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![David Howells](/assets/img/avatar_default.png)
Count the data storage objects that are currently allocated in a cache. This is used to pin certain cache structures until cache withdrawal is complete. Three helpers are provided to manage and make use of the count: (1) void fscache_count_object(struct fscache_cache *cache); This should be called by the cache backend to note that an object has been allocated and attached to the cache. (2) void fscache_uncount_object(struct fscache_cache *cache); This should be called by the backend to note that an object has been destroyed. This sends a wakeup event that allows cache withdrawal to proceed if it was waiting for that object. (3) void fscache_wait_for_objects(struct fscache_cache *cache); This can be used by the backend to wait for all outstanding cache object to be destroyed. Each cache's counter is displayed as part of /proc/fs/fscache/caches. Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819608594.215744.1812706538117388252.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906911646.143852.168184059935530127.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967111846.1823006.9868154941573671255.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021516219.640689.4934796654308958158.stgit@warthog.procyon.org.uk/ # v4
428 lines
12 KiB
C
428 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* FS-Cache cache handling
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*
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* Copyright (C) 2021 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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#define FSCACHE_DEBUG_LEVEL CACHE
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#include <linux/export.h>
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#include <linux/slab.h>
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#include "internal.h"
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static LIST_HEAD(fscache_caches);
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DECLARE_RWSEM(fscache_addremove_sem);
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EXPORT_SYMBOL(fscache_addremove_sem);
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DECLARE_WAIT_QUEUE_HEAD(fscache_clearance_waiters);
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EXPORT_SYMBOL(fscache_clearance_waiters);
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static atomic_t fscache_cache_debug_id;
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/*
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* Allocate a cache cookie.
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*/
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static struct fscache_cache *fscache_alloc_cache(const char *name)
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{
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struct fscache_cache *cache;
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cache = kzalloc(sizeof(*cache), GFP_KERNEL);
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if (cache) {
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if (name) {
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cache->name = kstrdup(name, GFP_KERNEL);
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if (!cache->name) {
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kfree(cache);
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return NULL;
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}
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}
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refcount_set(&cache->ref, 1);
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INIT_LIST_HEAD(&cache->cache_link);
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cache->debug_id = atomic_inc_return(&fscache_cache_debug_id);
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}
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return cache;
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}
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static bool fscache_get_cache_maybe(struct fscache_cache *cache,
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enum fscache_cache_trace where)
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{
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bool success;
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int ref;
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success = __refcount_inc_not_zero(&cache->ref, &ref);
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if (success)
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trace_fscache_cache(cache->debug_id, ref + 1, where);
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return success;
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}
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/*
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* Look up a cache cookie.
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*/
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struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache)
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{
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struct fscache_cache *candidate, *cache, *unnamed = NULL;
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/* firstly check for the existence of the cache under read lock */
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down_read(&fscache_addremove_sem);
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list_for_each_entry(cache, &fscache_caches, cache_link) {
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if (cache->name && name && strcmp(cache->name, name) == 0 &&
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
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goto got_cache_r;
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if (!cache->name && !name &&
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
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goto got_cache_r;
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}
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if (!name) {
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list_for_each_entry(cache, &fscache_caches, cache_link) {
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if (cache->name &&
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
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goto got_cache_r;
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}
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}
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up_read(&fscache_addremove_sem);
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/* the cache does not exist - create a candidate */
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candidate = fscache_alloc_cache(name);
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if (!candidate)
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return ERR_PTR(-ENOMEM);
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/* write lock, search again and add if still not present */
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down_write(&fscache_addremove_sem);
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list_for_each_entry(cache, &fscache_caches, cache_link) {
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if (cache->name && name && strcmp(cache->name, name) == 0 &&
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
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goto got_cache_w;
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if (!cache->name) {
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unnamed = cache;
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if (!name &&
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
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goto got_cache_w;
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}
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}
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if (unnamed && is_cache &&
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fscache_get_cache_maybe(unnamed, fscache_cache_get_acquire))
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goto use_unnamed_cache;
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if (!name) {
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list_for_each_entry(cache, &fscache_caches, cache_link) {
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if (cache->name &&
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fscache_get_cache_maybe(cache, fscache_cache_get_acquire))
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goto got_cache_w;
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}
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}
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list_add_tail(&candidate->cache_link, &fscache_caches);
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trace_fscache_cache(candidate->debug_id,
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refcount_read(&candidate->ref),
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fscache_cache_new_acquire);
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up_write(&fscache_addremove_sem);
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return candidate;
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got_cache_r:
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up_read(&fscache_addremove_sem);
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return cache;
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use_unnamed_cache:
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cache = unnamed;
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cache->name = candidate->name;
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candidate->name = NULL;
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got_cache_w:
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up_write(&fscache_addremove_sem);
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kfree(candidate->name);
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kfree(candidate);
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return cache;
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}
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/**
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* fscache_acquire_cache - Acquire a cache-level cookie.
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* @name: The name of the cache.
