fs: dlm: initial support for tracepoints

This patch adds initial support for dlm tracepoints. It will introduce
tracepoints to dlm main functionality dlm_lock()/dlm_unlock() and their
complete ast() callback or blocking bast() callback.

The lock/unlock functionality has a start and end tracepoint, this is
because there exists a race in case if would have a tracepoint at the
end position only the complete/blocking callbacks could occur before. To
work with eBPF tracing and using their lookup hash functionality there
could be problems that an entry was not inserted yet. However use the
start functionality for hash insert and check again in end functionality
if there was an dlm internal error so there is no ast callback. In further
it might also that locks with local masters will occur those callbacks
immediately so we must have such functionality.

I did not make everything accessible yet, although it seems eBPF can be
used to access a lot of internal datastructures if it's aware of the
struct definitions of the running kernel instance. We still can change
it, if you do eBPF experiments e.g. time measurements between lock and
callback functionality you can simple use the local lkb_id field as hash
value in combination with the lockspace id if you have multiple
lockspaces. Otherwise you can simple use trace-cmd for some functionality,
e.g. `trace-cmd record -e dlm` and `trace-cmd report` afterwards.
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/ast.c

@@ -9,6 +9,8 @@
 *******************************************************************************
 ******************************************************************************/
 
+#include <trace/events/dlm.h>
+
 #include "dlm_internal.h"
 #include "lock.h"
 #include "user.h"
@@ -254,10 +256,12 @@ void dlm_callback_work(struct work_struct *work)
 			continue;
 		} else if (callbacks[i].flags & DLM_CB_BAST) {
 			bastfn(lkb->lkb_astparam, callbacks[i].mode);
+			trace_dlm_bast(ls, lkb, callbacks[i].mode);
 		} else if (callbacks[i].flags & DLM_CB_CAST) {
 			lkb->lkb_lksb->sb_status = callbacks[i].sb_status;
 			lkb->lkb_lksb->sb_flags = callbacks[i].sb_flags;
 			castfn(lkb->lkb_astparam);
+			trace_dlm_ast(ls, lkb, lkb->lkb_lksb);
 		}
 	}
 

fs/dlm/lock.c

@@ -53,6 +53,8 @@
                                    R: do_xxxx()
    L: receive_xxxx_reply()     <-  R: send_xxxx_reply()
 */
+#include <trace/events/dlm.h>
+
 #include <linux/types.h>
 #include <linux/rbtree.h>
 #include <linux/slab.h>
@@ -3437,6 +3439,8 @@ int dlm_lock(dlm_lockspace_t *lockspace,
 	if (error)
 		goto out;
 
+	trace_dlm_lock_start(ls, lkb, mode, flags);
+
 	error = set_lock_args(mode, lksb, flags, namelen, 0, ast,
 			      astarg, bast, &args);
 	if (error)
@@ -3450,6 +3454,8 @@ int dlm_lock(dlm_lockspace_t *lockspace,
 	if (error == -EINPROGRESS)
 		error = 0;
  out_put:
+	trace_dlm_lock_end(ls, lkb, mode, flags, error);
+
 	if (convert || error)
 		__put_lkb(ls, lkb);
 	if (error == -EAGAIN || error == -EDEADLK)
@@ -3481,6 +3487,8 @@ int dlm_unlock(dlm_lockspace_t *lockspace,
 	if (error)
 		goto out;
 
+	trace_dlm_unlock_start(ls, lkb, flags);
+
 	error = set_unlock_args(flags, astarg, &args);
 	if (error)
 		goto out_put;
@@ -3495,6 +3503,8 @@ int dlm_unlock(dlm_lockspace_t *lockspace,
 	if (error == -EBUSY && (flags & (DLM_LKF_CANCEL | DLM_LKF_FORCEUNLOCK)))
 		error = 0;
  out_put:
+	trace_dlm_unlock_end(ls, lkb, flags, error);
+
 	dlm_put_lkb(lkb);
  out:
 	dlm_unlock_recovery(ls);

fs/dlm/main.c

@@ -19,6 +19,9 @@
 #include "config.h"
 #include "lowcomms.h"
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/dlm.h>
+
 static int __init init_dlm(void)
 {
 	int error;

