x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 825 insertions, 0 deletions

diff --git a/fs/dlm/debug_fs.c b/fs/dlm/debug_fs.c
new file mode 100644
index 000000000..700a0cbb2
--- /dev/null
+++ b/fs/dlm/debug_fs.c
@@ -0,0 +1,825 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/******************************************************************************
+*******************************************************************************
+**
+**  Copyright (C) 2005-2009 Red Hat, Inc.  All rights reserved.
+**
+**
+*******************************************************************************
+******************************************************************************/
+
+#include <linux/pagemap.h>
+#include <linux/seq_file.h>
+#include <linux/init.h>
+#include <linux/ctype.h>
+#include <linux/debugfs.h>
+#include <linux/slab.h>
+
+#include "dlm_internal.h"
+#include "midcomms.h"
+#include "lock.h"
+#include "ast.h"
+
+#define DLM_DEBUG_BUF_LEN 4096
+static char debug_buf[DLM_DEBUG_BUF_LEN];
+static struct mutex debug_buf_lock;
+
+static struct dentry *dlm_root;
+static struct dentry *dlm_comms;
+
+static char *print_lockmode(int mode)
+{
+	switch (mode) {
+	case DLM_LOCK_IV:
+		return "--";
+	case DLM_LOCK_NL:
+		return "NL";
+	case DLM_LOCK_CR:
+		return "CR";
+	case DLM_LOCK_CW:
+		return "CW";
+	case DLM_LOCK_PR:
+		return "PR";
+	case DLM_LOCK_PW:
+		return "PW";
+	case DLM_LOCK_EX:
+		return "EX";
+	default:
+		return "??";
+	}
+}
+
+static void print_format1_lock(struct seq_file *s, struct dlm_lkb *lkb,
+			       struct dlm_rsb *res)
+{
+	seq_printf(s, "%08x %s", lkb->lkb_id, print_lockmode(lkb->lkb_grmode));
+
+	if (lkb->lkb_status == DLM_LKSTS_CONVERT ||
+	    lkb->lkb_status == DLM_LKSTS_WAITING)
+		seq_printf(s, " (%s)", print_lockmode(lkb->lkb_rqmode));
+
+	if (lkb->lkb_nodeid) {
+		if (lkb->lkb_nodeid != res->res_nodeid)
+			seq_printf(s, " Remote: %3d %08x", lkb->lkb_nodeid,
+				   lkb->lkb_remid);
+		else
+			seq_printf(s, " Master:     %08x", lkb->lkb_remid);
+	}
+
+	if (lkb->lkb_wait_type)
+		seq_printf(s, " wait_type: %d", lkb->lkb_wait_type);
+
+	seq_putc(s, '\n');
+}
+
+static void print_format1(struct dlm_rsb *res, struct seq_file *s)
+{
+	struct dlm_lkb *lkb;
+	int i, lvblen = res->res_ls->ls_lvblen, recover_list, root_list;
+
+	lock_rsb(res);
+
+	seq_printf(s, "\nResource %p Name (len=%d) \"", res, res->res_length);
+
+	for (i = 0; i < res->res_length; i++) {
+		if (isprint(res->res_name[i]))
+			seq_printf(s, "%c", res->res_name[i]);
+		else
+			seq_printf(s, "%c", '.');
+	}
+
+	if (res->res_nodeid > 0)
+		seq_printf(s, "\"\nLocal Copy, Master is node %d\n",
+			   res->res_nodeid);
+	else if (res->res_nodeid == 0)
+		seq_puts(s, "\"\nMaster Copy\n");
+	else if (res->res_nodeid == -1)
+		seq_printf(s, "\"\nLooking up master (lkid %x)\n",
+			   res->res_first_lkid);
+	else
+		seq_printf(s, "\"\nInvalid master %d\n", res->res_nodeid);
+	if (seq_has_overflowed(s))
+		goto out;
+
+	/* Print the LVB: */
