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[PATCH-tip v6 22/22] futex: Dump internal futex state via debugfs

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For debugging purpose, it is sometimes useful to dump the internal
states in the futex hash bucket table. This patch adds a file
"futex_hash_table" in debugfs root filesystem to dump the internal
futex states.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/futex.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index a199574..7691a70 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -4474,3 +4474,85 @@ static int __init futex_init(void)
 	return 0;
 }
 core_initcall(futex_init);
+
+#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SMP)
+/*
+ * Debug code to dump selected content of in-kernel futex hash bucket table.
+ */
+#include <linux/debugfs.h>
+
+static int futex_dump_show(struct seq_file *m, void *arg)
+{
+	struct futex_hash_bucket *hb = arg;
+	struct futex_state *state;
+	int i;
+
+	if (list_empty(&hb->fs_head))
+		return 0;
+
+	seq_printf(m, "\nHash bucket %d:\n", (int)(hb - futex_queues));
+	spin_lock(&hb->fs_lock);
+	i = 0;
+	list_for_each_entry(state, &hb->fs_head, fs_list) {
+		seq_printf(m, "  Futex state %d\n", i++);
+		if (state->owner)
+			seq_printf(m, "    owner PID = %d\n",
+				   task_pid_vnr(state->owner));
+		if (state->mutex_owner)
+			seq_printf(m, "    mutex owner PID = %d\n",
+				   task_pid_vnr(state->mutex_owner));
+		seq_printf(m, "    reference count = %d\n",
+			   atomic_read(&state->refcount));
+		seq_printf(m, "    handoff PID = %d\n", state->handoff_pid);
+	}
+	spin_unlock(&hb->fs_lock);
+	return 0;
+}
+
+static void *futex_dump_start(struct seq_file *m, loff_t *pos)
+{
+	return (*pos < futex_hashsize) ? &futex_queues[*pos] : NULL;
+}
+
+static void *futex_dump_next(struct seq_file *m, void *arg, loff_t *pos)
+{
+	(*pos)++;
+	return (*pos < futex_hashsize) ? &futex_queues[*pos] : NULL;
+}
+
+static void futex_dump_stop(struct seq_file *m, void *arg)
+{
+}
+
+static const struct seq_operations futex_dump_op = {
+	.start = futex_dump_start,
+	.next  = futex_dump_next,
+	.stop  = futex_dump_stop,
+	.show  = futex_dump_show,
+};
+
+static int futex_dump_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &futex_dump_op);
+}
+
+static const struct file_operations fops_futex_dump = {
+	.open	 = futex_dump_open,
+	.read	 = seq_read,
+	.llseek	 = seq_lseek,
+	.release = seq_release,
+};
+
+/*
+ * Initialize debugfs for the futex hash bucket table dump.
+ */
+static int __init init_futex_dump(void)
+{
+	if (!debugfs_create_file("futex_hash_table", 0400, NULL, NULL,
+				 &fops_futex_dump))
+		return -ENOMEM;
+	return 0;
+}
+fs_initcall(init_futex_dump);
+
+#endif /* CONFIG_DEBUG_FS && CONFIG_SMP */
-- 
1.8.3.1

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[PATCH-tip v6 00/22] futex: Introducing throughput-optimized (TP) futexes Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 12/22] TP-futex: Return status code on FUTEX_LOCK calls Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 11/22] TP-futex: Implement lock handoff to prevent lock starvation Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 20/22] perf bench: Extend mutex/rwlock futex suite to test TP futexes Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 21/22] sched, TP-futex: Make wake_up_q() return wakeup count Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 02/22] perf bench: New microbenchmark for userspace rwlock performance Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 03/22] futex: Consolidate duplicated timer setup code Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 04/22] futex: Rename futex_pi_state to futex_state Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 22/22] futex: Dump internal futex state via debugfs Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 19/22] TP-futex, doc: Update TP futexes document on shared locking Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 08/22] futex: Allow direct attachment of futex_state objects to hash bucket Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 09/22] futex: Introduce throughput-optimized (TP) futexes Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 01/22] perf bench: New microbenchmark for userspace mutex performance Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 18/22] TP-futex: Group readers together in wait queue Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
    Re: [PATCH-tip v6 18/22] TP-futex: Group readers together in wait  queue kbuild test robot <lkp@intel.com> - 2017-03-24 09:30 +0100
    Re: [PATCH-tip v6 18/22] TP-futex: Group readers together in wait  queue kbuild test robot <lkp@intel.com> - 2017-03-24 09:40 +0100
  [PATCH-tip v6 16/22] TP-futex: Support userspace reader/writer locks Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 13/22] TP-futex: Add timeout support Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 17/22] TP-futex: Enable kernel reader lock stealing Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 05/22] futex: Add helpers to get & cmpxchg futex value without lock Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 10/22] TP-futex: Enable robust handling Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 07/22] futex: Add a new futex type field into futex_state Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 15/22] TP-futex, doc: Add TP futexes documentation Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100
  [PATCH-tip v6 14/22] TP-futex: Optionally return EAGAIN for userspace locking Waiman Long <longman@redhat.com> - 2017-03-22 18:50 +0100

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