linux/fs/afs/callback.c
David Howells 4fe6a94682 afs: Try to avoid taking RCU read lock when checking vnode validity
Try to avoid taking the RCU read lock when checking the validity of a
vnode's callback state.  The only thing it's needed for is to pin the
parent volume's server list whilst we search it to find the record of the
server we're currently using to see if it has been reinitialised (ie. it
sent us a CB.InitCallBackState* RPC).

Do this by the following means:

 (1) Keep an additional per-cell counter (fs_s_break) that's incremented
     each time any of the fileservers in the cell reinitialises.

     Since the new counter can be accessed without RCU from the vnode, we
     can check that first - and only if it differs, get the RCU read lock
     and check the volume's server list.

 (2) Replace afs_get_s_break_rcu() with afs_check_server_good() which now
     indicates whether the callback promise is still expected to be present
     on the server.  This does the checks as described in (1).

 (3) Restructure afs_check_validity() to take account of the change in (2).

     We can also get rid of the valid variable and just use the need_clear
     variable with the addition of the afs_cb_break_no_promise reason.

 (4) afs_check_validity() probably shouldn't be altering vnode->cb_v_break
     and vnode->cb_s_break when it doesn't have cb_lock exclusively locked.

     Move the change to vnode->cb_v_break to __afs_break_callback().

     Delegate the change to vnode->cb_s_break to afs_select_fileserver()
     and set vnode->cb_fs_s_break there also.

 (5) afs_validate() no longer needs to get the RCU read lock around its
     call to afs_check_validity() - and can skip the call entirely if we
     don't have a promise.

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Markus Suvanto <markus.suvanto@gmail.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/163111669583.283156.1397603105683094563.stgit@warthog.procyon.org.uk/
2021-09-13 09:10:39 +01:00