+	if (res->res_lvbptr) {
+		seq_puts(s, "LVB: ");
+		for (i = 0; i < lvblen; i++) {
+			if (i == lvblen / 2)
+				seq_puts(s, "\n     ");
+			seq_printf(s, "%02x ",
+				   (unsigned char) res->res_lvbptr[i]);
+		}
+		if (rsb_flag(res, RSB_VALNOTVALID))
+			seq_puts(s, " (INVALID)");
+		seq_putc(s, '\n');
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	root_list = !list_empty(&res->res_root_list);
+	recover_list = !list_empty(&res->res_recover_list);
+
+	if (root_list || recover_list) {
+		seq_printf(s, "Recovery: root %d recover %d flags %lx count %d\n",
+			   root_list, recover_list,
+			   res->res_flags, res->res_recover_locks_count);
+	}
+
+	/* Print the locks attached to this resource */
+	seq_puts(s, "Granted Queue\n");
+	list_for_each_entry(lkb, &res->res_grantqueue, lkb_statequeue) {
+		print_format1_lock(s, lkb, res);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	seq_puts(s, "Conversion Queue\n");
+	list_for_each_entry(lkb, &res->res_convertqueue, lkb_statequeue) {
+		print_format1_lock(s, lkb, res);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	seq_puts(s, "Waiting Queue\n");
+	list_for_each_entry(lkb, &res->res_waitqueue, lkb_statequeue) {
+		print_format1_lock(s, lkb, res);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	if (list_empty(&res->res_lookup))
+		goto out;
+
+	seq_puts(s, "Lookup Queue\n");
+	list_for_each_entry(lkb, &res->res_lookup, lkb_rsb_lookup) {
+		seq_printf(s, "%08x %s",
+			   lkb->lkb_id, print_lockmode(lkb->lkb_rqmode));
+		if (lkb->lkb_wait_type)
+			seq_printf(s, " wait_type: %d", lkb->lkb_wait_type);
+		seq_putc(s, '\n');
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+ out:
+	unlock_rsb(res);
+}
+
+static void print_format2_lock(struct seq_file *s, struct dlm_lkb *lkb,
+			       struct dlm_rsb *r)
+{
+	u64 xid = 0;
+	u64 us;
+
+	if (test_bit(DLM_DFL_USER_BIT, &lkb->lkb_dflags)) {
+		if (lkb->lkb_ua)
+			xid = lkb->lkb_ua->xid;
+	}
+
+	/* microseconds since lkb was added to current queue */
+	us = ktime_to_us(ktime_sub(ktime_get(), lkb->lkb_timestamp));
+
+	/* id nodeid remid pid xid exflags flags sts grmode rqmode time_us
+	   r_nodeid r_len r_name */
+
+	seq_printf(s, "%x %d %x %u %llu %x %x %d %d %d %llu %u %d \"%s\"\n",
+		   lkb->lkb_id,
+		   lkb->lkb_nodeid,
+		   lkb->lkb_remid,
+		   lkb->lkb_ownpid,
+		   (unsigned long long)xid,
+		   lkb->lkb_exflags,
+		   dlm_iflags_val(lkb),
+		   lkb->lkb_status,
+		   lkb->lkb_grmode,
+		   lkb->lkb_rqmode,
+		   (unsigned long long)us,
+		   r->res_nodeid,
+		   r->res_length,
+		   r->res_name);
+}
+
+static void print_format2(struct dlm_rsb *r, struct seq_file *s)
+{
+	struct dlm_lkb *lkb;
+
+	lock_rsb(r);
+
+	list_for_each_entry(lkb, &r->res_grantqueue, lkb_statequeue) {
+		print_format2_lock(s, lkb, r);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	list_for_each_entry(lkb, &r->res_convertqueue, lkb_statequeue) {
+		print_format2_lock(s, lkb, r);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	list_for_each_entry(lkb, &r->res_waitqueue, lkb_statequeue) {
