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>

7 files changed, 100 insertions, 59 deletions

diff --git a/fs/afs/callback.c b/fs/afs/callback.c
index 4876079aa643..d441bef72163 100644
--- a/fs/afs/callback.c
+++ b/fs/afs/callback.c
@@ -94,15 +94,15 @@ int afs_register_server_cb_interest(struct afs_vnode *vnode,
         struct afs_server *server = entry->server;
 
 again:
-        if (vnode->cb_interest &&
-            likely(vnode->cb_interest == entry->cb_interest))
+        vcbi = rcu_dereference_protected(vnode->cb_interest,
+                                         lockdep_is_held(&vnode->io_lock));
+        if (vcbi && likely(vcbi == entry->cb_interest))
                 return 0;
 
         read_lock(&slist->lock);
         cbi = afs_get_cb_interest(entry->cb_interest);
         read_unlock(&slist->lock);
 
-        vcbi = vnode->cb_interest;
         if (vcbi) {
                 if (vcbi == cbi) {
                         afs_put_cb_interest(afs_v2net(vnode), cbi);
@@ -114,8 +114,9 @@ again:
                  */
                 if (cbi && vcbi->server == cbi->server) {
                         write_seqlock(&vnode->cb_lock);
-                        old = vnode->cb_interest;
-                        vnode->cb_interest = cbi;
+                        old = rcu_dereference_protected(vnode->cb_interest,
+                                                        lockdep_is_held(&vnode->cb_lock.lock));
+                        rcu_assign_pointer(vnode->cb_interest, cbi);
                         write_sequnlock(&vnode->cb_lock);
                         afs_put_cb_interest(afs_v2net(vnode), old);
                         return 0;
@@ -160,8 +161,9 @@ again:
          */
         write_seqlock(&vnode->cb_lock);
 
-        old = vnode->cb_interest;
-        vnode->cb_interest = cbi;
+        old = rcu_dereference_protected(vnode->cb_interest,
+                                        lockdep_is_held(&vnode->cb_lock.lock));
+        rcu_assign_pointer(vnode->cb_interest, cbi);
         vnode->cb_s_break = cbi->server->cb_s_break;
         vnode->cb_v_break = vnode->volume->cb_v_break;
         clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags);
@@ -191,10 +193,11 @@ void afs_put_cb_interest(struct afs_net *net, struct afs_cb_interest *cbi)
                                 vi = NULL;
 
                         write_unlock(&cbi->server->cb_break_lock);
-                        kfree(vi);
+                        if (vi)
+                                kfree_rcu(vi, rcu);
                         afs_put_server(net, cbi->server);
                 }
-                kfree(cbi);
+                kfree_rcu(cbi, rcu);
         }
 }
 
diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index f7344b045799..338c2260b0a0 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -638,11 +638,12 @@ static struct inode *afs_do_lookup(struct inode *dir, struct dentry *dentry,
                                    struct key *key)
 {
         struct afs_lookup_cookie *cookie;
-        struct afs_cb_interest *cbi = NULL;
+        struct afs_cb_interest *dcbi, *cbi = NULL;
         struct afs_super_info *as = dir->i_sb->s_fs_info;
         struct afs_status_cb *scb;
         struct afs_iget_data data;
         struct afs_fs_cursor fc;
+        struct afs_server *server;
         struct afs_vnode *dvnode = AFS_FS_I(dir);
         struct inode *inode = NULL;
         int ret, i;
@@ -658,10 +659,14 @@ static struct inode *afs_do_lookup(struct inode *dir, struct dentry *dentry,
         cookie->nr_fids = 1; /* slot 0 is saved for the fid we actually want */
 
         read_seqlock_excl(&dvnode->cb_lock);
-        if (dvnode->cb_interest &&
-            dvnode->cb_interest->server &&
-            test_bit(AFS_SERVER_FL_NO_IBULK, &dvnode->cb_interest->server->flags))
-                cookie->one_only = true;
+        dcbi = rcu_dereference_protected(dvnode->cb_interest,
+                                         lockdep_is_held(&dvnode->cb_lock.lock));
+        if (dcbi) {
+                server = dcbi->server;
+                if (server &&
+                    test_bit(AFS_SERVER_FL_NO_IBULK, &server->flags))
+                        cookie->one_only = true;
+        }
         read_sequnlock_excl(&dvnode->cb_lock);
 
         for (i = 0; i < 50; i++)
diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 5c95da7d5f3d..ba35b4824408 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -139,9 +139,10 @@ static int afs_inode_init_from_status(struct afs_vnode *vnode, struct key *key,
                 vnode->cb_expires_at = ktime_get_real_seconds();
         } else {
                 vnode->cb_expires_at = scb->callback.expires_at;
-                old_cbi = vnode->cb_interest;
+                old_cbi = rcu_dereference_protected(vnode->cb_interest,
+                                                    lockdep_is_held(&vnode->cb_lock.lock));
                 if (cbi != old_cbi)
-                        vnode->cb_interest = afs_get_cb_interest(cbi);
+                        rcu_assign_pointer(vnode->cb_interest, afs_get_cb_interest(cbi));
                 else
                         old_cbi = NULL;
                 set_bit(AFS_VNODE_CB_PROMISED, &vnode->flags);
@@ -245,9 +246,10 @@ static void afs_apply_callback(struct afs_fs_cursor *fc,
 
