![David Howells](/assets/img/avatar_default.png)
Simplify the way fscache cache objects retain their cookie. The way I implemented the cookie storage handling made synchronisation a pain (ie. the object state machine can't rely on the cookie actually still being there). Instead of the the object being detached from the cookie and the cookie being freed in __fscache_relinquish_cookie(), we defer both operations: (*) The detachment of the object from the list in the cookie now takes place in fscache_drop_object() and is thus governed by the object state machine (fscache_detach_from_cookie() has been removed). (*) The release of the cookie is now in fscache_object_destroy() - which is called by the cache backend just before it frees the object. This means that the fscache_cookie struct is now available to the cache all the way through from ->alloc_object() to ->drop_object() and ->put_object() - meaning that it's no longer necessary to take object->lock to guarantee access. However, __fscache_relinquish_cookie() doesn't wait for the object to go all the way through to destruction before letting the netfs proceed. That would massively slow down the netfs. Since __fscache_relinquish_cookie() leaves the cookie around, in must therefore break all attachments to the netfs - which includes ->def, ->netfs_data and any outstanding page read/writes. To handle this, struct fscache_cookie now has an n_active counter: (1) This starts off initialised to 1. (2) Any time the cache needs to get at the netfs data, it calls fscache_use_cookie() to increment it - if it is not zero. If it was zero, then access is not permitted. (3) When the cache has finished with the data, it calls fscache_unuse_cookie() to decrement it. This does a wake-up on it if it reaches 0. (4) __fscache_relinquish_cookie() decrements n_active and then waits for it to reach 0. The initialisation to 1 in step (1) ensures that we only get wake ups when we're trying to get rid of the cookie. This leaves __fscache_relinquish_cookie() a lot simpler. *** This fixes a problem in the current code whereby if fscache_invalidate() is followed sufficiently quickly by fscache_relinquish_cookie() then it is possible for __fscache_relinquish_cookie() to have detached the cookie from the object and cleared the pointer before a thread is dispatched to process the invalidation state in the object state machine. Since the pending write clearance was deferred to the invalidation state to make it asynchronous, we need to either wait in relinquishment for the stores tree to be cleared in the invalidation state or we need to handle the clearance in relinquishment. Further, if the relinquishment code does clear the tree, then the invalidation state need to make the clearance contingent on still having the cookie to hand (since that's where the tree is rooted) and we have to prevent the cookie from disappearing for the duration. This can lead to an oops like the following: BUG: unable to handle kernel NULL pointer dereference at 000000000000000c ... RIP: 0010:[<ffffffff8151023e>] _spin_lock+0xe/0x30 ... CR2: 000000000000000c ... ... Process kslowd002 (...) .... Call Trace: [<ffffffffa01c3278>] fscache_invalidate_writes+0x38/0xd0 [fscache] [<ffffffff810096f0>] ? __switch_to+0xd0/0x320 [<ffffffff8105e759>] ? find_busiest_queue+0x69/0x150 [<ffffffff8110ddd4>] ? slow_work_enqueue+0x104/0x180 [<ffffffffa01c1303>] fscache_object_slow_work_execute+0x5e3/0x9d0 [fscache] [<ffffffff81096b67>] ? bit_waitqueue+0x17/0xd0 [<ffffffff8110e233>] slow_work_execute+0x233/0x310 [<ffffffff8110e515>] slow_work_thread+0x205/0x360 [<ffffffff81096ca0>] ? autoremove_wake_function+0x0/0x40 [<ffffffff8110e310>] ? slow_work_thread+0x0/0x360 [<ffffffff81096936>] kthread+0x96/0xa0 [<ffffffff8100c0ca>] child_rip+0xa/0x20 [<ffffffff810968a0>] ? kthread+0x0/0xa0 [<ffffffff8100c0c0>] ? child_rip+0x0/0x20 The parameter to fscache_invalidate_writes() was object->cookie which is NULL. Signed-off-by: David Howells <dhowells@redhat.com> Tested-By: Milosz Tanski <milosz@adfin.com> Acked-by: Jeff Layton <jlayton@redhat.com>
561 lines
15 KiB
C
561 lines
15 KiB
C
/* netfs cookie management
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*
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* Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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* See Documentation/filesystems/caching/netfs-api.txt for more information on
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* the netfs API.