+		print_format2_lock(s, lkb, r);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+ out:
+	unlock_rsb(r);
+}
+
+static void print_format3_lock(struct seq_file *s, struct dlm_lkb *lkb,
+			      int rsb_lookup)
+{
+	u64 xid = 0;
+
+	if (test_bit(DLM_DFL_USER_BIT, &lkb->lkb_dflags)) {
+		if (lkb->lkb_ua)
+			xid = lkb->lkb_ua->xid;
+	}
+
+	seq_printf(s, "lkb %x %d %x %u %llu %x %x %d %d %d %d %d %d %u %llu %llu\n",
+		   lkb->lkb_id,
+		   lkb->lkb_nodeid,
+		   lkb->lkb_remid,
+		   lkb->lkb_ownpid,
+		   (unsigned long long)xid,
+		   lkb->lkb_exflags,
+		   dlm_iflags_val(lkb),
+		   lkb->lkb_status,
+		   lkb->lkb_grmode,
+		   lkb->lkb_rqmode,
+		   lkb->lkb_last_bast_cb_mode,
+		   rsb_lookup,
+		   lkb->lkb_wait_type,
+		   lkb->lkb_lvbseq,
+		   (unsigned long long)ktime_to_ns(lkb->lkb_timestamp),
+		   (unsigned long long)ktime_to_ns(lkb->lkb_last_bast_time));
+}
+
+static void print_format3(struct dlm_rsb *r, struct seq_file *s)
+{
+	struct dlm_lkb *lkb;
+	int i, lvblen = r->res_ls->ls_lvblen;
+	int print_name = 1;
+
+	lock_rsb(r);
+
+	seq_printf(s, "rsb %p %d %x %lx %d %d %u %d ",
+		   r,
+		   r->res_nodeid,
+		   r->res_first_lkid,
+		   r->res_flags,
+		   !list_empty(&r->res_root_list),
+		   !list_empty(&r->res_recover_list),
+		   r->res_recover_locks_count,
+		   r->res_length);
+	if (seq_has_overflowed(s))
+		goto out;
+
+	for (i = 0; i < r->res_length; i++) {
+		if (!isascii(r->res_name[i]) || !isprint(r->res_name[i]))
+			print_name = 0;
+	}
+
+	seq_puts(s, print_name ? "str " : "hex");
+
+	for (i = 0; i < r->res_length; i++) {
+		if (print_name)
+			seq_printf(s, "%c", r->res_name[i]);
+		else
+			seq_printf(s, " %02x", (unsigned char)r->res_name[i]);
+	}
+	seq_putc(s, '\n');
+	if (seq_has_overflowed(s))
+		goto out;
+
+	if (!r->res_lvbptr)
+		goto do_locks;
+
+	seq_printf(s, "lvb %u %d", r->res_lvbseq, lvblen);
+
+	for (i = 0; i < lvblen; i++)
+		seq_printf(s, " %02x", (unsigned char)r->res_lvbptr[i]);
+	seq_putc(s, '\n');
+	if (seq_has_overflowed(s))
+		goto out;
+
+ do_locks:
+	list_for_each_entry(lkb, &r->res_grantqueue, lkb_statequeue) {
+		print_format3_lock(s, lkb, 0);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	list_for_each_entry(lkb, &r->res_convertqueue, lkb_statequeue) {
+		print_format3_lock(s, lkb, 0);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	list_for_each_entry(lkb, &r->res_waitqueue, lkb_statequeue) {
+		print_format3_lock(s, lkb, 0);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+
+	list_for_each_entry(lkb, &r->res_lookup, lkb_rsb_lookup) {
+		print_format3_lock(s, lkb, 1);
+		if (seq_has_overflowed(s))
+			goto out;
+	}
+ out:
+	unlock_rsb(r);
+}
+
+static void print_format4(struct dlm_rsb *r, struct seq_file *s)
+{
+	int our_nodeid = dlm_our_nodeid();
+	int print_name = 1;
+	int i;
+
+	lock_rsb(r);
+
+	seq_printf(s, "rsb %p %d %d %d %d %lu %lx %d ",
+		   r,
+		   r->res_nodeid,
+		   r->res_master_nodeid,
