From d110271e1f4140a9fb06d968b1afe9ca56a6064e Mon Sep 17 00:00:00 2001 From: Alex Chiang Date: Wed, 25 Mar 2009 15:11:36 -0600 Subject: [PATCH] sysfs: don't use global workqueue in sysfs_schedule_callback() A sysfs attribute using sysfs_schedule_callback() to commit suicide may end up calling device_unregister(), which will eventually call a driver's ->remove function. Drivers may call flush_scheduled_work() in their shutdown routines, in which case lockdep will complain with something like the following: ============================================= [ INFO: possible recursive locking detected ] 2.6.29-rc8-kk #1 --------------------------------------------- events/4/56 is trying to acquire lock: (events){--..}, at: [] flush_workqueue+0x0/0xa0 but task is already holding lock: (events){--..}, at: [] run_workqueue+0x108/0x230 other info that might help us debug this: 3 locks held by events/4/56: #0: (events){--..}, at: [] run_workqueue+0x108/0x230 #1: (&ss->work){--..}, at: [] run_workqueue+0x108/0x230 #2: (pci_remove_rescan_mutex){--..}, at: [] remove_callback+0x21/0x40 stack backtrace: Pid: 56, comm: events/4 Not tainted 2.6.29-rc8-kk #1 Call Trace: [] validate_chain+0xb7d/0x1260 [] __lock_acquire+0x42e/0xa40 [] lock_acquire+0x58/0x80 [] ? flush_workqueue+0x0/0xa0 [] flush_workqueue+0x4d/0xa0 [] ? flush_workqueue+0x0/0xa0 [] flush_scheduled_work+0x10/0x20 [] e1000_remove+0x55/0xfe [e1000e] [] ? sysfs_schedule_callback_work+0x0/0x50 [] pci_device_remove+0x32/0x70 [] __device_release_driver+0x59/0x90 [] device_release_driver+0x2b/0x40 [] bus_remove_device+0xa6/0x120 [] device_del+0x12b/0x190 [] device_unregister+0x26/0x70 [] pci_stop_dev+0x49/0x60 [] pci_remove_bus_device+0x40/0xc0 [] remove_callback+0x29/0x40 [] sysfs_schedule_callback_work+0x1f/0x50 [] run_workqueue+0x15a/0x230 [] ? run_workqueue+0x108/0x230 [] worker_thread+0x9f/0x100 [] ? autoremove_wake_function+0x0/0x40 [] ? worker_thread+0x0/0x100 [] kthread+0x4d/0x80 [] child_rip+0xa/0x20 [] ? restore_args+0x0/0x30 [] ? kthread+0x0/0x80 [] ? child_rip+0x0/0x20 Although we know that the device_unregister path will never acquire a lock that a driver might try to acquire in its ->remove, in general we should never attempt to flush a workqueue from within the same workqueue, and lockdep rightly complains. So as long as sysfs attributes cannot commit suicide directly and we are stuck with this callback mechanism, put the sysfs callbacks on their own workqueue instead of the global one. This has the side benefit that if a suicidal sysfs attribute kicks off a long chain of ->remove callbacks, we no longer induce a long delay on the global queue. This also fixes a missing module_put in the error path introduced by sysfs-only-allow-one-scheduled-removal-callback-per-kobj.patch. We never destroy the workqueue, but I'm not sure that's a problem. Reported-by: Kenji Kaneshige Tested-by: Kenji Kaneshige Signed-off-by: Alex Chiang Signed-off-by: Greg Kroah-Hartman --- fs/sysfs/file.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c index 289c43a47263..979e9379fb5a 100644 --- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -667,6 +667,7 @@ struct sysfs_schedule_callback_struct { struct work_struct work; }; +static struct workqueue_struct *sysfs_workqueue; static DEFINE_MUTEX(sysfs_workq_mutex); static LIST_HEAD(sysfs_workq); static void sysfs_schedule_callback_work(struct work_struct *work) @@ -715,11 +716,20 @@ int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *), mutex_lock(&sysfs_workq_mutex); list_for_each_entry_safe(ss, tmp, &sysfs_workq, workq_list) if (ss->kobj == kobj) { + module_put(owner); mutex_unlock(&sysfs_workq_mutex); return -EAGAIN; } mutex_unlock(&sysfs_workq_mutex); + if (sysfs_workqueue == NULL) { + sysfs_workqueue = create_workqueue("sysfsd"); + if (sysfs_workqueue == NULL) { + module_put(owner); + return -ENOMEM; + } + } + ss = kmalloc(sizeof(*ss), GFP_KERNEL); if (!ss) { module_put(owner); @@ -735,7 +745,7 @@ int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *), mutex_lock(&sysfs_workq_mutex); list_add_tail(&ss->workq_list, &sysfs_workq); mutex_unlock(&sysfs_workq_mutex); - schedule_work(&ss->work); + queue_work(sysfs_workqueue, &ss->work); return 0; } EXPORT_SYMBOL_GPL(sysfs_schedule_callback); -- GitLab