Move the prepare_get_acl, complete_get_acl, and abort_get_acl helpers
from fs/nfs/nfs3acl.c to fs/posix_acl.c: using the same helpers in
get_acl and in nfs3_get_acl makes the code easier to read.
In get_acl, move the check for NULL get_acl inode operations above
__prepare_get_acl.
Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
---
fs/nfs/nfs3acl.c | 44 +++---------------
fs/posix_acl.c | 116 ++++++++++++++++++++++++++++++++--------------
include/linux/posix_acl.h | 4 ++
3 files changed, 90 insertions(+), 74 deletions(-)
diff --git a/fs/nfs/nfs3acl.c b/fs/nfs/nfs3acl.c
index 720d92f5..b623801 100644
--- a/fs/nfs/nfs3acl.c
+++ b/fs/nfs/nfs3acl.c
@@ -11,38 +11,6 @@
#define NFSDBG_FACILITY NFSDBG_PROC
-/*
- * 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);
-}
-
-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);
-}
-
struct posix_acl *nfs3_get_acl(struct inode *inode, int type)
{
struct nfs_server *server = NFS_SERVER(inode);
@@ -88,9 +56,9 @@ struct posix_acl *nfs3_get_acl(struct inode *inode, int type)
return ERR_PTR(-ENOMEM);
if (args.mask & NFS_ACL)
- nfs3_prepare_get_acl(&inode->i_acl);
+ prepare_get_acl(inode, ACL_TYPE_ACCESS);
if (args.mask & NFS_DFACL)
- nfs3_prepare_get_acl(&inode->i_default_acl);
+ prepare_get_acl(inode, ACL_TYPE_DEFAULT);
status = rpc_call_sync(server->client_acl, &msg, 0);
dprintk("NFS reply getacl: %d\n", status);
@@ -126,12 +94,12 @@ struct posix_acl *nfs3_get_acl(struct inode *inode, int type)
}
if (res.mask & NFS_ACL)
- nfs3_complete_get_acl(&inode->i_acl, res.acl_access);
+ complete_get_acl(inode, ACL_TYPE_ACCESS, res.acl_access);
else
forget_cached_acl(inode, ACL_TYPE_ACCESS);
if (res.mask & NFS_DFACL)
- nfs3_complete_get_acl(&inode->i_default_acl, res.acl_default);
+ complete_get_acl(inode, ACL_TYPE_DEFAULT, res.acl_default);
else
forget_cached_acl(inode, ACL_TYPE_DEFAULT);
@@ -145,8 +113,8 @@ struct posix_acl *nfs3_get_acl(struct inode *inode, int type)
}
getout:
- nfs3_abort_get_acl(&inode->i_acl);
- nfs3_abort_get_acl(&inode->i_default_acl);
+ abort_get_acl(inode, ACL_TYPE_ACCESS);
+ abort_get_acl(inode, ACL_TYPE_DEFAULT);
posix_acl_release(res.acl_access);
posix_acl_release(res.acl_default);
nfs_free_fattr(res.fattr);
diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 59d47ab0..0be840e 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -91,18 +91,80 @@ void forget_all_cached_acls(struct inode *inode)
}
EXPORT_SYMBOL(forget_all_cached_acls);
+static bool __prepare_get_acl(struct posix_acl **p)
+{
+ struct posix_acl *sentinel = uncached_acl_sentinel(current);
+
+ return cmpxchg(p, ACL_NOT_CACHED, sentinel) == ACL_NOT_CACHED;
+}
+
+bool prepare_get_acl(struct inode *inode, int type)
+{
+ return __prepare_get_acl(acl_by_type(inode, type));
+}
+EXPORT_SYMBOL(prepare_get_acl);
+
+/* Only cache the ACL if our sentinel is still in place. */
+static void __complete_get_acl(struct posix_acl **p, struct posix_acl *acl)
+{
+ struct posix_acl *sentinel = uncached_acl_sentinel(current);
+
+ posix_acl_dup(acl);
+ if (cmpxchg(p, sentinel, acl) != sentinel)
+ posix_acl_release(acl);
+}
+
+void complete_get_acl(struct inode *inode, int type, struct posix_acl *acl)
+{
+ return __complete_get_acl(acl_by_type(inode, type), acl);
+}
+EXPORT_SYMBOL(complete_get_acl);
+
+/* Remove our sentinel upon failure. */
+/*
+ * Remove our sentinel so that we don't block future attempts
+ * to cache the ACL.
+ */
+static void __abort_get_acl(struct posix_acl **p)
+{
+ struct posix_acl *sentinel = uncached_acl_sentinel(current);
+
+ cmpxchg(p, sentinel, ACL_NOT_CACHED);
+}
+
+void abort_get_acl(struct inode *inode, int type)
+{
+ __abort_get_acl(acl_by_type(inode, type));
+}
+EXPORT_SYMBOL(abort_get_acl);
+
+
+/**
+ * get_acl - Get the ACL of an inode
+ *
+ * This function is called without holding the inode mutex, so when fetching an
+ * uncached ACL from the filesystem, we can race with other get_acl or set_acl
+ * requests. We must make sure not to override ACLs set with set_acl in the
+ * meantime.
+ *
+ * To do that, we change ->i_acl (or ->i_default_acl) from ACL_NOT_CACHED to a
+ * sentinel value that indicates that get_acl is in progress (prepare_get_acl).
+ * For these sentinel values, is_uncached_acl(sentinel) is always true.
+ *
+ * When we get back an ACL from the filesystem, we update the cached ACL only
+ * if our sentinel value is still in place ( complete_get_acl).
+ *
+ * A competing set_acl will replace our sentinel with the new ACL, and
+ * complete_get_acl will leave that new ACL untouched.
+ *
+ * When get_acl fails, we remove our sentinel so that future attempts to cache
+ * the ACL can succeed (abort_get_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;
@@ -110,25 +172,7 @@ struct posix_acl *get_acl(struct inode *inode, int type)
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.
*/
@@ -136,23 +180,23 @@ struct posix_acl *get_acl(struct inode *inode, int type)
set_cached_acl(inode, type, NULL);
return NULL;
}
+
+ p = acl_by_type(inode, type);
+ __prepare_get_acl(p);
+
+ /*
+ * 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.
+ */
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);
+ __abort_get_acl(p);
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);
+ __complete_get_acl(p, acl);
return acl;
}
EXPORT_SYMBOL(get_acl);
diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h
index d5d3d74..b150e76 100644
--- a/include/linux/posix_acl.h
+++ b/include/linux/posix_acl.h
@@ -136,6 +136,10 @@ static inline void forget_all_cached_acls(struct inode *inode)
}
#endif /* CONFIG_FS_POSIX_ACL */
+bool prepare_get_acl(struct inode *, int);
+void complete_get_acl(struct inode *, int, struct posix_acl *);
+void abort_get_acl(struct inode *, int);
+
struct posix_acl *get_acl(struct inode *inode, int type);
#endif /* __LINUX_POSIX_ACL_H */
--
2.7.4
--
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