+		   r->res_dir_nodeid,
+		   our_nodeid,
+		   r->res_toss_time,
+		   r->res_flags,
+		   r->res_length);
+
+	for (i = 0; i < r->res_length; i++) {
+		if (!isascii(r->res_name[i]) || !isprint(r->res_name[i]))
+			print_name = 0;
+	}
+
+	seq_puts(s, print_name ? "str " : "hex");
+
+	for (i = 0; i < r->res_length; i++) {
+		if (print_name)
+			seq_printf(s, "%c", r->res_name[i]);
+		else
+			seq_printf(s, " %02x", (unsigned char)r->res_name[i]);
+	}
+	seq_putc(s, '\n');
+	unlock_rsb(r);
+}
+
+static const struct seq_operations format1_seq_ops;
+static const struct seq_operations format2_seq_ops;
+static const struct seq_operations format3_seq_ops;
+static const struct seq_operations format4_seq_ops;
+
+/*
+ * If the buffer is full, seq_printf can be called again, but it
+ * does nothing.  So, the these printing routines periodically check
+ * seq_has_overflowed to avoid wasting too much time trying to print to
+ * a full buffer.
+ */
+
+static int table_seq_show(struct seq_file *seq, void *iter_ptr)
+{
+	struct dlm_rsb *rsb = list_entry(iter_ptr, struct dlm_rsb, res_slow_list);
+
+	if (seq->op == &format1_seq_ops)
+		print_format1(rsb, seq);
+	else if (seq->op == &format2_seq_ops)
+		print_format2(rsb, seq);
+	else if (seq->op == &format3_seq_ops)
+		print_format3(rsb, seq);
+	else if (seq->op == &format4_seq_ops)
+		print_format4(rsb, seq);
+
+	return 0;
+}
+
+static void *table_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	struct dlm_ls *ls = seq->private;
+	struct list_head *list;
+
+	if (!*pos) {
+		if (seq->op == &format2_seq_ops)
+			seq_puts(seq, "id nodeid remid pid xid exflags flags sts grmode rqmode time_ms r_nodeid r_len r_name\n");
+		else if (seq->op == &format3_seq_ops)
+			seq_puts(seq, "rsb ptr nodeid first_lkid flags !root_list_empty !recover_list_empty recover_locks_count len\n");
+		else if (seq->op == &format4_seq_ops)
+			seq_puts(seq, "rsb ptr nodeid master_nodeid dir_nodeid our_nodeid toss_time flags len str|hex name\n");
+	}
+
+	if (seq->op == &format4_seq_ops)
+		list = &ls->ls_slow_inactive;
+	else
+		list = &ls->ls_slow_active;
+
+	read_lock_bh(&ls->ls_rsbtbl_lock);
+	return seq_list_start(list, *pos);
+}
+
+static void *table_seq_next(struct seq_file *seq, void *iter_ptr, loff_t *pos)
+{
+	struct dlm_ls *ls = seq->private;
+	struct list_head *list;
+
+	if (seq->op == &format4_seq_ops)
+		list = &ls->ls_slow_inactive;
+	else
+		list = &ls->ls_slow_active;
+
+	return seq_list_next(iter_ptr, list, pos);
+}
+
+static void table_seq_stop(struct seq_file *seq, void *iter_ptr)
+{
+	struct dlm_ls *ls = seq->private;
+
+	read_unlock_bh(&ls->ls_rsbtbl_lock);
+}
+
+static const struct seq_operations format1_seq_ops = {
+	.start = table_seq_start,
+	.next  = table_seq_next,
+	.stop  = table_seq_stop,
+	.show  = table_seq_show,
+};
+
+static const struct seq_operations format2_seq_ops = {
+	.start = table_seq_start,
+	.next  = table_seq_next,
+	.stop  = table_seq_stop,
+	.show  = table_seq_show,
+};
+
