From 3d7a641e544e428191667e8b1f83f96fa46dbd65 Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 19 Nov 2009 18:10:23 +0000 Subject: [PATCH] SLOW_WORK: Wait for outstanding work items belonging to a module to clear Wait for outstanding slow work items belonging to a module to clear when unregistering that module as a user of the facility. This prevents the put_ref code of a work item from being taken away before it returns. Signed-off-by: David Howells --- Documentation/slow-work.txt | 13 +++- fs/fscache/main.c | 6 +- fs/fscache/object.c | 1 + fs/fscache/operation.c | 1 + fs/gfs2/main.c | 4 +- fs/gfs2/recovery.c | 1 + include/linux/slow-work.h | 8 ++- kernel/slow-work.c | 132 ++++++++++++++++++++++++++++++++++-- 8 files changed, 150 insertions(+), 16 deletions(-) diff --git a/Documentation/slow-work.txt b/Documentation/slow-work.txt index ebc50f808ea4..f12fda31dcdc 100644 --- a/Documentation/slow-work.txt +++ b/Documentation/slow-work.txt @@ -64,9 +64,11 @@ USING SLOW WORK ITEMS Firstly, a module or subsystem wanting to make use of slow work items must register its interest: - int ret = slow_work_register_user(); + int ret = slow_work_register_user(struct module *module); -This will return 0 if successful, or a -ve error upon failure. +This will return 0 if successful, or a -ve error upon failure. The module +pointer should be the module interested in using this facility (almost +certainly THIS_MODULE). Slow work items may then be set up by: @@ -110,7 +112,12 @@ operation. When all a module's slow work items have been processed, and the module has no further interest in the facility, it should unregister its interest: - slow_work_unregister_user(); + slow_work_unregister_user(struct module *module); + +The module pointer is used to wait for all outstanding work items for that +module before completing the unregistration. This prevents the put_ref() code +from being taken away before it completes. module should almost certainly be +THIS_MODULE. =============== diff --git a/fs/fscache/main.c b/fs/fscache/main.c index 4de41b597499..add6bdb53f04 100644 --- a/fs/fscache/main.c +++ b/fs/fscache/main.c @@ -48,7 +48,7 @@ static int __init fscache_init(void) { int ret; - ret = slow_work_register_user(); + ret = slow_work_register_user(THIS_MODULE); if (ret < 0) goto error_slow_work; @@ -80,7 +80,7 @@ error_kobj: error_cookie_jar: fscache_proc_cleanup(); error_proc: - slow_work_unregister_user(); + slow_work_unregister_user(THIS_MODULE); error_slow_work: return ret; } @@ -97,7 +97,7 @@ static void __exit fscache_exit(void) kobject_put(fscache_root); kmem_cache_destroy(fscache_cookie_jar); fscache_proc_cleanup(); - slow_work_unregister_user(); + slow_work_unregister_user(THIS_MODULE); printk(KERN_NOTICE "FS-Cache: Unloaded\n"); } diff --git a/fs/fscache/object.c b/fs/fscache/object.c index 392a41b1b79d..d236eb1d6f37 100644 --- a/fs/fscache/object.c +++ b/fs/fscache/object.c @@ -45,6 +45,7 @@ static void fscache_enqueue_dependents(struct fscache_object *); static void fscache_dequeue_object(struct fscache_object *); const struct slow_work_ops fscache_object_slow_work_ops = { + .owner = THIS_MODULE, .get_ref = fscache_object_slow_work_get_ref, .put_ref = fscache_object_slow_work_put_ref, .execute = fscache_object_slow_work_execute, diff --git a/fs/fscache/operation.c b/fs/fscache/operation.c index e7f8d53b8b6b..f1a2857b2ff5 100644 --- a/fs/fscache/operation.c +++ b/fs/fscache/operation.c @@ -453,6 +453,7 @@ static void fscache_op_execute(struct slow_work *work) } const struct slow_work_ops fscache_op_slow_work_ops = { + .owner = THIS_MODULE, .get_ref = fscache_op_get_ref, .put_ref = fscache_op_put_ref, .execute = fscache_op_execute, diff --git a/fs/gfs2/main.c b/fs/gfs2/main.c index eacd78a5d082..5b31f7741a8f 100644 --- a/fs/gfs2/main.c +++ b/fs/gfs2/main.c @@ -114,7 +114,7 @@ static int __init init_gfs2_fs(void) if (error) goto fail_unregister; - error = slow_work_register_user(); + error = slow_work_register_user(THIS_MODULE); if (error) goto fail_slow; @@ -163,7 +163,7 @@ static void __exit exit_gfs2_fs(void) gfs2_unregister_debugfs(); unregister_filesystem(&gfs2_fs_type); unregister_filesystem(&gfs2meta_fs_type); - slow_work_unregister_user(); + slow_work_unregister_user(THIS_MODULE); kmem_cache_destroy(gfs2_quotad_cachep); kmem_cache_destroy(gfs2_rgrpd_cachep); diff --git