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*
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* Get a cookie to represent an actual cache. If a name is given and there is
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* a nameless cache record available, this will acquire that and set its name,
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* directing all the volumes using it to this cache.
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*
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* The cache will be switched over to the preparing state if not currently in
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* use, otherwise -EBUSY will be returned.
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*/
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struct fscache_cache *fscache_acquire_cache(const char *name)
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{
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struct fscache_cache *cache;
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ASSERT(name);
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cache = fscache_lookup_cache(name, true);
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if (IS_ERR(cache))
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return cache;
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if (!fscache_set_cache_state_maybe(cache,
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FSCACHE_CACHE_IS_NOT_PRESENT,
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FSCACHE_CACHE_IS_PREPARING)) {
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pr_warn("Cache tag %s in use\n", name);
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fscache_put_cache(cache, fscache_cache_put_cache);
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return ERR_PTR(-EBUSY);
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}
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return cache;
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}
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EXPORT_SYMBOL(fscache_acquire_cache);
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/**
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* fscache_put_cache - Release a cache-level cookie.
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* @cache: The cache cookie to be released
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* @where: An indication of where the release happened
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*
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* Release the caller's reference on a cache-level cookie. The @where
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* indication should give information about the circumstances in which the call
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* occurs and will be logged through a tracepoint.
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*/
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void fscache_put_cache(struct fscache_cache *cache,
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enum fscache_cache_trace where)
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{
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unsigned int debug_id = cache->debug_id;
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bool zero;
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int ref;
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if (IS_ERR_OR_NULL(cache))
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return;
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zero = __refcount_dec_and_test(&cache->ref, &ref);
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trace_fscache_cache(debug_id, ref - 1, where);
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if (zero) {
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down_write(&fscache_addremove_sem);
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list_del_init(&cache->cache_link);
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up_write(&fscache_addremove_sem);
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kfree(cache->name);
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kfree(cache);
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}
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}
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/**
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* fscache_relinquish_cache - Reset cache state and release cookie
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* @cache: The cache cookie to be released
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*
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* Reset the state of a cache and release the caller's reference on a cache
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* cookie.
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*/
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void fscache_relinquish_cache(struct fscache_cache *cache)
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{
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enum fscache_cache_trace where =
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(cache->state == FSCACHE_CACHE_IS_PREPARING) ?
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fscache_cache_put_prep_failed :
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fscache_cache_put_relinquish;
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cache->ops = NULL;
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cache->cache_priv = NULL;
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smp_store_release(&cache->state, FSCACHE_CACHE_IS_NOT_PRESENT);
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fscache_put_cache(cache, where);
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}
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EXPORT_SYMBOL(fscache_relinquish_cache);
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/**
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* fscache_add_cache - Declare a cache as being open for business
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* @cache: The cache-level cookie representing the cache
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* @ops: Table of cache operations to use
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* @cache_priv: Private data for the cache record
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*
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* Add a cache to the system, making it available for netfs's to use.
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*
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* See Documentation/filesystems/caching/backend-api.rst for a complete
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* description.
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*/
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int fscache_add_cache(struct fscache_cache *cache,
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const struct fscache_cache_ops *ops,
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void *cache_priv)
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{
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int n_accesses;
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_enter("{%s,%s}", ops->name, cache->name);
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BUG_ON(fscache_cache_state(cache) != FSCACHE_CACHE_IS_PREPARING);
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/* Get a ref on the cache cookie and keep its n_accesses counter raised
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* by 1 to prevent wakeups from transitioning it to 0 until we're
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* withdrawing caching services from it.
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*/
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n_accesses = atomic_inc_return(&cache->n_accesses);
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trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref),
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n_accesses, fscache_access_cache_pin);
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down_write(&fscache_addremove_sem);
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cache->ops = ops;
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cache->cache_priv = cache_priv;
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fscache_set_cache_state(cache, FSCACHE_CACHE_IS_ACTIVE);
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up_write(&fscache_addremove_sem);
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pr_notice("Cache \"%s\" added (type %s)\n", cache->name, ops->name);
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_leave(" = 0 [%s]", cache->name);
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return 0;
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}
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EXPORT_SYMBOL(fscache_add_cache);
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/**
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* fscache_begin_cache_access - Pin a cache so it can be accessed
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* @cache: The cache-level cookie
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* @why: An indication of the circumstances of the access for tracing
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*
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* Attempt to pin the cache to prevent it from going away whilst we're
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* accessing it and returns true if successful. This works as follows:
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*
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* (1) If the cache tests as not live (state is not FSCACHE_CACHE_IS_ACTIVE),
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* then we return false to indicate access was not permitted.
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*
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* (2) If the cache tests as live, then we increment the n_accesses count and
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* then recheck the liveness, ending the access if it ceased to be live.
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*
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* (3) When we end the access, we decrement n_accesses and wake up the any
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* waiters if it reaches 0.
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*
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* (4) Whilst the cache is caching, n_accesses is kept artificially
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* incremented to prevent wakeups from happening.
