RCUify freeing acls, let check_acl() go ahead in RCU mode if acl is cached

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 15 insertions, 20 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 445fd5da11fa..3d607bd80e09 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -179,19 +179,14 @@ static int check_acl(struct inode *inode, int mask)
 #ifdef CONFIG_FS_POSIX_ACL
         struct posix_acl *acl;
 
-        /*
-         * Under RCU walk, we cannot even do a "get_cached_acl()",
-         * because that involves locking and getting a refcount on
-         * a cached ACL.
-         *
-         * So the only case we handle during RCU walking is the
-         * case of a cached "no ACL at all", which needs no locks
-         * or refcounts.
-         */
         if (mask & MAY_NOT_BLOCK) {
-                if (negative_cached_acl(inode, ACL_TYPE_ACCESS))
+                acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS);
+                if (!acl)
                         return -EAGAIN;
-                return -ECHILD;
+                /* no ->get_acl() calls in RCU mode... */
+                if (acl == ACL_NOT_CACHED)
+                        return -ECHILD;
+                return posix_acl_permission(inode, acl, mask);
         }
 
         acl = get_cached_acl(inode, ACL_TYPE_ACCESS);
diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h
index a9c2fb29be96..b7681102a4b9 100644
--- a/include/linux/posix_acl.h
+++ b/include/linux/posix_acl.h
@@ -9,6 +9,7 @@
 #define __LINUX_POSIX_ACL_H
 
 #include <linux/slab.h>
+#include <linux/rcupdate.h>
 
 #define ACL_UNDEFINED_ID        (-1)
 
@@ -38,7 +39,10 @@ struct posix_acl_entry {
 };
 
 struct posix_acl {
-        atomic_t                a_refcount;
+        union {
+                atomic_t                a_refcount;
+                struct rcu_head         a_rcu;
+        };
         unsigned int            a_count;
         struct posix_acl_entry  a_entries[0];
 };
@@ -65,7 +69,7 @@ static inline void
 posix_acl_release(struct posix_acl *acl)
 {
         if (acl && atomic_dec_and_test(&acl->a_refcount))
-                kfree(acl);
+                kfree_rcu(acl, a_rcu);
 }
 
 
@@ -110,13 +114,9 @@ static inline struct posix_acl *get_cached_acl(struct inode *inode, int type)
         return acl;
 }
 
-static inline int negative_cached_acl(struct inode *inode, int type)
+static inline struct posix_acl *get_cached_acl_rcu(struct inode *inode, int type)
 {
-        struct posix_acl **p = acl_by_type(inode, type);
-        struct posix_acl *acl = ACCESS_ONCE(*p);
-        if (acl)
-                return 0;
-        return 1;
+        return rcu_dereference(*acl_by_type(inode, type));
 }
 
 static inline void set_cached_acl(struct inode *inode,
@@ -127,7 +127,7 @@ static inline void set_cached_acl(struct inode *inode,
         struct posix_acl *old;
         spin_lock(&inode->i_lock);
         old = *p;
-        *p = posix_dup_acl(acl);
+        rcu_assign_pointer(*p, posix_acl_dup(acl));
         spin_unlock(&inode->i_lock);
         if (old != ACL_NOT_CACHED)
                 posix_acl_release(old);