RCUify freeing acls, let check_acl() go ahead in RCU mode if acl is cached
Al Viro [Wed, 3 Aug 2011 01:32:13 +0000 (21:32 -0400)]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c
include/linux/posix_acl.h

index 445fd5d..3d607bd 100644 (file)
@@ -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);
index a9c2fb2..b768110 100644 (file)
@@ -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);