Module Name: src
Committed By: manu
Date: Sat Nov 15 05:03:55 UTC 2014
Modified Files:
src/sys/ufs/ufs: ufs_extattr.c
Log Message:
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.
To generate a diff of this commit:
cvs rdiff -u -r1.44 -r1.45 src/sys/ufs/ufs/ufs_extattr.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/ufs/ufs/ufs_extattr.c
diff -u src/sys/ufs/ufs/ufs_extattr.c:1.44 src/sys/ufs/ufs/ufs_extattr.c:1.45
--- src/sys/ufs/ufs/ufs_extattr.c:1.44 Fri Nov 14 10:09:50 2014
+++ src/sys/ufs/ufs/ufs_extattr.c Sat Nov 15 05:03:55 2014
@@ -1,4 +1,4 @@
-/* $NetBSD: ufs_extattr.c,v 1.44 2014/11/14 10:09:50 manu Exp $ */
+/* $NetBSD: ufs_extattr.c,v 1.45 2014/11/15 05:03:55 manu 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 1.44 2014/11/14 10:09:50 manu Exp $");
+__KERNEL_RCSID(0, "$NetBSD: ufs_extattr.c,v 1.45 2014/11/15 05:03:55 manu Exp $");
#ifdef _KERNEL_OPT
#include "opt_ffs.h"
@@ -210,9 +210,9 @@ ufs_extattr_valid_attrname(int attrnames
/*
* 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);
@@ -246,11 +246,21 @@ ufs_extattr_autocreate_attr(struct vnode
break;
default:
PNBUF_PUT(path);
- return NULL;
+ *uelep = NULL;
+ return EINVAL;
break;
}
/*
+ * 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.
@@ -261,7 +271,12 @@ ufs_extattr_autocreate_attr(struct vnode
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
@@ -269,10 +284,13 @@ ufs_extattr_autocreate_attr(struct vnode
KASSERT(VOP_ISLOCKED(vp) == 0);
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);
@@ -300,7 +318,8 @@ ufs_extattr_autocreate_attr(struct vnode
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;
}
/*
@@ -313,7 +332,8 @@ ufs_extattr_autocreate_attr(struct vnode
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);
@@ -321,13 +341,15 @@ ufs_extattr_autocreate_attr(struct vnode
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;
}
/*
@@ -1405,10 +1427,17 @@ ufs_extattr_set(struct vnode *vp, int at
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;
}
/*
