From ecca47ce8294843045e7465d76fee84dbf07a004 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 1 Jul 2014 16:41:03 -0400 Subject: [PATCH] kernfs: kernfs_notify() must be useable from non-sleepable contexts d911d9874801 ("kernfs: make kernfs_notify() trigger inotify events too") added fsnotify triggering to kernfs_notify() which requires a sleepable context. There are already existing users of kernfs_notify() which invoke it from an atomic context and in general it's silly to require a sleepable context for triggering a notification. The following is an invalid context bug triggerd by md invoking sysfs_notify() from IO completion path. BUG: sleeping function called from invalid context at kernel/locking/mutex.c:586 in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/1 2 locks held by swapper/1/0: #0: (&(&vblk->vq_lock)->rlock){-.-...}, at: [] virtblk_done+0x42/0xe0 [virtio_blk] #1: (&(&bitmap->counts.lock)->rlock){-.....}, at: [] bitmap_endwrite+0x68/0x240 irq event stamp: 33518 hardirqs last enabled at (33515): [] default_idle+0x1f/0x230 hardirqs last disabled at (33516): [] common_interrupt+0x6d/0x72 softirqs last enabled at (33518): [] _local_bh_enable+0x22/0x50 softirqs last disabled at (33517): [] irq_enter+0x60/0x80 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.16.0-0.rc2.git2.1.fc21.x86_64 #1 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 0000000000000000 f90db13964f4ee05 ffff88007d403b80 ffffffff81807b4c 0000000000000000 ffff88007d403ba8 ffffffff810d4f14 0000000000000000 0000000000441800 ffff880078fa1780 ffff88007d403c38 ffffffff8180caf2 Call Trace: [] dump_stack+0x4d/0x66 [] __might_sleep+0x184/0x240 [] mutex_lock_nested+0x42/0x440 [] kernfs_notify+0x90/0x150 [] bitmap_endwrite+0xcc/0x240 [] close_write+0x93/0xb0 [raid1] [] r1_bio_write_done+0x29/0x50 [raid1] [] raid1_end_write_request+0xe4/0x260 [raid1] [] bio_endio+0x6b/0xa0 [] blk_update_request+0x94/0x420 [] blk_mq_end_io+0x1a/0x70 [] virtblk_request_done+0x32/0x80 [virtio_blk] [] __blk_mq_complete_request+0x88/0x120 [] blk_mq_complete_request+0x2a/0x30 [] virtblk_done+0x66/0xe0 [virtio_blk] [] vring_interrupt+0x3a/0xa0 [virtio_ring] [] handle_irq_event_percpu+0x77/0x340 [] handle_irq_event+0x3d/0x60 [] handle_edge_irq+0x66/0x130 [] handle_irq+0x84/0x150 [] do_IRQ+0x4d/0xe0 [] common_interrupt+0x72/0x72 [] ? native_safe_halt+0x6/0x10 [] default_idle+0x24/0x230 [] arch_cpu_idle+0xf/0x20 [] cpu_startup_entry+0x37c/0x7b0 [] start_secondary+0x25b/0x300 This patch fixes it by punting the notification delivery through a work item. This ends up adding an extra pointer to kernfs_elem_attr enlarging kernfs_node by a pointer, which is not ideal but not a very big deal either. If this turns out to be an actual issue, we can move kernfs_elem_attr->size to kernfs_node->iattr later. Signed-off-by: Tejun Heo Reported-by: Josh Boyer Cc: Jens Axboe Reviewed-by: Michael S. Tsirkin Signed-off-by: Greg Kroah-Hartman --- fs/kernfs/file.c | 69 +++++++++++++++++++++++++++++++++--------- include/linux/kernfs.h | 1 + 2 files changed, 56 insertions(+), 14 deletions(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index e3d37f607f97..d895b4b7b661 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -39,6 +39,19 @@ struct kernfs_open_node { struct list_head files; /* goes through kernfs_open_file.list */ }; +/* + * kernfs_notify() may be called from any context and bounces notifications + * through a work item. To minimize space overhead in kernfs_node, the + * pending queue is implemented as a singly linked list of kernfs_nodes. + * The list is terminated with the self pointer so that whether a + * kernfs_node is on the list or not can be determined by testing the next + * pointer for NULL. + */ +#define KERNFS_NOTIFY_EOL ((void *)&kernfs_notify_list) + +static DEFINE_SPINLOCK(kernfs_notify_lock); +static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL; + static struct kernfs_open_file *kernfs_of(struct file *file) { return ((struct seq_file *)file->private_data)->private; @@ -783,24 +796,25 @@ static unsigned int kernfs_fop_poll(struct file *filp, poll_table *wait) return DEFAULT_POLLMASK|POLLERR|POLLPRI; } -/** - * kernfs_notify - notify a kernfs file - * @kn: file to notify - * - * Notify @kn such that poll(2) on @kn wakes up. - */ -void kernfs_notify(struct kernfs_node *kn) +static void kernfs_notify_workfn(struct work_struct *work) { - struct kernfs_root *root = kernfs_root(kn); + struct kernfs_node *kn; struct kernfs_open_node *on; struct kernfs_super_info *info; - unsigned long flags; - - if (WARN_ON(kernfs_type(kn) != KERNFS_FILE)) +repeat: + /* pop one off the notify_list */ + spin_lock_irq(&kernfs_notify_lock); + kn = kernfs_notify_list; + if (kn == KERNFS_NOTIFY_EOL) { + spin_unlock_irq(&kernfs_notify_lock); return; + } + kernfs_notify_list = kn->attr.notify_next; + kn->attr.notify_next = NULL; + spin_unlock_irq(&kernfs_notify_lock); /* kick poll */ - spin_lock_irqsave(&kernfs_open_node_lock, flags); + spin_lock_irq(&kernfs_open_node_lock); on = kn->attr.open; if (on) { @@ -808,12 +822,12 @@ void kernfs_notify(struct kernfs_node *kn) wake_up_interruptible(&on->poll); } - spin_unlock_irqrestore(&kernfs_open_node_lock, flags); + spin_unlock_irq(&kernfs_open_node_lock); /* kick fsnotify */ mutex_lock(&kernfs_mutex); - list_for_each_entry(info, &root->supers, node) { + list_for_each_entry(info, &kernfs_root(kn)->supers, node) { struct inode *inode; struct dentry *dentry; @@ -833,6 +847,33 @@ void kernfs_notify(struct kernfs_node *kn) } mutex_unlock(&kernfs_mutex); + kernfs_put(kn); + goto repeat; +} + +/** + * kernfs_notify - notify a kernfs file + * @kn: file to notify + * + * Notify @kn such that poll(2) on @kn wakes up. Maybe be called from any + * context. + */ +void kernfs_notify(struct kernfs_node *kn) +{ + static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn); + unsigned long flags; + + if (WARN_ON(kernfs_type(kn) != KERNFS_FILE)) + return; + + spin_lock_irqsave(&kernfs_notify_lock, flags); + if (!kn->attr.notify_next) { + kernfs_get(kn); + kn->attr.notify_next = kernfs_notify_list; + kernfs_notify_list = kn; + schedule_work(&kernfs_notify_work); + } + spin_unlock_irqrestore(&kernfs_notify_lock, flags); } EXPORT_SYMBOL_GPL(kernfs_notify); diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h index 17aa1cce6f8e..145375ea0bd9 100644 --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -91,6 +91,7 @@ struct kernfs_elem_attr { const struct kernfs_ops *ops; struct kernfs_open_node *open; loff_t size; + struct kernfs_node *notify_next; /* for kernfs_notify() */ }; /* -- 2.20.1