a/fs/gfs2/recovery.c b/fs/gfs2/recovery.c index 59d2695509d3..b2bb779f09ed 100644 --- a/fs/gfs2/recovery.c +++ b/fs/gfs2/recovery.c @@ -593,6 +593,7 @@ fail: } struct slow_work_ops gfs2_recover_ops = { + .owner = THIS_MODULE, .get_ref = gfs2_recover_get_ref, .put_ref = gfs2_recover_put_ref, .execute = gfs2_recover_work, diff --git a/include/linux/slow-work.h b/include/linux/slow-work.h index b65c8881f07a..9adb2b30754f 100644 --- a/include/linux/slow-work.h +++ b/include/linux/slow-work.h @@ -24,6 +24,9 @@ struct slow_work; * The operations used to support slow work items */ struct slow_work_ops { + /* owner */ + struct module *owner; + /* get a ref on a work item * - return 0 if successful, -ve if not */ @@ -42,6 +45,7 @@ struct slow_work_ops { * queued */ struct slow_work { + struct module *owner; /* the owning module */ unsigned long flags; #define SLOW_WORK_PENDING 0 /* item pending (further) execution */ #define SLOW_WORK_EXECUTING 1 /* item currently executing */ @@ -84,8 +88,8 @@ static inline void vslow_work_init(struct slow_work *work, } extern int slow_work_enqueue(struct slow_work *work); -extern int slow_work_register_user(void); -extern void slow_work_unregister_user(void); +extern int slow_work_register_user(struct module *owner); +extern void slow_work_unregister_user(struct module *owner); #ifdef CONFIG_SYSCTL extern ctl_table slow_work_sysctls[]; diff --git a/kernel/slow-work.c b/kernel/slow-work.c index 0d31135efbf4..dd08f376e406 100644 --- a/kernel/slow-work.c +++ b/kernel/slow-work.c @@ -22,6 +22,8 @@ #define SLOW_WORK_OOM_TIMEOUT (5 * HZ) /* can't start new threads for 5s after * OOM */ +#define SLOW_WORK_THREAD_LIMIT 255 /* abs maximum number of slow-work threads */ + static void slow_work_cull_timeout(unsigned long); static void slow_work_oom_timeout(unsigned long); @@ -46,7 +48,7 @@ static unsigned vslow_work_proportion = 50; /* % of threads that may process #ifdef CONFIG_SYSCTL static const int slow_work_min_min_threads = 2; -static int slow_work_max_max_threads = 255; +static int slow_work_max_max_threads = SLOW_WORK_THREAD_LIMIT; static const int slow_work_min_vslow = 1; static const int slow_work_max_vslow = 99; @@ -97,6 +99,23 @@ static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0); static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0); static struct slow_work slow_work_new_thread; /* new thread starter */ +/* + * slow work ID allocation (use slow_work_queue_lock) + */ +static DECLARE_BITMAP(slow_work_ids, SLOW_WORK_THREAD_LIMIT); + +/* + * Unregistration tracking to prevent put_ref() from disappearing during module + * unload + */ +#ifdef CONFIG_MODULES +static struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT]; +static struct module *slow_work_unreg_module; +static struct slow_work *slow_work_unreg_work_item; +static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq); +static DEFINE_MUTEX(slow_work_unreg_sync_lock); +#endif + /* * The queues of work items and the lock governing access to them. These are * shared between all the CPUs. It doesn't make sense to have per-CPU queues @@ -149,8 +168,11 @@ static unsigned slow_work_calc_vsmax(void) * Attempt to execute stuff queued on a slow thread. Return true if we managed * it, false if there was nothing to do. */ -static bool slow_work_execute(void) +static bool slow_work_execute(int id) { +#ifdef CONFIG_MODULES + struct module *module; +#endif struct slow_work *work = NULL; unsigned vsmax; bool very_slow; @@ -186,6 +208,12 @@ static bool slow_work_execute(void) } else { very_slow = false; /* avoid the compiler warning */ } + +#ifdef CONFIG_MODULES + if (work) + slow_work_thread_processing[id] = work->owner; +#endif + spin_unlock_irq(&slow_work_queue_lock); if (!work) @@ -219,7 +247,18 @@ static bool slow_work_execute(void) spin_unlock_irq(&slow_work_queue_lock); } + /* sort out the race between module unloading and put_ref() */ work->ops->put_ref(work); + +#ifdef CONFIG_MODULES + module = slow_work_thread_processing[id]; + slow_work_thread_processing[id] = NULL; + smp_mb(); + if (slow_work_unreg_work_item == work || + slow_work_unreg_module == module) + wake_up_all(&slow_work_unreg_wq); +#endif + return true; auto_requeue: @@ -232,6 +271,7 @@ auto_requeue: else list_add_tail(&work->link, &slow_work_queue); spin_unlock_irq(&slow_work_queue_lock); + slow_work_thread_processing[id] = NULL; return