOCKPARENT, pb);
        
-       error = vn_open(&nd, O_CREAT|O_RDWR, 0600);
+       /*
+        * Since we do not hold ufs_extattr_uepm_lock anymore,
+        * another thread may race with us for backend creation,
+        * but only one can succeed here thanks to O_EXCL
+        */
+       error = vn_open(&nd, O_CREAT|O_EXCL|O_RDWR, 0600);
 
        /*
-        * Reacquire the lock on the vnode if it was root.
+        * Reacquire the lock on the vnode
         */
        KASSERT(VOP_ISLOCKED(vp) == 0);
-       if (vp->v_vflag && VV_ROOT)
-               vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
-       KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);
+       vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+
+       ufs_extattr_uepm_lock(ump);
 
        if (error != 0) {
                pathbuf_destroy(pb);
                PNBUF_PUT(path);
-               return NULL;
+               *uelep = NULL;
+               return error;
        }
 
        KASSERT(nd.ni_vp != NULL);
@@ -253,7 +266,8 @@
                printf("%s: write uef header failed for %s, error = %d\n", 
                       __func__, attrname, error);
                vn_close(backing_vp, FREAD|FWRITE, l->l_cred);
-               return NULL;
+               *uelep = NULL;
+               return error;
        }
 
        /*
@@ -266,7 +280,8 @@
                printf("%s: enable %s failed, error %d\n", 
                       __func__, attrname, error);
                vn_close(backing_vp, FREAD|FWRITE, l->l_cred);
-               return NULL;
+               *uelep = NULL;
+               return error;
        }
 
        uele = ufs_extattr_find_attr(ump, attrnamespace, attrname);
@@ -274,13 +289,15 @@
                printf("%s: atttribute %s created but not found!\n",
                       __func__, attrname);
                vn_close(backing_vp, FREAD|FWRITE, l->l_cred);
-               return NULL;
+               *uelep = NULL;
+               return ESRCH; /* really internal error */
        }
 
        printf("%s: EA backing store autocreated for %s\n",
               mp->mnt_stat.f_mntonname, attrname);
 
-       return uele;
+       *uelep = uele;
+       return 0;
 }
 
 /*
@@ -1343,10 +1360,17 @@
 
        attribute = ufs_extattr_find_attr(ump, attrnamespace, name);
        if (!attribute) {
-               attribute =  ufs_extattr_autocreate_attr(vp, attrnamespace, 
-                                                        name, l);
-               if  (!attribute)
-                       return (ENODATA);
+               error = ufs_extattr_autocreate_attr(vp, attrnamespace, 
+                                                   name, l, &attribute);
+               if (error == EEXIST) {
+                       /* Another thread raced us for backend creation */
+                       error = 0;
+                       attribute = 
+                           ufs_extattr_find_attr(ump, attrnamespace, name);
+               }
+
+               if (error || !attribute)
+                       return ENODATA;
        }
 
        /*