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

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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2011-08-02 21:32:13 -04:00
parent 951c0d660a
commit 3567866bf2
2 changed files with 15 additions and 20 deletions
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17
fs/namei.c
View File

@ -179,19 +179,14 @@ static int check_acl(struct inode *inode, int mask)
#ifdef CONFIG_FS_POSIX_ACL #ifdef CONFIG_FS_POSIX_ACL
struct posix_acl *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 (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 -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); acl = get_cached_acl(inode, ACL_TYPE_ACCESS);

18
include/linux/posix_acl.h
View File

@ -9,6 +9,7 @@
#define __LINUX_POSIX_ACL_H #define __LINUX_POSIX_ACL_H
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/rcupdate.h>
#define ACL_UNDEFINED_ID (-1) #define ACL_UNDEFINED_ID (-1)
@ -38,7 +39,10 @@ struct posix_acl_entry {
}; };
struct posix_acl { struct posix_acl {
atomic_t a_refcount; union {
atomic_t a_refcount;
struct rcu_head a_rcu;
};
unsigned int a_count; unsigned int a_count;
struct posix_acl_entry a_entries[0]; struct posix_acl_entry a_entries[0];
}; };
@ -65,7 +69,7 @@ static inline void
posix_acl_release(struct posix_acl *acl) posix_acl_release(struct posix_acl *acl)
{ {
if (acl && atomic_dec_and_test(&acl->a_refcount)) 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; 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); return rcu_dereference(*acl_by_type(inode, type));
struct posix_acl *acl = ACCESS_ONCE(*p);
if (acl)
return 0;
return 1;
} }
static inline void set_cached_acl(struct inode *inode, 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; struct posix_acl *old;
spin_lock(&inode->i_lock); spin_lock(&inode->i_lock);
old = *p; old = *p;
*p = posix_dup_acl(acl); rcu_assign_pointer(*p, posix_acl_dup(acl));
spin_unlock(&inode->i_lock); spin_unlock(&inode->i_lock);
if (old != ACL_NOT_CACHED) if (old != ACL_NOT_CACHED)
posix_acl_release(old); posix_acl_release(old);