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vfs, afs, ext4: Make the inode hash table RCU searchable

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Make the inode hash table RCU searchable so that searches that want to
access or modify an inode without taking a ref on that inode can do so
without taking the inode hash table lock.

The main thing this requires is some RCU annotation on the list
manipulation operations.  Inodes are already freed by RCU in most cases.

Users of this interface must take care as the inode may be still under
construction or may be being torn down around them.

There are at least three instances where this can be of use:

 (1) Testing whether the inode number iunique() is going to return is
     currently unique (the iunique_lock is still held).

 (2) Ext4 date stamp updating.

 (3) AFS callback breaking.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
cc: linux-ext4@vger.kernel.org
cc: linux-afs@lists.infradead.org
This commit is contained in:
David Howells
2017-12-01 11:40:16 +00:00
parent 9cb1fd0efd
commit 3f19b2ab97
4 changed files with 130 additions and 41 deletions
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12
fs/afs/callback.c
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@@ -252,6 +252,7 @@ static void afs_break_one_callback(struct afs_server *server,
struct afs_vnode *vnode;
struct inode *inode;
rcu_read_lock();
read_lock(&server->cb_break_lock);
hlist_for_each_entry(vi, &server->cb_volumes, srv_link) {
if (vi->vid < fid->vid)
@@ -287,12 +288,16 @@ static void afs_break_one_callback(struct afs_server *server,
} else {
data.volume = NULL;
data.fid = *fid;
inode = ilookup5_nowait(cbi->sb, fid->vnode,
afs_iget5_test, &data);
/* See if we can find a matching inode - even an I_NEW
* inode needs to be marked as it can have its callback
* broken before we finish setting up the local inode.
*/
inode = find_inode_rcu(cbi->sb, fid->vnode,
afs_iget5_test, &data);
if (inode) {
vnode = AFS_FS_I(inode);
afs_break_callback(vnode, afs_cb_break_for_callback);
iput(inode);
} else {
trace_afs_cb_miss(fid, afs_cb_break_for_callback);
}
@@ -301,6 +306,7 @@ static void afs_break_one_callback(struct afs_server *server,
out:
read_unlock(&server->cb_break_lock);
rcu_read_unlock();
}
/*