229 lines
5.9 KiB
C

/*
* Copyright (c) 2002, 2007 Red Hat, Inc. All rights reserved.
*
* This software may be freely redistributed under the terms of the
* GNU General Public License.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* Authors: David Woodhouse <dwmw2@infradead.org>
* David Howells <dhowells@redhat.com>
*
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/circ_buf.h>
#include <linux/sched.h>
#include "internal.h"
/*
* Handle invalidation of an mmap'd file. We invalidate all the PTEs referring
* to the pages in this file's pagecache, forcing the kernel to go through
* ->fault() or ->page_mkwrite() - at which point we can handle invalidation
* more fully.
*/
void afs_invalidate_mmap_work(struct work_struct *work)
{
struct afs_vnode *vnode = container_of(work, struct afs_vnode, cb_work);
unmap_mapping_pages(vnode->vfs_inode.i_mapping, 0, 0, false);
}
void afs_server_init_callback_work(struct work_struct *work)
{
struct afs_server *server = container_of(work, struct afs_server, initcb_work);
struct afs_vnode *vnode;
struct afs_cell *cell = server->cell;
down_read(&cell->fs_open_mmaps_lock);
list_for_each_entry(vnode, &cell->fs_open_mmaps, cb_mmap_link) {
if (vnode->cb_server == server) {
clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags);
queue_work(system_unbound_wq, &vnode->cb_work);
}
}
up_read(&cell->fs_open_mmaps_lock);
}
/*
* Allow the fileserver to request callback state (re-)initialisation.
* Unfortunately, UUIDs are not guaranteed unique.
*/
void afs_init_callback_state(struct afs_server *server)
{
rcu_read_lock();
do {
server->cb_s_break++;
atomic_inc(&server->cell->fs_s_break);
if (!list_empty(&server->cell->fs_open_mmaps))
queue_work(system_unbound_wq, &server->initcb_work);
} while ((server = rcu_dereference(server->uuid_next)));
rcu_read_unlock();
}
/*
* actually break a callback
*/
void __afs_break_callback(struct afs_vnode *vnode, enum afs_cb_break_reason reason)
{
_enter("");
clear_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags);
if (test_and_clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags)) {
vnode->cb_break++;
vnode->cb_v_break = vnode->volume->cb_v_break;
afs_clear_permits(vnode);
if (vnode->lock_state == AFS_VNODE_LOCK_WAITING_FOR_CB)
afs_lock_may_be_available(vnode);
if (reason != afs_cb_break_for_deleted &&
vnode->status.type == AFS_FTYPE_FILE &&
atomic_read(&vnode->cb_nr_mmap))
queue_work(system_unbound_wq, &vnode->cb_work);
trace_afs_cb_break(&vnode->fid, vnode->cb_break, reason, true);
} else {
trace_afs_cb_break(&vnode->fid, vnode->cb_break, reason, false);
}
}
void afs_break_callback(struct afs_vnode *vnode, enum afs_cb_break_reason reason)
{
write_seqlock(&vnode->cb_lock);
__afs_break_callback(vnode, reason);
write_sequnlock(&vnode->cb_lock);
}
/*
* Look up a volume by volume ID under RCU conditions.
*/
static struct afs_volume *afs_lookup_volume_rcu(struct afs_cell *cell,
afs_volid_t vid)
{
struct afs_volume *volume = NULL;
struct rb_node *p;
int seq = 0;
do {
/* Unfortunately, rbtree walking doesn't give reliable results
* under just the RCU read lock, so we have to check for
* changes.
*/
read_seqbegin_or_lock(&cell->volume_lock, &seq);
p = rcu_dereference_raw(cell->volumes.rb_node);
while (p) {
volume = rb_entry(p, struct afs_volume, cell_node);
if (volume->vid < vid)
p = rcu_dereference_raw(p->rb_left);
else if (volume->vid > vid)
p = rcu_dereference_raw(p->rb_right);
else
break;
volume = NULL;
}
} while (need_seqretry(&cell->volume_lock, seq));
done_seqretry(&cell->volume_lock, seq);
return volume;
}
/*
* allow the fileserver to explicitly break one callback
* - happens when
* - the backing file is changed
* - a lock is released
*/
static void afs_break_one_callback(struct afs_volume *volume,
struct afs_fid *fid)
{
struct super_block *sb;
struct afs_vnode *vnode;
struct inode *inode;
if (fid->vnode == 0 && fid->unique == 0) {
/* The callback break applies to an entire volume. */
write_lock(&volume->cb_v_break_lock);
volume->cb_v_break++;
trace_afs_cb_break(fid, volume->cb_v_break,
afs_cb_break_for_volume_callback, false);
write_unlock(&volume->cb_v_break_lock);
return;
}
/* 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.
*/
sb = rcu_dereference(volume->sb);
if (!sb)
return;
inode = find_inode_rcu(sb, fid->vnode, afs_ilookup5_test_by_fid, fid);
if (inode) {
vnode = AFS_FS_I(inode);
afs_break_callback(vnode, afs_cb_break_for_callback);
} else {
trace_afs_cb_miss(fid, afs_cb_break_for_callback);
}
}
static void afs_break_some_callbacks(struct afs_server *server,
struct afs_callback_break *cbb,
size_t *_count)
{
struct afs_callback_break *residue = cbb;
struct afs_volume *volume;
afs_volid_t vid = cbb->fid.vid;
size_t i;
volume = afs_lookup_volume_rcu(server->cell, vid);
/* TODO: Find all matching volumes if we couldn't match the server and
* break them anyway.
*/
for (i = *_count; i > 0; cbb++, i--) {
if (cbb->fid.vid == vid) {
_debug("- Fid { vl=%08llx n=%llu u=%u }",
cbb->fid.vid,
cbb->fid.vnode,
cbb->fid.unique);
--*_count;
if (volume)
afs_break_one_callback(volume, &cbb->fid);
} else {
*residue++ = *cbb;
}
}
}
/*
* allow the fileserver to break callback promises
*/
void afs_break_callbacks(struct afs_server *server, size_t count,
struct afs_callback_break *callbacks)
{
_enter("%p,%zu,", server, count);
ASSERT(server != NULL);
rcu_read_lock();
while (count > 0)
afs_break_some_callbacks(server, callbacks, &count);
rcu_read_unlock();
return;
}