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afs: Support RCU pathwalk

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Make afs_permission() and afs_d_revalidate() do initial checks in RCU-mode
pathwalk to reduce latency in pathwalk elements that get done multiple
times.  We don't need to query the server unless we've received a
notification from it that something has changed or the callback has
expired.

This requires that we can request a key and check permits under RCU
conditions if we need to.

Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
David Howells
2019-05-20 08:48:46 +01:00
parent 8b6a666a97
commit a0753c2900
2 changed files with 113 additions and 18 deletions
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54
fs/afs/dir.c
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@@ -965,6 +965,58 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
return d;
}
/*
* Check the validity of a dentry under RCU conditions.
*/
static int afs_d_revalidate_rcu(struct dentry *dentry)
{
struct afs_vnode *dvnode, *vnode;
struct dentry *parent;
struct inode *dir, *inode;
long dir_version, de_version;
_enter("%p", dentry);
/* Check the parent directory is still valid first. */
parent = READ_ONCE(dentry->d_parent);
dir = d_inode_rcu(parent);
if (!dir)
return -ECHILD;
dvnode = AFS_FS_I(dir);
if (test_bit(AFS_VNODE_DELETED, &dvnode->flags))
return -ECHILD;
if (!afs_check_validity(dvnode))
return -ECHILD;
/* We only need to invalidate a dentry if the server's copy changed
* behind our back. If we made the change, it's no problem. Note that
* on a 32-bit system, we only have 32 bits in the dentry to store the
* version.
*/
dir_version = (long)READ_ONCE(dvnode->status.data_version);
de_version = (long)READ_ONCE(dentry->d_fsdata);
if (de_version != dir_version) {
dir_version = (long)READ_ONCE(dvnode->invalid_before);
if (de_version - dir_version < 0)
return -ECHILD;
}
/* Check to see if the vnode referred to by the dentry still
* has a callback.
*/
if (d_really_is_positive(dentry)) {
inode = d_inode_rcu(dentry);
if (inode) {
vnode = AFS_FS_I(inode);
if (!afs_check_validity(vnode))
return -ECHILD;
}
}
return 1; /* Still valid */
}
/*
* check that a dentry lookup hit has found a valid entry
* - NOTE! the hit can be a negative hit too, so we can't assume we have an
@@ -982,7 +1034,7 @@ static int afs_d_revalidate(struct dentry *dentry, unsigned int flags)
int ret;
if (flags & LOOKUP_RCU)
return -ECHILD;
return afs_d_revalidate_rcu(dentry);
if (d_really_is_positive(dentry)) {
vnode = AFS_FS_I(d_inode(dentry));