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*/
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#define FSCACHE_DEBUG_LEVEL COOKIE
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#include <linux/module.h>
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#include <linux/slab.h>
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#include "internal.h"
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struct kmem_cache *fscache_cookie_jar;
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static atomic_t fscache_object_debug_id = ATOMIC_INIT(0);
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static int fscache_acquire_non_index_cookie(struct fscache_cookie *cookie);
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static int fscache_alloc_object(struct fscache_cache *cache,
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struct fscache_cookie *cookie);
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static int fscache_attach_object(struct fscache_cookie *cookie,
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struct fscache_object *object);
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/*
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* initialise an cookie jar slab element prior to any use
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*/
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void fscache_cookie_init_once(void *_cookie)
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{
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struct fscache_cookie *cookie = _cookie;
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memset(cookie, 0, sizeof(*cookie));
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spin_lock_init(&cookie->lock);
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spin_lock_init(&cookie->stores_lock);
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INIT_HLIST_HEAD(&cookie->backing_objects);
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}
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/*
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* request a cookie to represent an object (index, datafile, xattr, etc)
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* - parent specifies the parent object
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* - the top level index cookie for each netfs is stored in the fscache_netfs
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* struct upon registration
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* - def points to the definition
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* - the netfs_data will be passed to the functions pointed to in *def
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* - all attached caches will be searched to see if they contain this object
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* - index objects aren't stored on disk until there's a dependent file that
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* needs storing
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* - other objects are stored in a selected cache immediately, and all the
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* indices forming the path to it are instantiated if necessary
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* - we never let on to the netfs about errors
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* - we may set a negative cookie pointer, but that's okay
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*/
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struct fscache_cookie *__fscache_acquire_cookie(
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struct fscache_cookie *parent,
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const struct fscache_cookie_def *def,
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void *netfs_data)
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{
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struct fscache_cookie *cookie;
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BUG_ON(!def);
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_enter("{%s},{%s},%p",
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parent ? (char *) parent->def->name : "<no-parent>",
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def->name, netfs_data);
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fscache_stat(&fscache_n_acquires);
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/* if there's no parent cookie, then we don't create one here either */
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if (!parent) {
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fscache_stat(&fscache_n_acquires_null);
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_leave(" [no parent]");
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return NULL;
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}
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/* validate the definition */
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BUG_ON(!def->get_key);
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BUG_ON(!def->name[0]);
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BUG_ON(def->type == FSCACHE_COOKIE_TYPE_INDEX &&
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parent->def->type != FSCACHE_COOKIE_TYPE_INDEX);
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/* allocate and initialise a cookie */
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cookie = kmem_cache_alloc(fscache_cookie_jar, GFP_KERNEL);
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if (!cookie) {
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fscache_stat(&fscache_n_acquires_oom);
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_leave(" [ENOMEM]");
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return NULL;
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}
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atomic_set(&cookie->usage, 1);
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atomic_set(&cookie->n_children, 0);
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/* We keep the active count elevated until relinquishment to prevent an
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* attempt to wake up every time the object operations queue quiesces.
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*/
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atomic_set(&cookie->n_active, 1);
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atomic_inc(&parent->usage);
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atomic_inc(&parent->n_children);
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cookie->def = def;
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cookie->parent = parent;
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cookie->netfs_data = netfs_data;
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cookie->flags = 0;
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/* radix tree insertion won't use the preallocation pool unless it's
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* told it may not wait */
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INIT_RADIX_TREE(&cookie->stores, GFP_NOFS & ~__GFP_WAIT);
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switch (cookie->def->type) {
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case FSCACHE_COOKIE_TYPE_INDEX:
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fscache_stat(&fscache_n_cookie_index);
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break;
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case FSCACHE_COOKIE_TYPE_DATAFILE:
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fscache_stat(&fscache_n_cookie_data);
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break;
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default:
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fscache_stat(&fscache_n_cookie_special);
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break;
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}
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/* if the object is an index then we need do nothing more here - we
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* create indices on disk when we need them as an index may exist in
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* multiple caches */
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if (cookie->def->type != FSCACHE_COOKIE_TYPE_INDEX) {
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if (fscache_acquire_non_index_cookie(cookie) < 0) {
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atomic_dec(&parent->n_children);
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__fscache_cookie_put(cookie);
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fscache_stat(&fscache_n_acquires_nobufs);
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_leave(" = NULL");
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return NULL;
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}
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}
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fscache_stat(&fscache_n_acquires_ok);
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_leave(" = %p", cookie);
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return cookie;
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}