+static const struct seq_operations format3_seq_ops = {
+	.start = table_seq_start,
+	.next  = table_seq_next,
+	.stop  = table_seq_stop,
+	.show  = table_seq_show,
+};
+
+static const struct seq_operations format4_seq_ops = {
+	.start = table_seq_start,
+	.next  = table_seq_next,
+	.stop  = table_seq_stop,
+	.show  = table_seq_show,
+};
+
+static const struct file_operations format1_fops;
+static const struct file_operations format2_fops;
+static const struct file_operations format3_fops;
+static const struct file_operations format4_fops;
+
+static int table_open1(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq;
+	int ret;
+
+	ret = seq_open(file, &format1_seq_ops);
+	if (ret)
+		return ret;
+
+	seq = file->private_data;
+	seq->private = inode->i_private; /* the dlm_ls */
+	return 0;
+}
+
+static int table_open2(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq;
+	int ret;
+
+	ret = seq_open(file, &format2_seq_ops);
+	if (ret)
+		return ret;
+
+	seq = file->private_data;
+	seq->private = inode->i_private; /* the dlm_ls */
+	return 0;
+}
+
+static ssize_t table_write2(struct file *file, const char __user *user_buf,
+			    size_t count, loff_t *ppos)
+{
+	struct seq_file *seq = file->private_data;
+	int n, len, lkb_nodeid, lkb_status, error;
+	char name[DLM_RESNAME_MAXLEN + 1] = {};
+	struct dlm_ls *ls = seq->private;
+	unsigned int lkb_flags;
+	char buf[256] = {};
+	uint32_t lkb_id;
+
+	if (copy_from_user(buf, user_buf,
+			   min_t(size_t, sizeof(buf) - 1, count)))
+		return -EFAULT;
+
+	n = sscanf(buf, "%x %" __stringify(DLM_RESNAME_MAXLEN) "s %x %d %d",
+		   &lkb_id, name, &lkb_flags, &lkb_nodeid, &lkb_status);
+	if (n != 5)
+		return -EINVAL;
+
+	len = strnlen(name, DLM_RESNAME_MAXLEN);
+	error = dlm_debug_add_lkb(ls, lkb_id, name, len, lkb_flags,
+				  lkb_nodeid, lkb_status);
+	if (error)
+		return error;
+
+	return count;
+}
+
+static int table_open3(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq;
+	int ret;
+
+	ret = seq_open(file, &format3_seq_ops);
+	if (ret)
+		return ret;
+
+	seq = file->private_data;
+	seq->private = inode->i_private; /* the dlm_ls */
+	return 0;
+}
+
+static int table_open4(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq;
+	int ret;
+
+	ret = seq_open(file, &format4_seq_ops);
+	if (ret)
+		return ret;
+
+	seq = file->private_data;
+	seq->private = inode->i_private; /* the dlm_ls */
+	return 0;
+}
+
+static const struct file_operations format1_fops = {
+	.owner   = THIS_MODULE,
+	.open    = table_open1,
+	.read    = seq_read,
+	.llseek  = seq_lseek,
+	.release = seq_release
+};
+
+static const struct file_operations format2_fops = {
+	.owner   = THIS_MODULE,
+	.open    = table_open2,
+	.read    = seq_read,
+	.write   = table_write2,
+	.llseek  = seq_lseek,
+	.release = seq_release
+};
+
+static const struct file_operations format3_fops = {
+	.owner   = THIS_MODULE,
+	.open    = table_open3,
+	.read    = seq_read,
+	.llseek  = seq_lseek,
+	.release = seq_release
+};
+
