afs: Make vnode->cb_interest RCU safe

Use RCU-based freeing for afs_cb_interest struct objects and use RCU on
vnode->cb_interest.  Use that change to allow afs_check_validity() to use
read_seqbegin_or_lock() instead of read_seqlock_excl().

This also requires the caller of afs_check_validity() to hold the RCU read
lock across the call.

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

1 files changed, 12 insertions, 6 deletions

diff --git a/fs/afs/rotate.c b/fs/afs/rotate.c
index 52f3a9910f0d..b00c739e0e63 100644
--- a/fs/afs/rotate.c
+++ b/fs/afs/rotate.c
@@ -66,7 +66,8 @@ static bool afs_start_fs_iteration(struct afs_fs_cursor *fc,
         fc->untried = (1UL << fc->server_list->nr_servers) - 1;
         fc->index = READ_ONCE(fc->server_list->preferred);
 
-        cbi = vnode->cb_interest;
+        cbi = rcu_dereference_protected(vnode->cb_interest,
+                                        lockdep_is_held(&vnode->io_lock));
         if (cbi) {
                 /* See if the vnode's preferred record is still available */
                 for (i = 0; i < fc->server_list->nr_servers; i++) {
@@ -87,8 +88,8 @@ static bool afs_start_fs_iteration(struct afs_fs_cursor *fc,
 
                 /* Note that the callback promise is effectively broken */
                 write_seqlock(&vnode->cb_lock);
-                ASSERTCMP(cbi, ==, vnode->cb_interest);
-                vnode->cb_interest = NULL;
+                ASSERTCMP(cbi, ==, rcu_access_pointer(vnode->cb_interest));
+                rcu_assign_pointer(vnode->cb_interest, NULL);
                 if (test_and_clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags))
                         vnode->cb_break++;
                 write_sequnlock(&vnode->cb_lock);
@@ -417,7 +418,9 @@ selected_server:
         if (error < 0)
                 goto failed_set_error;
 
-        fc->cbi = afs_get_cb_interest(vnode->cb_interest);
+        fc->cbi = afs_get_cb_interest(
+                rcu_dereference_protected(vnode->cb_interest,
+                                          lockdep_is_held(&vnode->io_lock)));
 
         read_lock(&server->fs_lock);
         alist = rcu_dereference_protected(server->addresses,
@@ -487,12 +490,15 @@ failed:
 bool afs_select_current_fileserver(struct afs_fs_cursor *fc)
 {
         struct afs_vnode *vnode = fc->vnode;
-        struct afs_cb_interest *cbi = vnode->cb_interest;
+        struct afs_cb_interest *cbi;
         struct afs_addr_list *alist;
         int error = fc->ac.error;
 
         _enter("");
 
+        cbi = rcu_dereference_protected(vnode->cb_interest,
+                                        lockdep_is_held(&vnode->io_lock));
+
         switch (error) {
         case SHRT_MAX:
                 if (!cbi) {
@@ -501,7 +507,7 @@ bool afs_select_current_fileserver(struct afs_fs_cursor *fc)
                         return false;
                 }
 
-                fc->cbi = afs_get_cb_interest(vnode->cb_interest);
+                fc->cbi = afs_get_cb_interest(cbi);
 
                 read_lock(&cbi->server->fs_lock);
                 alist = rcu_dereference_protected(cbi->server->addresses,