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EXPORT_SYMBOL(__fscache_acquire_cookie);
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/*
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* acquire a non-index cookie
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* - this must make sure the index chain is instantiated and instantiate the
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* object representation too
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*/
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static int fscache_acquire_non_index_cookie(struct fscache_cookie *cookie)
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{
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struct fscache_object *object;
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struct fscache_cache *cache;
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uint64_t i_size;
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int ret;
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_enter("");
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cookie->flags = 1 << FSCACHE_COOKIE_UNAVAILABLE;
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/* now we need to see whether the backing objects for this cookie yet
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* exist, if not there'll be nothing to search */
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down_read(&fscache_addremove_sem);
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if (list_empty(&fscache_cache_list)) {
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up_read(&fscache_addremove_sem);
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_leave(" = 0 [no caches]");
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return 0;
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}
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/* select a cache in which to store the object */
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cache = fscache_select_cache_for_object(cookie->parent);
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if (!cache) {
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up_read(&fscache_addremove_sem);
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fscache_stat(&fscache_n_acquires_no_cache);
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_leave(" = -ENOMEDIUM [no cache]");
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return -ENOMEDIUM;
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}
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_debug("cache %s", cache->tag->name);
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cookie->flags =
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(1 << FSCACHE_COOKIE_LOOKING_UP) |
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(1 << FSCACHE_COOKIE_NO_DATA_YET);
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/* ask the cache to allocate objects for this cookie and its parent
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* chain */
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ret = fscache_alloc_object(cache, cookie);
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if (ret < 0) {
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up_read(&fscache_addremove_sem);
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_leave(" = %d", ret);
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return ret;
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}
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/* pass on how big the object we're caching is supposed to be */
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cookie->def->get_attr(cookie->netfs_data, &i_size);
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spin_lock(&cookie->lock);
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if (hlist_empty(&cookie->backing_objects)) {
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spin_unlock(&cookie->lock);
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goto unavailable;
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}
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object = hlist_entry(cookie->backing_objects.first,
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struct fscache_object, cookie_link);
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fscache_set_store_limit(object, i_size);
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/* initiate the process of looking up all the objects in the chain
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* (done by fscache_initialise_object()) */
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fscache_raise_event(object, FSCACHE_OBJECT_EV_NEW_CHILD);
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spin_unlock(&cookie->lock);
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/* we may be required to wait for lookup to complete at this point */
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if (!fscache_defer_lookup) {
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_debug("non-deferred lookup %p", &cookie->flags);
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wait_on_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP,
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fscache_wait_bit, TASK_UNINTERRUPTIBLE);
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_debug("complete");
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if (test_bit(FSCACHE_COOKIE_UNAVAILABLE, &cookie->flags))
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goto unavailable;
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}
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up_read(&fscache_addremove_sem);
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_leave(" = 0 [deferred]");
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return 0;
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unavailable:
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up_read(&fscache_addremove_sem);
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_leave(" = -ENOBUFS");
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return -ENOBUFS;
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}
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/*
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* recursively allocate cache object records for a cookie/cache combination
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* - caller must be holding the addremove sem
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*/
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static int fscache_alloc_object(struct fscache_cache *cache,
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struct fscache_cookie *cookie)
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{
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struct fscache_object *object;
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int ret;
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_enter("%p,%p{%s}", cache, cookie, cookie->def->name);
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spin_lock(&cookie->lock);
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hlist_for_each_entry(object, &cookie->backing_objects,
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cookie_link) {
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if (object->cache == cache)
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goto object_already_extant;
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}
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spin_unlock(&cookie->lock);
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/* ask the cache to allocate an object (we may end up with duplicate
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* objects at this stage, but we sort that out later) */
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fscache_stat(&fscache_n_cop_alloc_object);
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object = cache->ops->alloc_object(cache, cookie);
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fscache_stat_d(&fscache_n_cop_alloc_object);
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if (IS_ERR(object)) {
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fscache_stat(&fscache_n_object_no_alloc);
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ret = PTR_ERR(object);
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goto error;
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}
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fscache_stat(&fscache_n_object_alloc);
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object->debug_id = atomic_inc_return(&fscache_object_debug_id);
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_debug("ALLOC OBJ%x: %s {%lx}",
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object->debug_id, cookie->def->name, object->events);
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ret = fscache_alloc_object(cache, cookie->parent);
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if (ret < 0)
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goto error_put;
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/* only attach if we managed to allocate all we needed, otherwise
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* discard the object we just allocated and instead use the one
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* attached to the cookie */
