static void nfs3_abort_get_acl(struct posix_acl **p)
{
struct posix_acl *sentinel = uncached_acl_sentinel(current);
/* Remove our sentinel upon failure. */
cmpxchg(p, sentinel, ACL_NOT_CACHED);
}
/*
* nfs3_prepare_get_acl, nfs3_complete_get_acl, nfs3_abort_get_acl: Helpers for
* caching get_acl results in a race-free way. See fs/posix_acl.c:get_acl()
* for explanations.
*/
static void nfs3_prepare_get_acl(struct posix_acl **p)
{
struct posix_acl *sentinel = uncached_acl_sentinel(current);
if (cmpxchg(p, ACL_NOT_CACHED, sentinel) != ACL_NOT_CACHED) {
/* Not the first reader or sentinel already in place. */
}
}
static void nfs3_complete_get_acl(struct posix_acl **p, struct posix_acl *acl)
{
struct posix_acl *sentinel = uncached_acl_sentinel(current);
/* Only cache the ACL if our sentinel is still in place. */
posix_acl_dup(acl);
if (cmpxchg(p, sentinel, acl) != sentinel)
posix_acl_release(acl);
}
struct posix_acl *get_acl(struct inode *inode, int type)
{
void *sentinel;
struct posix_acl **p;
struct posix_acl *acl;
/*
* The sentinel is used to detect when another operation like
* set_cached_acl() or forget_cached_acl() races with get_acl().
* It is guaranteed that is_uncached_acl(sentinel) is true.
*/
acl = get_cached_acl(inode, type);
if (!is_uncached_acl(acl))
return acl;
if (!IS_POSIXACL(inode))
return NULL;
sentinel = uncached_acl_sentinel(current);
p = acl_by_type(inode, type);
/*
* If the ACL isn't being read yet, set our sentinel. Otherwise, the
* current value of the ACL will not be ACL_NOT_CACHED and so our own
* sentinel will not be set; another task will update the cache. We
* could wait for that other task to complete its job, but it's easier
* to just call ->get_acl to fetch the ACL ourself. (This is going to
* be an unlikely race.)
*/
if (cmpxchg(p, ACL_NOT_CACHED, sentinel) != ACL_NOT_CACHED)
/* fall through */ ;
/*
* Normally, the ACL returned by ->get_acl will be cached.
* A filesystem can prevent that by calling
* forget_cached_acl(inode, type) in ->get_acl.
*
* If the filesystem doesn't have a get_acl() function at all, we'll
* just create the negative cache entry.
*/
if (!inode->i_op->get_acl) {
set_cached_acl(inode, type, NULL);
return NULL;
}
acl = inode->i_op->get_acl(inode, type);
if (IS_ERR(acl)) {
/*
* Remove our sentinel so that we don't block future attempts
* to cache the ACL.
*/
cmpxchg(p, sentinel, ACL_NOT_CACHED);
return acl;
}
/*
* Cache the result, but only if our sentinel is still in place.
*/
posix_acl_dup(acl);
if (unlikely(cmpxchg(p, sentinel, acl) != sentinel))
posix_acl_release(acl);
return acl;
}