include/trace/events/dlm.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM dlm
+
+#if !defined(_TRACE_DLM_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_DLM_H
+
+#include <linux/dlm.h>
+#include <linux/dlmconstants.h>
+#include <linux/tracepoint.h>
+
+#include "../../../fs/dlm/dlm_internal.h"
+
+#define show_lock_flags(flags) __print_flags(flags, "|",	\
+	{ DLM_LKF_NOQUEUE,	"NOQUEUE" },			\
+	{ DLM_LKF_CANCEL,	"CANCEL" },			\
+	{ DLM_LKF_CONVERT,	"CONVERT" },			\
+	{ DLM_LKF_VALBLK,	"VALBLK" },			\
+	{ DLM_LKF_QUECVT,	"QUECVT" },			\
+	{ DLM_LKF_IVVALBLK,	"IVVALBLK" },			\
+	{ DLM_LKF_CONVDEADLK,	"CONVDEADLK" },			\
+	{ DLM_LKF_PERSISTENT,	"PERSISTENT" },			\
+	{ DLM_LKF_NODLCKWT,	"NODLCKWT" },			\
+	{ DLM_LKF_NODLCKBLK,	"NODLCKBLK" },			\
+	{ DLM_LKF_EXPEDITE,	"EXPEDITE" },			\
+	{ DLM_LKF_NOQUEUEBAST,	"NOQUEUEBAST" },		\
+	{ DLM_LKF_HEADQUE,	"HEADQUE" },			\
+	{ DLM_LKF_NOORDER,	"NOORDER" },			\
+	{ DLM_LKF_ORPHAN,	"ORPHAN" },			\
+	{ DLM_LKF_ALTPR,	"ALTPR" },			\
+	{ DLM_LKF_ALTCW,	"ALTCW" },			\
+	{ DLM_LKF_FORCEUNLOCK,	"FORCEUNLOCK" },		\
+	{ DLM_LKF_TIMEOUT,	"TIMEOUT" })
+
+#define show_lock_mode(mode) __print_symbolic(mode,		\
+	{ DLM_LOCK_IV,		"IV"},				\
+	{ DLM_LOCK_NL,		"NL"},				\
+	{ DLM_LOCK_CR,		"CR"},				\
+	{ DLM_LOCK_CW,		"CW"},				\
+	{ DLM_LOCK_PR,		"PR"},				\
+	{ DLM_LOCK_PW,		"PW"},				\
+	{ DLM_LOCK_EX,		"EX"})
+
+#define show_dlm_sb_flags(flags) __print_flags(flags, "|",	\
+	{ DLM_SBF_DEMOTED,	"DEMOTED" },			\
+	{ DLM_SBF_VALNOTVALID,	"VALNOTVALID" },		\
+	{ DLM_SBF_ALTMODE,	"ALTMODE" })
+
+/* note: we begin tracing dlm_lock_start() only if ls and lkb are found */
+TRACE_EVENT(dlm_lock_start,
+
+	TP_PROTO(struct dlm_ls *ls, struct dlm_lkb *lkb, int mode,
+		 __u32 flags),
+
+	TP_ARGS(ls, lkb, mode, flags),
+
+	TP_STRUCT__entry(
+		__field(__u32, ls_id)
+		__field(__u32, lkb_id)
+		__field(int, mode)
+		__field(__u32, flags)
+	),
+
+	TP_fast_assign(
+		__entry->ls_id = ls->ls_global_id;
+		__entry->lkb_id = lkb->lkb_id;
+		__entry->mode = mode;
+		__entry->flags = flags;
+	),
+
+	TP_printk("ls_id=%u lkb_id=%x mode=%s flags=%s",
+		  __entry->ls_id, __entry->lkb_id,
+		  show_lock_mode(__entry->mode),
+		  show_lock_flags(__entry->flags))
+
+);
+
+TRACE_EVENT(dlm_lock_end,
+
+	TP_PROTO(struct dlm_ls *ls, struct dlm_lkb *lkb, int mode, __u32 flags,
+		 int error),
+
+	TP_ARGS(ls, lkb, mode, flags, error),
+
+	TP_STRUCT__entry(
+		__field(__u32, ls_id)
+		__field(__u32, lkb_id)
+		__field(int, mode)
+		__field(__u32, flags)
+		__field(int, error)
+	),
+
+	TP_fast_assign(
+		__entry->ls_id = ls->ls_global_id;
+		__entry->lkb_id = lkb->lkb_id;
+		__entry->mode = mode;
+		__entry->flags = flags;
+
+		/* return value will be zeroed in those cases by dlm_lock()
