afs: Fix a Sparse warning in xdr_decode_AFSFetchStatus()

Sparse doesn't appear able to handle the conditionally-taken locks in
xdr_decode_AFSFetchStatus(), even though the lock and unlock are both
contingent on the same unvarying function argument.

Deal with this by interpolating a wrapper function that takes the lock if
needed and calls xdr_decode_AFSFetchStatus() on two separate branches, one
with the lock held and one without.

This allows Sparse to work out the locking.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 55 insertions, 42 deletions

diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index efacdb7c1dee..b695d9e16c65 100644
--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -137,10 +137,6 @@ static int xdr_decode_AFSFetchStatus(struct afs_call *call,
         u64 data_version, size;
         u32 type, abort_code;
         u8 flags = 0;
-        int ret;
-
-        if (vnode)
-                write_seqlock(&vnode->cb_lock);
 
         if (xdr->if_version != htonl(AFS_FSTATUS_VERSION)) {
                 pr_warn("Unknown AFSFetchStatus version %u\n", ntohl(xdr->if_version));
@@ -168,8 +164,7 @@ static int xdr_decode_AFSFetchStatus(struct afs_call *call,
         case AFS_FTYPE_INVALID:
                 if (abort_code != 0) {
                         status->abort_code = abort_code;
-                        ret = 0;
-                        goto out;
+                        return 0;
                 }
                 /* Fall through */
         default:
@@ -222,17 +217,35 @@ static int xdr_decode_AFSFetchStatus(struct afs_call *call,
                                              flags);
         }
 
-        ret = 0;
-
-out:
-        if (vnode)
-                write_sequnlock(&vnode->cb_lock);
-        return ret;
+        return 0;
 
 bad:
         xdr_dump_bad(*_bp);
-        ret = afs_protocol_error(call, -EBADMSG);
-        goto out;
+        return afs_protocol_error(call, -EBADMSG);
+}
+
+/*
+ * Decode the file status.  We need to lock the target vnode if we're going to
+ * update its status so that stat() sees the attributes update atomically.
+ */
+static int afs_decode_status(struct afs_call *call,
+                             const __be32 **_bp,
+                             struct afs_file_status *status,
+                             struct afs_vnode *vnode,
+                             const afs_dataversion_t *expected_version,
+                             struct afs_read *read_req)
+{
+        int ret;
+
+        if (!vnode)
+                return xdr_decode_AFSFetchStatus(call, _bp, status, vnode,
+                                                 expected_version, read_req);
+
+        write_seqlock(&vnode->cb_lock);
+        ret = xdr_decode_AFSFetchStatus(call, _bp, status, vnode,
+                                        expected_version, read_req);
+        write_sequnlock(&vnode->cb_lock);
+        return ret;
 }
 
 /*
@@ -374,8 +387,8 @@ static int afs_deliver_fs_fetch_status_vnode(struct afs_call *call)
 
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
-        if (xdr_decode_AFSFetchStatus(call, &bp, &vnode->status, vnode,
-                                      &call->expected_version, NULL) < 0)
+        if (afs_decode_status(call, &bp, &vnode->status, vnode,
+                              &call->expected_version, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         xdr_decode_AFSCallBack(call, vnode, &bp);
         if (call->reply[1])
@@ -555,8 +568,8 @@ static int afs_deliver_fs_fetch_data(struct afs_call *call)
                         return ret;
 
                 bp = call->buffer;
-                if (xdr_decode_AFSFetchStatus(call, &bp, &vnode->status, vnode,
-                                              &vnode->status.data_version, req) < 0)
+                if (afs_decode_status(call, &bp, &vnode->status, vnode,
+                                      &vnode->status.data_version, req) < 0)
                         return afs_protocol_error(call, -EBADMSG);
                 xdr_decode_AFSCallBack(call, vnode, &bp);
                 if (call->reply[1])
@@ -708,9 +721,9 @@ static int afs_deliver_fs_create_vnode(struct afs_call *call)
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
         xdr_decode_AFSFid(&bp, call->reply[1]);
-        if (xdr_decode_AFSFetchStatus(call, &bp, call->reply[2], NULL, NULL, NULL) < 0 ||
-            xdr_decode_AFSFetchStatus(call, &bp, &vnode->status, vnode,
-                                      &call->expected_version, NULL) < 0)
+        if (afs_decode_status(call, &bp, call->reply[2], NULL, NULL, NULL) < 0 ||
+            afs_decode_status(call, &bp, &vnode->status, vnode,
+                              &call->expected_version, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         xdr_decode_AFSCallBack_raw(&bp, call->reply[3]);
         /* xdr_decode_AFSVolSync(&bp, call->reply[X]); */
@@ -814,8 +827,8 @@ static int afs_deliver_fs_remove(struct afs_call *call)
 