         if (!afs_cb_is_broken(cb_break, vnode, fc->cbi)) {
                 vnode->cb_expires_at    = cb->expires_at;
-                old = vnode->cb_interest;
+                old = rcu_dereference_protected(vnode->cb_interest,
+                                                lockdep_is_held(&vnode->cb_lock.lock));
                 if (old != fc->cbi) {
-                        vnode->cb_interest = afs_get_cb_interest(fc->cbi);
+                        rcu_assign_pointer(vnode->cb_interest, afs_get_cb_interest(fc->cbi));
                         afs_put_cb_interest(afs_v2net(vnode), old);
                 }
                 set_bit(AFS_VNODE_CB_PROMISED, &vnode->flags);
@@ -565,36 +567,46 @@ void afs_zap_data(struct afs_vnode *vnode)
  */
 bool afs_check_validity(struct afs_vnode *vnode)
 {
+        struct afs_cb_interest *cbi;
+        struct afs_server *server;
+        struct afs_volume *volume = vnode->volume;
         time64_t now = ktime_get_real_seconds();
         bool valid;
+        unsigned int cb_break, cb_s_break, cb_v_break;
+        int seq = 0;
 
-        /* Quickly check the callback state.  Ideally, we'd use read_seqbegin
-         * here, but we have no way to pass the net namespace to the RCU
-         * cleanup for the server record.
-         */
-        read_seqlock_excl(&vnode->cb_lock);
-
-        if (test_bit(AFS_VNODE_CB_PROMISED, &vnode->flags)) {
-                if (vnode->cb_s_break != vnode->cb_interest->server->cb_s_break ||
-                    vnode->cb_v_break != vnode->volume->cb_v_break) {
-                        vnode->cb_s_break = vnode->cb_interest->server->cb_s_break;
-                        vnode->cb_v_break = vnode->volume->cb_v_break;
-                        valid = false;
-                } else if (test_bit(AFS_VNODE_ZAP_DATA, &vnode->flags)) {
-                        valid = false;
-                } else if (vnode->cb_expires_at - 10 <= now) {
-                        valid = false;
-                } else {
+        do {
+                read_seqbegin_or_lock(&vnode->cb_lock, &seq);
+                cb_v_break = READ_ONCE(volume->cb_v_break);
+                cb_break = vnode->cb_break;
+
+                if (test_bit(AFS_VNODE_CB_PROMISED, &vnode->flags)) {
+                        cbi = rcu_dereference(vnode->cb_interest);
+                        server = rcu_dereference(cbi->server);
+                        cb_s_break = READ_ONCE(server->cb_s_break);
+
+                        if (vnode->cb_s_break != cb_s_break ||
+                            vnode->cb_v_break != cb_v_break) {
+                                vnode->cb_s_break = cb_s_break;
+                                vnode->cb_v_break = cb_v_break;
+                                valid = false;
+                        } else if (test_bit(AFS_VNODE_ZAP_DATA, &vnode->flags)) {
+                                valid = false;
+                        } else if (vnode->cb_expires_at - 10 <= now) {
+                                valid = false;
+                        } else {
+                                valid = true;
+                        }
+                } else if (test_bit(AFS_VNODE_DELETED, &vnode->flags)) {
                         valid = true;
+                } else {
+                        vnode->cb_v_break = cb_v_break;
+                        valid = false;
                 }
-        } else if (test_bit(AFS_VNODE_DELETED, &vnode->flags)) {
-                valid = true;
-        } else {
-                vnode->cb_v_break = vnode->volume->cb_v_break;
-                valid = false;
-        }
 
-        read_sequnlock_excl(&vnode->cb_lock);
+        } while (need_seqretry(&vnode->cb_lock, seq));
+
+        done_seqretry(&vnode->cb_lock, seq);
         return valid;
 }
 
@@ -616,7 +628,9 @@ int afs_validate(struct afs_vnode *vnode, struct key *key)
                vnode->fid.vid, vnode->fid.vnode, vnode->flags,
                key_serial(key));
 
+        rcu_read_lock();
         valid = afs_check_validity(vnode);
+        rcu_read_unlock();
 
         if (test_bit(AFS_VNODE_DELETED, &vnode->flags))
                 clear_nlink(&vnode->vfs_inode);
@@ -703,6 +717,7 @@ int afs_drop_inode(struct inode *inode)
  */
 void afs_evict_inode(struct inode *inode)
 {
+        struct afs_cb_interest *cbi;
         struct afs_vnode *vnode;
 
         vnode = AFS_FS_I(inode);
@@ -719,10 +734,14 @@ void afs_evict_inode(struct inode *inode)
         truncate_inode_pages_final(&inode->i_data);
         clear_inode(inode);
 