+static const struct file_operations format4_fops = {
+	.owner   = THIS_MODULE,
+	.open    = table_open4,
+	.read    = seq_read,
+	.llseek  = seq_lseek,
+	.release = seq_release
+};
+
+/*
+ * dump lkb's on the ls_waiters list
+ */
+static ssize_t waiters_read(struct file *file, char __user *userbuf,
+			    size_t count, loff_t *ppos)
+{
+	struct dlm_ls *ls = file->private_data;
+	struct dlm_lkb *lkb;
+	size_t len = DLM_DEBUG_BUF_LEN, pos = 0, ret, rv;
+
+	mutex_lock(&debug_buf_lock);
+	ret = dlm_lock_recovery_try(ls);
+	if (!ret) {
+		rv = -EAGAIN;
+		goto out;
+	}
+
+	spin_lock_bh(&ls->ls_waiters_lock);
+	memset(debug_buf, 0, sizeof(debug_buf));
+
+	list_for_each_entry(lkb, &ls->ls_waiters, lkb_wait_reply) {
+		ret = snprintf(debug_buf + pos, len - pos, "%x %d %d %s\n",
+			       lkb->lkb_id, lkb->lkb_wait_type,
+			       lkb->lkb_nodeid, lkb->lkb_resource->res_name);
+		if (ret >= len - pos)
+			break;
+		pos += ret;
+	}
+	spin_unlock_bh(&ls->ls_waiters_lock);
+	dlm_unlock_recovery(ls);
+
+	rv = simple_read_from_buffer(userbuf, count, ppos, debug_buf, pos);
+out:
+	mutex_unlock(&debug_buf_lock);
+	return rv;
+}
+
+static ssize_t waiters_write(struct file *file, const char __user *user_buf,
+			     size_t count, loff_t *ppos)
+{
+	struct dlm_ls *ls = file->private_data;
+	int mstype, to_nodeid;
+	char buf[128] = {};
+	uint32_t lkb_id;
+	int n, error;
+
+	if (copy_from_user(buf, user_buf,
+			   min_t(size_t, sizeof(buf) - 1, count)))
+		return -EFAULT;
+
+	n = sscanf(buf, "%x %d %d", &lkb_id, &mstype, &to_nodeid);
+	if (n != 3)
+		return -EINVAL;
+
+	error = dlm_lock_recovery_try(ls);
+	if (!error)
+		return -EAGAIN;
+
+	error = dlm_debug_add_lkb_to_waiters(ls, lkb_id, mstype, to_nodeid);
+	dlm_unlock_recovery(ls);
+	if (error)
+		return error;
+
+	return count;
+}
+
+static const struct file_operations waiters_fops = {
+	.owner   = THIS_MODULE,
+	.open    = simple_open,
+	.read    = waiters_read,
+	.write   = waiters_write,
+	.llseek  = default_llseek,
+};
+
+void dlm_delete_debug_file(struct dlm_ls *ls)
+{
+	debugfs_remove(ls->ls_debug_rsb_dentry);
+	debugfs_remove(ls->ls_debug_waiters_dentry);
+	debugfs_remove(ls->ls_debug_locks_dentry);
+	debugfs_remove(ls->ls_debug_all_dentry);
+	debugfs_remove(ls->ls_debug_toss_dentry);
+	debugfs_remove(ls->ls_debug_queued_asts_dentry);
+}
+
+static int dlm_state_show(struct seq_file *file, void *offset)
+{
+	seq_printf(file, "%s\n", dlm_midcomms_state(file->private));
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(dlm_state);
+
+static int dlm_flags_show(struct seq_file *file, void *offset)
+{
+	seq_printf(file, "%lu\n", dlm_midcomms_flags(file->private));
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(dlm_flags);
+
+static int dlm_send_queue_cnt_show(struct seq_file *file, void *offset)
+{
+	seq_printf(file, "%d\n", dlm_midcomms_send_queue_cnt(file->private));
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(dlm_send_queue_cnt);
+
+static int dlm_version_show(struct seq_file *file, void *offset)
