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authorTejun Heo <tj@kernel.org>2014-07-01 16:41:03 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-07-02 09:32:09 -0700
commitecca47ce8294843045e7465d76fee84dbf07a004 (patch)
treefdd191b4517786683da541715670c08e77a3fb6a /fs/kernfs
parent4c834452aad01531db949414f94f817a86348d59 (diff)
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: [<ffffffffa0039042>] virtblk_done+0x42/0xe0 [virtio_blk] #1: (&(&bitmap->counts.lock)->rlock){-.....}, at: [<ffffffff81633718>] bitmap_endwrite+0x68/0x240 irq event stamp: 33518 hardirqs last enabled at (33515): [<ffffffff8102544f>] default_idle+0x1f/0x230 hardirqs last disabled at (33516): [<ffffffff818122ed>] common_interrupt+0x6d/0x72 softirqs last enabled at (33518): [<ffffffff810a1272>] _local_bh_enable+0x22/0x50 softirqs last disabled at (33517): [<ffffffff810a29e0>] 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: <IRQ> [<ffffffff81807b4c>] dump_stack+0x4d/0x66 [<ffffffff810d4f14>] __might_sleep+0x184/0x240 [<ffffffff8180caf2>] mutex_lock_nested+0x42/0x440 [<ffffffff812d76a0>] kernfs_notify+0x90/0x150 [<ffffffff8163377c>] bitmap_endwrite+0xcc/0x240 [<ffffffffa00de863>] close_write+0x93/0xb0 [raid1] [<ffffffffa00df029>] r1_bio_write_done+0x29/0x50 [raid1] [<ffffffffa00e0474>] raid1_end_write_request+0xe4/0x260 [raid1] [<ffffffff813acb8b>] bio_endio+0x6b/0xa0 [<ffffffff813b46c4>] blk_update_request+0x94/0x420 [<ffffffff813bf0ea>] blk_mq_end_io+0x1a/0x70 [<ffffffffa00392c2>] virtblk_request_done+0x32/0x80 [virtio_blk] [<ffffffff813c0648>] __blk_mq_complete_request+0x88/0x120 [<ffffffff813c070a>] blk_mq_complete_request+0x2a/0x30 [<ffffffffa0039066>] virtblk_done+0x66/0xe0 [virtio_blk] [<ffffffffa002535a>] vring_interrupt+0x3a/0xa0 [virtio_ring] [<ffffffff81116177>] handle_irq_event_percpu+0x77/0x340 [<ffffffff8111647d>] handle_irq_event+0x3d/0x60 [<ffffffff81119436>] handle_edge_irq+0x66/0x130 [<ffffffff8101c3e4>] handle_irq+0x84/0x150 [<ffffffff818146ad>] do_IRQ+0x4d/0xe0 [<ffffffff818122f2>] common_interrupt+0x72/0x72 <EOI> [<ffffffff8105f706>] ? native_safe_halt+0x6/0x10 [<ffffffff81025454>] default_idle+0x24/0x230 [<ffffffff81025f9f>] arch_cpu_idle+0xf/0x20 [<ffffffff810f5adc>] cpu_startup_entry+0x37c/0x7b0 [<ffffffff8104df1b>] 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 <tj@kernel.org> Reported-by: Josh Boyer <jwboyer@fedoraproject.org> Cc: Jens Axboe <axboe@kernel.dk> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/kernfs')
-rw-r--r--fs/kernfs/file.c69
1 files changed, 55 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);