-        if (vnode->cb_interest) {
-                afs_put_cb_interest(afs_i2net(inode), vnode->cb_interest);
-                vnode->cb_interest = NULL;
+        write_seqlock(&vnode->cb_lock);
+        cbi = rcu_dereference_protected(vnode->cb_interest,
+                                        lockdep_is_held(&vnode->cb_lock.lock));
+        if (cbi) {
+                afs_put_cb_interest(afs_i2net(inode), cbi);
+                rcu_assign_pointer(vnode->cb_interest, NULL);
         }
+        write_sequnlock(&vnode->cb_lock);
 
         while (!list_empty(&vnode->wb_keys)) {
                 struct afs_wb_key *wbk = list_entry(vnode->wb_keys.next,
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 54688f6ca9e5..3dbb1e840dfd 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -554,7 +554,10 @@ struct afs_server {
 struct afs_vol_interest {
         struct hlist_node       srv_link;       /* Link in server->cb_volumes */
         struct hlist_head       cb_interests;   /* List of callback interests on the server */
-        afs_volid_t             vid;            /* Volume ID to match */
+        union {
+                struct rcu_head rcu;
+                afs_volid_t     vid;            /* Volume ID to match */
+        };
         unsigned int            usage;
 };
 
@@ -566,7 +569,10 @@ struct afs_cb_interest {
         struct afs_vol_interest *vol_interest;
         struct afs_server       *server;        /* Server on which this interest resides */
         struct super_block      *sb;            /* Superblock on which inodes reside */
-        afs_volid_t             vid;            /* Volume ID to match */
+        union {
+                struct rcu_head rcu;
+                afs_volid_t     vid;            /* Volume ID to match */
+        };
         refcount_t              usage;
 };
 
@@ -676,7 +682,7 @@ struct afs_vnode {
         afs_lock_type_t         lock_type : 8;
 
         /* outstanding callback notification on this file */
-        struct afs_cb_interest  *cb_interest;   /* Server on which this resides */
+        struct afs_cb_interest __rcu *cb_interest; /* Server on which this resides */
         unsigned int            cb_s_break;     /* Mass break counter on ->server */
         unsigned int            cb_v_break;     /* Mass break counter on ->volume */
         unsigned int            cb_break;       /* Break counter on vnode */
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,
diff --git a/fs/afs/security.c b/fs/afs/security.c
index 857f09d09ee9..5d8ece98561e 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -146,7 +146,7 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
                                 }
 
                                 if (afs_cb_is_broken(cb_break, vnode,
-                                                     vnode->cb_interest)) {
+                                                     rcu_dereference(vnode->cb_interest))) {
                                         changed = true;
                                         break;
                                 }
@@ -176,7 +176,7 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
                 }
         }
 
-        if (afs_cb_is_broken(cb_break, vnode, vnode->cb_interest))
+        if (afs_cb_is_broken(cb_break, vnode, rcu_dereference(vnode->cb_interest)))
                 goto someone_else_changed_it;
 
         /* We need a ref on any permits list we want to copy as we'll have to
@@ -253,14 +253,16 @@ found:
 
         kfree(new);
 
+        rcu_read_lock();
         spin_lock(&vnode->lock);
         zap = rcu_access_pointer(vnode->permit_cache);
-        if (!afs_cb_is_broken(cb_break, vnode, vnode->cb_interest) &&
+        if (!afs_cb_is_broken(cb_break, vnode, rcu_dereference(vnode->cb_interest)) &&
             zap == permits)
                 rcu_assign_pointer(vnode->permit_cache, replacement);
         else
                 zap = replacement;
         spin_unlock(&vnode->lock);
+        rcu_read_unlock();
         afs_put_permits(zap);
 out_put:
         afs_put_permits(permits);
diff --git a/fs/afs/super.c b/fs/afs/super.c
index a81c235f8c57..f76473ad7bbb 100644
--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -677,7 +677,7 @@ static struct inode *afs_alloc_inode(struct super_block *sb)
         vnode->volume           = NULL;
         vnode->lock_key         = NULL;
         vnode->permit_cache     = NULL;
-        vnode->cb_interest      = NULL;
+        RCU_INIT_POINTER(vnode->cb_interest, NULL);
 #ifdef CONFIG_AFS_FSCACHE
         vnode->cache            = NULL;
 #endif
@@ -707,7 +707,7 @@ static void afs_destroy_inode(struct inode *inode)
 
         _debug("DESTROY INODE %p", inode);
 
-        ASSERTCMP(vnode->cb_interest, ==, NULL);
+        ASSERTCMP(rcu_access_pointer(vnode->cb_interest), ==, NULL);
 
         atomic_dec(&afs_count_active_inodes);
 }