+		 * we do it here again to not introduce more overhead if
+		 * trace isn't running and error reflects the return value.
+		 */
+		if (error == -EAGAIN || error == -EDEADLK)
+			__entry->error = 0;
+		else
+			__entry->error = error;
+	),
+
+	TP_printk("ls_id=%u lkb_id=%x mode=%s flags=%s error=%d",
+		  __entry->ls_id, __entry->lkb_id,
+		  show_lock_mode(__entry->mode),
+		  show_lock_flags(__entry->flags), __entry->error)
+
+);
+
+TRACE_EVENT(dlm_bast,
+
+	TP_PROTO(struct dlm_ls *ls, struct dlm_lkb *lkb, int mode),
+
+	TP_ARGS(ls, lkb, mode),
+
+	TP_STRUCT__entry(
+		__field(__u32, ls_id)
+		__field(__u32, lkb_id)
+		__field(int, mode)
+	),
+
+	TP_fast_assign(
+		__entry->ls_id = ls->ls_global_id;
+		__entry->lkb_id = lkb->lkb_id;
+		__entry->mode = mode;
+	),
+
+	TP_printk("ls_id=%u lkb_id=%x mode=%s", __entry->ls_id,
+		  __entry->lkb_id, show_lock_mode(__entry->mode))
+
+);
+
+TRACE_EVENT(dlm_ast,
+
+	TP_PROTO(struct dlm_ls *ls, struct dlm_lkb *lkb, struct dlm_lksb *lksb),
+
+	TP_ARGS(ls, lkb, lksb),
+
+	TP_STRUCT__entry(
+		__field(__u32, ls_id)
+		__field(__u32, lkb_id)
+		__field(u8, sb_flags)
+		__field(int, sb_status)
+	),
+
+	TP_fast_assign(
+		__entry->ls_id = ls->ls_global_id;
+		__entry->lkb_id = lkb->lkb_id;
+		__entry->sb_flags = lksb->sb_flags;
+		__entry->sb_status = lksb->sb_status;
+	),
+
+	TP_printk("ls_id=%u lkb_id=%x sb_flags=%s sb_status=%d",
+		  __entry->ls_id, __entry->lkb_id,
+		  show_dlm_sb_flags(__entry->sb_flags), __entry->sb_status)
+
+);
+
+/* note: we begin tracing dlm_unlock_start() only if ls and lkb are found */
+TRACE_EVENT(dlm_unlock_start,
+
+	TP_PROTO(struct dlm_ls *ls, struct dlm_lkb *lkb, __u32 flags),
+
+	TP_ARGS(ls, lkb, flags),
+
+	TP_STRUCT__entry(
+		__field(__u32, ls_id)
+		__field(__u32, lkb_id)
+		__field(__u32, flags)
+	),
+
+	TP_fast_assign(
+		__entry->ls_id = ls->ls_global_id;
+		__entry->lkb_id = lkb->lkb_id;
+		__entry->flags = flags;
+	),
+
+	TP_printk("ls_id=%u lkb_id=%x flags=%s",
+		  __entry->ls_id, __entry->lkb_id,
+		  show_lock_flags(__entry->flags))
+
+);
+
+TRACE_EVENT(dlm_unlock_end,
+
+	TP_PROTO(struct dlm_ls *ls, struct dlm_lkb *lkb, __u32 flags,
+		 int error),
+
+	TP_ARGS(ls, lkb, flags, error),
+
+	TP_STRUCT__entry(
+		__field(__u32, ls_id)
+		__field(__u32, lkb_id)
+		__field(__u32, flags)
+		__field(int, error)
+	),
+
+	TP_fast_assign(
+		__entry->ls_id = ls->ls_global_id;
+		__entry->lkb_id = lkb->lkb_id;
+		__entry->flags = flags;
+		__entry->error = error;
+	),
+
+	TP_printk("ls_id=%u lkb_id=%x flags=%s error=%d",
+		  __entry->ls_id, __entry->lkb_id,
+		  show_lock_flags(__entry->flags), __entry->error)
+
+);
+
+#endif /* if !defined(_TRACE_DLM_H) || defined(TRACE_HEADER_MULTI_READ) */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>