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>
diff --git a/fs/namei.c b/fs/namei.c
index 445fd5d..3d607bd 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -179,19 +179,14 @@
#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 a9c2fb2..b768110 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 {
- 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 @@
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 @@
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 @@
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);