true; } @@ -368,13 +408,22 @@ static inline bool slow_work_available(int vsmax) */ static int slow_work_thread(void *_data) { - int vsmax; + int vsmax, id; DEFINE_WAIT(wait); set_freezable(); set_user_nice(current, -5); + /* allocate ourselves an ID */ + spin_lock_irq(&slow_work_queue_lock); + id = find_first_zero_bit(slow_work_ids, SLOW_WORK_THREAD_LIMIT); + BUG_ON(id < 0 || id >= SLOW_WORK_THREAD_LIMIT); + __set_bit(id, slow_work_ids); + spin_unlock_irq(&slow_work_queue_lock); + + sprintf(current->comm, "kslowd%03u", id); + for (;;) { vsmax = vslow_work_proportion; vsmax *= atomic_read(&slow_work_thread_count); @@ -395,7 +444,7 @@ static int slow_work_thread(void *_data) vsmax *= atomic_read(&slow_work_thread_count); vsmax /= 100; - if (slow_work_available(vsmax) && slow_work_execute()) { + if (slow_work_available(vsmax) && slow_work_execute(id)) { cond_resched(); if (list_empty(&slow_work_queue) && list_empty(&vslow_work_queue) && @@ -412,6 +461,10 @@ static int slow_work_thread(void *_data) break; } + spin_lock_irq(&slow_work_queue_lock); + __clear_bit(id, slow_work_ids); + spin_unlock_irq(&slow_work_queue_lock); + if (atomic_dec_and_test(&slow_work_thread_count)) complete_and_exit(&slow_work_last_thread_exited, 0); return 0; @@ -475,6 +528,7 @@ static void slow_work_new_thread_execute(struct slow_work *work) } static const struct slow_work_ops slow_work_new_thread_ops = { + .owner = THIS_MODULE, .get_ref = slow_work_new_thread_get_ref, .put_ref = slow_work_new_thread_put_ref, .execute = slow_work_new_thread_execute, @@ -546,12 +600,13 @@ static int slow_work_max_threads_sysctl(struct ctl_table *table, int write, /** * slow_work_register_user - Register a user of the facility + * @module: The module about to make use of the facility * * Register a user of the facility, starting up the initial threads if there * aren't any other users at this point. This will return 0 if successful, or * an error if not. */ -int slow_work_register_user(void) +int slow_work_register_user(struct module *module) { struct task_struct *p; int loop; @@ -598,14 +653,79 @@ error: } EXPORT_SYMBOL(slow_work_register_user); +/* + * wait for all outstanding items from the calling module to complete + * - note that more items may be queued whilst we're waiting + */ +static void slow_work_wait_for_items(struct module *module) +{ + DECLARE_WAITQUEUE(myself, current); + struct slow_work *work; + int loop; + + mutex_lock(&slow_work_unreg_sync_lock); + add_wait_queue(&slow_work_unreg_wq, &myself); + + for (;;) { + spin_lock_irq(&slow_work_queue_lock); + + /* first of all, we wait for the last queued item in each list + * to be processed */ + list_for_each_entry_reverse(work, &vslow_work_queue, link) { + if (work->owner == module) { + set_current_state(TASK_UNINTERRUPTIBLE); + slow_work_unreg_work_item = work; + goto do_wait; + } + } + list_for_each_entry_reverse(work, &slow_work_queue, link) { + if (work->owner == module) { + set_current_state(TASK_UNINTERRUPTIBLE); + slow_work_unreg_work_item = work; + goto do_wait; + } + } + + /* then we wait for the items being processed to finish */ + slow_work_unreg_module = module; + smp_mb(); + for (loop = 0; loop < SLOW_WORK_THREAD_LIMIT; loop++) { + if (slow_work_thread_processing[loop] == module) + goto do_wait; + } + spin_unlock_irq(&slow_work_queue_lock); + break; /* okay, we're done */ + + do_wait: + spin_unlock_irq(&slow_work_queue_lock); + schedule(); + slow_work_unreg_work_item = NULL; + slow_work_unreg_module = NULL; + } + + remove_wait_queue(&slow_work_unreg_wq, &myself); + mutex_unlock(&slow_work_unreg_sync_lock); +} + /** * slow_work_unregister_user - Unregister a user of the facility + * @module: The module whose items should be cleared * * Unregister a user of the facility, killing all the threads if this was the * last one. + * + * This waits for all the work items belonging to the nominated module to go + * away before proceeding. */ -void slow_work_unregister_user(void) +void slow_work_unregister_user(struct module *module) { + /* first of all, wait for all outstanding items from the calling module + * to complete */ + if (module) + slow_work_wait_for_items(module); + + /* then we can actually go about shutting down the facility if need + * be */ mutex_lock(&slow_work_user_lock); BUG_ON(slow_work_user_count <= 0);