+{
+	seq_printf(file, "0x%08x\n", dlm_midcomms_version(file->private));
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(dlm_version);
+
+static ssize_t dlm_rawmsg_write(struct file *fp, const char __user *user_buf,
+				size_t count, loff_t *ppos)
+{
+	void *buf;
+	int ret;
+
+	if (count > PAGE_SIZE || count < sizeof(struct dlm_header))
+		return -EINVAL;
+
+	buf = kmalloc(PAGE_SIZE, GFP_NOFS);
+	if (!buf)
+		return -ENOMEM;
+
+	if (copy_from_user(buf, user_buf, count)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	ret = dlm_midcomms_rawmsg_send(fp->private_data, buf, count);
+	if (ret)
+		goto out;
+
+	kfree(buf);
+	return count;
+
+out:
+	kfree(buf);
+	return ret;
+}
+
+static const struct file_operations dlm_rawmsg_fops = {
+	.open	= simple_open,
+	.write	= dlm_rawmsg_write,
+};
+
+void *dlm_create_debug_comms_file(int nodeid, void *data)
+{
+	struct dentry *d_node;
+	char name[256];
+
+	memset(name, 0, sizeof(name));
+	snprintf(name, 256, "%d", nodeid);
+
+	d_node = debugfs_create_dir(name, dlm_comms);
+	debugfs_create_file("state", 0444, d_node, data, &dlm_state_fops);
+	debugfs_create_file("flags", 0444, d_node, data, &dlm_flags_fops);
+	debugfs_create_file("send_queue_count", 0444, d_node, data,
+			    &dlm_send_queue_cnt_fops);
+	debugfs_create_file("version", 0444, d_node, data, &dlm_version_fops);
+	debugfs_create_file("rawmsg", 0200, d_node, data, &dlm_rawmsg_fops);
+
+	return d_node;
+}
+
+void dlm_delete_debug_comms_file(void *ctx)
+{
+	debugfs_remove(ctx);
+}
+
+void dlm_create_debug_file(struct dlm_ls *ls)
+{
+	/* Reserve enough space for the longest file name */
+	char name[DLM_LOCKSPACE_LEN + sizeof("_queued_asts")];
+
+	/* format 1 */
+
+	ls->ls_debug_rsb_dentry = debugfs_create_file(ls->ls_name,
+						      S_IFREG | S_IRUGO,
+						      dlm_root,
+						      ls,
+						      &format1_fops);
+
+	/* format 2 */
+
+	snprintf(name, sizeof(name), "%s_locks", ls->ls_name);
+
+	ls->ls_debug_locks_dentry = debugfs_create_file(name,
+							0644,
+							dlm_root,
+							ls,
+							&format2_fops);
+
+	/* format 3 */
+
+	snprintf(name, sizeof(name), "%s_all", ls->ls_name);
+
+	ls->ls_debug_all_dentry = debugfs_create_file(name,
+						      S_IFREG | S_IRUGO,
+						      dlm_root,
+						      ls,
+						      &format3_fops);
+
+	/* format 4 */
+
+	snprintf(name, sizeof(name), "%s_toss", ls->ls_name);
+
+	ls->ls_debug_toss_dentry = debugfs_create_file(name,
+						       S_IFREG | S_IRUGO,
+						       dlm_root,
+						       ls,
+						       &format4_fops);
+
+	snprintf(name, sizeof(name), "%s_waiters", ls->ls_name);
+
+	ls->ls_debug_waiters_dentry = debugfs_create_file(name,
+							  0644,
+							  dlm_root,
+							  ls,
+							  &waiters_fops);
+}
+
+void __init dlm_register_debugfs(void)
+{
+	mutex_init(&debug_buf_lock);
+	dlm_root = debugfs_create_dir("dlm", NULL);
+	dlm_comms = debugfs_create_dir("comms", dlm_root);
+}
+
+void dlm_unregister_debugfs(void)
+{
+	debugfs_remove(dlm_root);
+}
+