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if (fscache_attach_object(cookie, object) < 0) {
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fscache_stat(&fscache_n_cop_put_object);
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cache->ops->put_object(object);
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fscache_stat_d(&fscache_n_cop_put_object);
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}
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_leave(" = 0");
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return 0;
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object_already_extant:
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ret = -ENOBUFS;
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if (fscache_object_is_dead(object)) {
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spin_unlock(&cookie->lock);
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goto error;
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}
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spin_unlock(&cookie->lock);
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_leave(" = 0 [found]");
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return 0;
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error_put:
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fscache_stat(&fscache_n_cop_put_object);
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cache->ops->put_object(object);
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fscache_stat_d(&fscache_n_cop_put_object);
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error:
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_leave(" = %d", ret);
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return ret;
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}
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/*
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* attach a cache object to a cookie
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*/
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static int fscache_attach_object(struct fscache_cookie *cookie,
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struct fscache_object *object)
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{
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struct fscache_object *p;
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struct fscache_cache *cache = object->cache;
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int ret;
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_enter("{%s},{OBJ%x}", cookie->def->name, object->debug_id);
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spin_lock(&cookie->lock);
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/* there may be multiple initial creations of this object, but we only
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* want one */
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ret = -EEXIST;
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hlist_for_each_entry(p, &cookie->backing_objects, cookie_link) {
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if (p->cache == object->cache) {
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if (fscache_object_is_dying(p))
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ret = -ENOBUFS;
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goto cant_attach_object;
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}
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}
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/* pin the parent object */
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spin_lock_nested(&cookie->parent->lock, 1);
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hlist_for_each_entry(p, &cookie->parent->backing_objects,
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cookie_link) {
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if (p->cache == object->cache) {
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if (fscache_object_is_dying(p)) {
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ret = -ENOBUFS;
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spin_unlock(&cookie->parent->lock);
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goto cant_attach_object;
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}
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object->parent = p;
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spin_lock(&p->lock);
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p->n_children++;
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spin_unlock(&p->lock);
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break;
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}
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}
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spin_unlock(&cookie->parent->lock);
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/* attach to the cache's object list */
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if (list_empty(&object->cache_link)) {
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spin_lock(&cache->object_list_lock);
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list_add(&object->cache_link, &cache->object_list);
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spin_unlock(&cache->object_list_lock);
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}
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/* attach to the cookie */
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object->cookie = cookie;
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atomic_inc(&cookie->usage);
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hlist_add_head(&object->cookie_link, &cookie->backing_objects);
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fscache_objlist_add(object);
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ret = 0;
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cant_attach_object:
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spin_unlock(&cookie->lock);
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_leave(" = %d", ret);
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return ret;
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}
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/*
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* Invalidate an object. Callable with spinlocks held.
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*/
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void __fscache_invalidate(struct fscache_cookie *cookie)
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{
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struct fscache_object *object;
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_enter("{%s}", cookie->def->name);
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fscache_stat(&fscache_n_invalidates);
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/* Only permit invalidation of data files. Invalidating an index will
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* require the caller to release all its attachments to the tree rooted
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* there, and if it's doing that, it may as well just retire the
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* cookie.
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*/
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ASSERTCMP(cookie->def->type, ==, FSCACHE_COOKIE_TYPE_DATAFILE);
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/* We will be updating the cookie too. */
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BUG_ON(!cookie->def->get_aux);
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/* If there's an object, we tell the object state machine to handle the
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* invalidation on our behalf, otherwise there's nothing to do.
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*/
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if (!hlist_empty(&cookie->backing_objects)) {
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spin_lock(&cookie->lock);
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if (!hlist_empty(&cookie->backing_objects) &&
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!test_and_set_bit(FSCACHE_COOKIE_INVALIDATING,
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&cookie->flags)) {
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object = hlist_entry(cookie->backing_objects.first,
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struct fscache_object,
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cookie_link);
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if (fscache_object_is_live(object))
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fscache_raise_event(
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object, FSCACHE_OBJECT_EV_INVALIDATE);
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}
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spin_unlock(&cookie->lock);
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}
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_leave("");
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}
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EXPORT_SYMBOL(__fscache_invalidate);
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/*
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* Wait for object invalidation to complete.