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*
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* (5) When the cache is taken offline, the state is changed to prevent new
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* accesses, n_accesses is decremented and we wait for n_accesses to
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* become 0.
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*/
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bool fscache_begin_cache_access(struct fscache_cache *cache, enum fscache_access_trace why)
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{
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int n_accesses;
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if (!fscache_cache_is_live(cache))
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return false;
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n_accesses = atomic_inc_return(&cache->n_accesses);
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smp_mb__after_atomic(); /* Reread live flag after n_accesses */
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trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref),
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n_accesses, why);
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if (!fscache_cache_is_live(cache)) {
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fscache_end_cache_access(cache, fscache_access_unlive);
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return false;
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}
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return true;
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}
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/**
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* fscache_end_cache_access - Unpin a cache at the end of an access.
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* @cache: The cache-level cookie
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* @why: An indication of the circumstances of the access for tracing
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*
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* Unpin a cache after we've accessed it. The @why indicator is merely
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* provided for tracing purposes.
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*/
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void fscache_end_cache_access(struct fscache_cache *cache, enum fscache_access_trace why)
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{
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int n_accesses;
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smp_mb__before_atomic();
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n_accesses = atomic_dec_return(&cache->n_accesses);
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trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref),
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n_accesses, why);
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if (n_accesses == 0)
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wake_up_var(&cache->n_accesses);
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}
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/**
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* fscache_io_error - Note a cache I/O error
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* @cache: The record describing the cache
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*
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* Note that an I/O error occurred in a cache and that it should no longer be
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* used for anything. This also reports the error into the kernel log.
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*
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* See Documentation/filesystems/caching/backend-api.rst for a complete
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* description.
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*/
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void fscache_io_error(struct fscache_cache *cache)
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{
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if (fscache_set_cache_state_maybe(cache,
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FSCACHE_CACHE_IS_ACTIVE,
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FSCACHE_CACHE_GOT_IOERROR))
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pr_err("Cache '%s' stopped due to I/O error\n",
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cache->name);
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}
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EXPORT_SYMBOL(fscache_io_error);
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/**
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* fscache_withdraw_cache - Withdraw a cache from the active service
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* @cache: The cache cookie
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*
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* Begin the process of withdrawing a cache from service. This stops new
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* cache-level and volume-level accesses from taking place and waits for
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* currently ongoing cache-level accesses to end.
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*/
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void fscache_withdraw_cache(struct fscache_cache *cache)
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{
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int n_accesses;
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pr_notice("Withdrawing cache \"%s\" (%u objs)\n",
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cache->name, atomic_read(&cache->object_count));
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fscache_set_cache_state(cache, FSCACHE_CACHE_IS_WITHDRAWN);
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/* Allow wakeups on dec-to-0 */
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n_accesses = atomic_dec_return(&cache->n_accesses);
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trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref),
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n_accesses, fscache_access_cache_unpin);
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wait_var_event(&cache->n_accesses,
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atomic_read(&cache->n_accesses) == 0);
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}
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EXPORT_SYMBOL(fscache_withdraw_cache);
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#ifdef CONFIG_PROC_FS
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static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW";
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/*
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* Generate a list of caches in /proc/fs/fscache/caches
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*/
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static int fscache_caches_seq_show(struct seq_file *m, void *v)
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{
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struct fscache_cache *cache;
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if (v == &fscache_caches) {
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seq_puts(m,
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"CACHE REF VOLS OBJS ACCES S NAME\n"
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"======== ===== ===== ===== ===== = ===============\n"
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);
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return 0;
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}
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cache = list_entry(v, struct fscache_cache, cache_link);
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seq_printf(m,
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"%08x %5d %5d %5d %5d %c %s\n",
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cache->debug_id,
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refcount_read(&cache->ref),
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atomic_read(&cache->n_volumes),
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atomic_read(&cache->object_count),
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atomic_read(&cache->n_accesses),
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fscache_cache_states[cache->state],
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cache->name ?: "-");
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return 0;
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}
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static void *fscache_caches_seq_start(struct seq_file *m, loff_t *_pos)
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__acquires(fscache_addremove_sem)
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{
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down_read(&fscache_addremove_sem);
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return seq_list_start_head(&fscache_caches, *_pos);
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}
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static void *fscache_caches_seq_next(struct seq_file *m, void *v, loff_t *_pos)
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{
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return seq_list_next(v, &fscache_caches, _pos);
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}
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static void fscache_caches_seq_stop(struct seq_file *m, void *v)
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__releases(fscache_addremove_sem)
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{
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up_read(&fscache_addremove_sem);
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}
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const struct seq_operations fscache_caches_seq_ops = {
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.start = fscache_caches_seq_start,
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.next = fscache_caches_seq_next,
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.stop = fscache_caches_seq_stop,
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.show = fscache_caches_seq_show,
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};
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#endif /* CONFIG_PROC_FS */
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