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
-        if (xdr_decode_AFSFetchStatus(call, &bp, &vnode->status, vnode,
-                                      &call->expected_version, NULL) < 0)
+        if (afs_decode_status(call, &bp, &vnode->status, vnode,
+                              &call->expected_version, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         /* xdr_decode_AFSVolSync(&bp, call->reply[X]); */
 
@@ -904,9 +917,9 @@ static int afs_deliver_fs_link(struct afs_call *call)
 
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
-        if (xdr_decode_AFSFetchStatus(call, &bp, &vnode->status, vnode, NULL, NULL) < 0 ||
-            xdr_decode_AFSFetchStatus(call, &bp, &dvnode->status, dvnode,
-                                      &call->expected_version, NULL) < 0)
+        if (afs_decode_status(call, &bp, &vnode->status, vnode, NULL, NULL) < 0 ||
+            afs_decode_status(call, &bp, &dvnode->status, dvnode,
+                              &call->expected_version, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         /* xdr_decode_AFSVolSync(&bp, call->reply[X]); */
 
@@ -991,9 +1004,9 @@ static int afs_deliver_fs_symlink(struct afs_call *call)
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
         xdr_decode_AFSFid(&bp, call->reply[1]);
-        if (xdr_decode_AFSFetchStatus(call, &bp, call->reply[2], NULL, NULL, NULL) ||
-            xdr_decode_AFSFetchStatus(call, &bp, &vnode->status, vnode,
-                                      &call->expected_version, NULL) < 0)
+        if (afs_decode_status(call, &bp, call->reply[2], NULL, NULL, NULL) ||
+            afs_decode_status(call, &bp, &vnode->status, vnode,
+                              &call->expected_version, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         /* xdr_decode_AFSVolSync(&bp, call->reply[X]); */
 
@@ -1097,12 +1110,12 @@ static int afs_deliver_fs_rename(struct afs_call *call)
 
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
-        if (xdr_decode_AFSFetchStatus(call, &bp, &orig_dvnode->status, orig_dvnode,
-                                      &call->expected_version, NULL) < 0)
+        if (afs_decode_status(call, &bp, &orig_dvnode->status, orig_dvnode,
+                              &call->expected_version, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         if (new_dvnode != orig_dvnode &&
-            xdr_decode_AFSFetchStatus(call, &bp, &new_dvnode->status, new_dvnode,
-                                      &call->expected_version_2, NULL) < 0)
+            afs_decode_status(call, &bp, &new_dvnode->status, new_dvnode,
+                              &call->expected_version_2, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         /* xdr_decode_AFSVolSync(&bp, call->reply[X]); */
 
@@ -1206,8 +1219,8 @@ static int afs_deliver_fs_store_data(struct afs_call *call)
 
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
-        if (xdr_decode_AFSFetchStatus(call, &bp, &vnode->status, vnode,
-                                      &call->expected_version, NULL) < 0)
+        if (afs_decode_status(call, &bp, &vnode->status, vnode,
+                              &call->expected_version, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         /* xdr_decode_AFSVolSync(&bp, call->reply[X]); */
 
@@ -1382,8 +1395,8 @@ static int afs_deliver_fs_store_status(struct afs_call *call)
 
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
-        if (xdr_decode_AFSFetchStatus(call, &bp, &vnode->status, vnode,
-                                      &call->expected_version, NULL) < 0)
+        if (afs_decode_status(call, &bp, &vnode->status, vnode,
+                              &call->expected_version, NULL) < 0)
                 return afs_protocol_error(call, -EBADMSG);
         /* xdr_decode_AFSVolSync(&bp, call->reply[X]); */
 
@@ -2084,8 +2097,8 @@ static int afs_deliver_fs_fetch_status(struct afs_call *call)
 
         /* unmarshall the reply once we've received all of it */
         bp = call->buffer;
-        xdr_decode_AFSFetchStatus(call, &bp, status, vnode,
-                                  &call->expected_version, NULL);
+        afs_decode_status(call, &bp, status, vnode,
+                          &call->expected_version, NULL);
         callback[call->count].version   = ntohl(bp[0]);
         callback[call->count].expiry    = ntohl(bp[1]);
         callback[call->count].type      = ntohl(bp[2]);
@@ -2196,9 +2209,9 @@ static int afs_deliver_fs_inline_bulk_status(struct afs_call *call)
 
                 bp = call->buffer;
                 statuses = call->reply[1];
-                if (xdr_decode_AFSFetchStatus(call, &bp, &statuses[call->count],
-                                              call->count == 0 ? vnode : NULL,
-                                              NULL, NULL) < 0)
+                if (afs_decode_status(call, &bp, &statuses[call->count],
+                                      call->count == 0 ? vnode : NULL,
+                                      NULL, NULL) < 0)
                         return afs_protocol_error(call, -EBADMSG);
 
                 call->count++;