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*/
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void __fscache_wait_on_invalidate(struct fscache_cookie *cookie)
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{
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_enter("%p", cookie);
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wait_on_bit(&cookie->flags, FSCACHE_COOKIE_INVALIDATING,
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fscache_wait_bit_interruptible,
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TASK_UNINTERRUPTIBLE);
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_leave("");
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}
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EXPORT_SYMBOL(__fscache_wait_on_invalidate);
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/*
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* update the index entries backing a cookie
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*/
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void __fscache_update_cookie(struct fscache_cookie *cookie)
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{
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struct fscache_object *object;
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fscache_stat(&fscache_n_updates);
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if (!cookie) {
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fscache_stat(&fscache_n_updates_null);
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_leave(" [no cookie]");
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return;
|
|
}
|
|
|
|
_enter("{%s}", cookie->def->name);
|
|
|
|
BUG_ON(!cookie->def->get_aux);
|
|
|
|
spin_lock(&cookie->lock);
|
|
|
|
/* update the index entry on disk in each cache backing this cookie */
|
|
hlist_for_each_entry(object,
|
|
&cookie->backing_objects, cookie_link) {
|
|
fscache_raise_event(object, FSCACHE_OBJECT_EV_UPDATE);
|
|
}
|
|
|
|
spin_unlock(&cookie->lock);
|
|
_leave("");
|
|
}
|
|
EXPORT_SYMBOL(__fscache_update_cookie);
|
|
|
|
/*
|
|
* release a cookie back to the cache
|
|
* - the object will be marked as recyclable on disk if retire is true
|
|
* - all dependents of this cookie must have already been unregistered
|
|
* (indices/files/pages)
|
|
*/
|
|
void __fscache_relinquish_cookie(struct fscache_cookie *cookie, int retire)
|
|
{
|
|
struct fscache_object *object;
|
|
|
|
fscache_stat(&fscache_n_relinquishes);
|
|
if (retire)
|
|
fscache_stat(&fscache_n_relinquishes_retire);
|
|
|
|
if (!cookie) {
|
|
fscache_stat(&fscache_n_relinquishes_null);
|
|
_leave(" [no cookie]");
|
|
return;
|
|
}
|
|
|
|
_enter("%p{%s,%p,%d},%d",
|
|
cookie, cookie->def->name, cookie->netfs_data,
|
|
atomic_read(&cookie->n_active), retire);
|
|
|
|
ASSERTCMP(atomic_read(&cookie->n_active), >, 0);
|
|
|
|
if (atomic_read(&cookie->n_children) != 0) {
|
|
printk(KERN_ERR "FS-Cache: Cookie '%s' still has children\n",
|
|
cookie->def->name);
|
|
BUG();
|
|
}
|
|
|
|
/* No further netfs-accessing operations on this cookie permitted */
|
|
set_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags);
|
|
if (retire)
|
|
set_bit(FSCACHE_COOKIE_RETIRED, &cookie->flags);
|
|
|
|
spin_lock(&cookie->lock);
|
|
hlist_for_each_entry(object, &cookie->backing_objects, cookie_link) {
|
|
fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
|
|
}
|
|
spin_unlock(&cookie->lock);
|
|
|
|
/* Wait for cessation of activity requiring access to the netfs (when
|
|
* n_active reaches 0).
|
|
*/
|
|
if (!atomic_dec_and_test(&cookie->n_active))
|
|
wait_on_atomic_t(&cookie->n_active, fscache_wait_atomic_t,
|
|
TASK_UNINTERRUPTIBLE);
|
|
|
|
/* Clear pointers back to the netfs */
|
|
cookie->netfs_data = NULL;
|
|
cookie->def = NULL;
|
|
BUG_ON(cookie->stores.rnode);
|
|
|
|
if (cookie->parent) {
|
|
ASSERTCMP(atomic_read(&cookie->parent->usage), >, 0);
|
|
ASSERTCMP(atomic_read(&cookie->parent->n_children), >, 0);
|
|
atomic_dec(&cookie->parent->n_children);
|
|
}
|
|
|
|
/* Dispose of the netfs's link to the cookie */
|
|
ASSERTCMP(atomic_read(&cookie->usage), >, 0);
|
|
fscache_cookie_put(cookie);
|
|
|
|
_leave("");
|
|
}
|
|
EXPORT_SYMBOL(__fscache_relinquish_cookie);
|
|
|
|
/*
|
|
* destroy a cookie
|
|
*/
|
|
void __fscache_cookie_put(struct fscache_cookie *cookie)
|
|
{
|
|
struct fscache_cookie *parent;
|
|
|
|
_enter("%p", cookie);
|
|
|
|
for (;;) {
|
|
_debug("FREE COOKIE %p", cookie);
|
|
parent = cookie->parent;
|
|
BUG_ON(!hlist_empty(&cookie->backing_objects));
|
|
kmem_cache_free(fscache_cookie_jar, cookie);
|
|
|
|
if (!parent)
|
|
break;
|
|
|
|
cookie = parent;
|
|
BUG_ON(atomic_read(&cookie->usage) <= 0);
|
|
if (!atomic_dec_and_test(&cookie->usage))
|
|
break;
|
|
}
|
|
|
|
_leave("");
|
|
}
|