afs: Support RCU pathwalk

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

View File

@ -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));

View File

@ -303,6 +303,40 @@ someone_else_changed_it:
return;
}
static bool afs_check_permit_rcu(struct afs_vnode *vnode, struct key *key,
afs_access_t *_access)
{
const struct afs_permits *permits;
int i;
_enter("{%llx:%llu},%x",
vnode->fid.vid, vnode->fid.vnode, key_serial(key));
/* check the permits to see if we've got one yet */
if (key == vnode->volume->cell->anonymous_key) {
*_access = vnode->status.anon_access;
_leave(" = t [anon %x]", *_access);
return true;
}
permits = rcu_dereference(vnode->permit_cache);
if (permits) {
for (i = 0; i < permits->nr_permits; i++) {
if (permits->permits[i].key < key)
continue;
if (permits->permits[i].key > key)
break;
*_access = permits->permits[i].access;
_leave(" = %u [perm %x]", !permits->invalidated, *_access);
return !permits->invalidated;
}
}
_leave(" = f");
return false;
}
/*
* check with the fileserver to see if the directory or parent directory is
* permitted to be accessed with this authorisation, and if so, what access it
@ -369,33 +403,42 @@ int afs_permission(struct inode *inode, int mask)
struct afs_vnode *vnode = AFS_FS_I(inode);
afs_access_t uninitialized_var(access);
struct key *key;
int ret;
if (mask & MAY_NOT_BLOCK)
return -ECHILD;
int ret = 0;
_enter("{{%llx:%llu},%lx},%x,",
vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
key = afs_request_key(vnode->volume->cell);
if (IS_ERR(key)) {
_leave(" = %ld [key]", PTR_ERR(key));
return PTR_ERR(key);
if (mask & MAY_NOT_BLOCK) {
key = afs_request_key_rcu(vnode->volume->cell);
if (IS_ERR(key))
return -ECHILD;
ret = -ECHILD;
if (!afs_check_validity(vnode) ||
!afs_check_permit_rcu(vnode, key, &access))
goto error;
} else {
key = afs_request_key(vnode->volume->cell);
if (IS_ERR(key)) {
_leave(" = %ld [key]", PTR_ERR(key));
return PTR_ERR(key);
}
ret = afs_validate(vnode, key);
if (ret < 0)
goto error;
/* check the permits to see if we've got one yet */
ret = afs_check_permit(vnode, key, &access);
if (ret < 0)
goto error;
}
ret = afs_validate(vnode, key);
if (ret < 0)
goto error;
/* check the permits to see if we've got one yet */
ret = afs_check_permit(vnode, key, &access);
if (ret < 0)
goto error;
/* interpret the access mask */
_debug("REQ %x ACC %x on %s",
mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
ret = 0;
if (S_ISDIR(inode->i_mode)) {
if (mask & (MAY_EXEC | MAY_READ | MAY_CHDIR)) {
if (!(access & AFS_ACE_LOOKUP))