[PATCH v3 09/10] eventfs: moving tracing/events to eventfs

[PATCH v3 09/10] eventfs: moving tracing/events to eventfs

[Ajay Kaher]

Till now /sys/kernel/debug/tracing/events is a part of tracefs,
with-in this patch creating 'events' and it's sub-dir as eventfs.
Basically replacing tracefs calls with eventfs calls for 'events'.

Signed-off-by: Ajay Kaher <akaher@vmware.com>
Co-developed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Tested-by: Ching-lin Yu <chinglinyu@google.com>
---
 fs/tracefs/inode.c           | 18 ++++++++++
 include/linux/trace_events.h |  1 +
 kernel/trace/trace.h         |  2 +-
 kernel/trace/trace_events.c  | 67 +++++++++++++++++++-----------------
 4 files changed, 55 insertions(+), 33 deletions(-)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 76820d3e9..a098d7153 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -374,6 +374,23 @@ static const struct super_operations tracefs_super_operations = {
 	.show_options	= tracefs_show_options,
 };
 
+static void tracefs_dentry_iput(struct dentry *dentry, struct inode *inode)
+{
+	struct tracefs_inode *ti;
+
+	if (!dentry || !inode)
+		return;
+
+	ti = get_tracefs(inode);
+	if (ti && ti->flags & TRACEFS_EVENT_INODE)
+		eventfs_set_ef_status_free(dentry);
+	iput(inode);
+}
+
+static const struct dentry_operations tracefs_dentry_operations = {
+	.d_iput = tracefs_dentry_iput,
+};
+
 static int trace_fill_super(struct super_block *sb, void *data, int silent)
 {
 	static const struct tree_descr trace_files[] = {{""}};
@@ -396,6 +413,7 @@ static int trace_fill_super(struct super_block *sb, void *data, int silent)
 		goto fail;
 
 	sb->s_op = &tracefs_super_operations;
+	sb->s_d_op = &tracefs_dentry_operations;
 
 	tracefs_apply_options(sb, false);
 
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 0e373222a..696843d46 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -635,6 +635,7 @@ struct trace_event_file {
 	struct list_head		list;
 	struct trace_event_call		*event_call;
 	struct event_filter __rcu	*filter;
+	struct eventfs_file             *ef;
 	struct dentry			*dir;
 	struct trace_array		*tr;
 	struct trace_subsystem_dir	*system;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b895c3346..b265ae2df 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1310,7 +1310,7 @@ struct trace_subsystem_dir {
 	struct list_head		list;
 	struct event_subsystem		*subsystem;
 	struct trace_array		*tr;
-	struct dentry			*entry;
+	struct eventfs_file             *ef;
 	int				ref_count;
 	int				nr_events;
 };
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 16bc5ba45..94aa6f9c9 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -988,7 +988,8 @@ static void remove_subsystem(struct trace_subsystem_dir *dir)
 		return;
 
 	if (!--dir->nr_events) {
-		tracefs_remove(dir->entry);
+		if (dir->ef)
+			eventfs_remove(dir->ef);
 		list_del(&dir->list);
 		__put_system_dir(dir);
 	}
@@ -1009,7 +1010,8 @@ static void remove_event_file_dir(struct trace_event_file *file)
 
 		tracefs_remove(dir);
 	}
-
+	if (file->ef)
+		eventfs_remove(file->ef);
 	list_del(&file->list);
 	remove_subsystem(file->system);
 	free_event_filter(file->filter);
@@ -2295,13 +2297,13 @@ create_new_subsystem(const char *name)
 	return NULL;
 }
 
-static struct dentry *
+static struct eventfs_file *
 event_subsystem_dir(struct trace_array *tr, const char *name,
 		    struct trace_event_file *file, struct dentry *parent)
 {
 	struct event_subsystem *system, *iter;
 	struct trace_subsystem_dir *dir;
-	struct dentry *entry;
+	int res;
 
 	/* First see if we did not already create this dir */
 	list_for_each_entry(dir, &tr->systems, list) {
@@ -2309,7 +2311,7 @@ event_subsystem_dir(struct trace_array *tr, const char *name,
 		if (strcmp(system->name, name) == 0) {
 			dir->nr_events++;
 			file->system = dir;
-			return dir->entry;
+			return dir->ef;
 		}
 	}
 
@@ -2333,8 +2335,8 @@ event_subsystem_dir(struct trace_array *tr, const char *name,
 	} else
 		__get_system(system);
 
-	dir->entry = tracefs_create_dir(name, parent);
-	if (!dir->entry) {
+	dir->ef = eventfs_add_subsystem_dir(name, parent, &tr->eventfs_rwsem);
+	if (IS_ERR(dir->ef)) {
 		pr_warn("Failed to create system directory %s\n", name);
 		__put_system(system);
 		goto out_free;
@@ -2349,22 +2351,22 @@ event_subsystem_dir(struct trace_array *tr, const char *name,
 	/* the ftrace system is special, do not create enable or filter files */
 	if (strcmp(name, "ftrace") != 0) {
 
-		entry = tracefs_create_file("filter", TRACE_MODE_WRITE,
-					    dir->entry, dir,
+		res = eventfs_add_file("filter", TRACE_MODE_WRITE,
+					    dir->ef, dir,
 					    &ftrace_subsystem_filter_fops);
-		if (!entry) {
+		if (res) {
 			kfree(system->filter);
 			system->filter = NULL;
 			pr_warn("Could not create tracefs '%s/filter' entry\n", name);
 		}
 
-		trace_create_file("enable", TRACE_MODE_WRITE, dir->entry, dir,
+		eventfs_add_file("enable", TRACE_MODE_WRITE, dir->ef, dir,
 				  &ftrace_system_enable_fops);
 	}
 
 	list_add(&dir->list, &tr->systems);
 
-	return dir->entry;
+	return dir->ef;
 
  out_free:
 	kfree(dir);
@@ -2418,7 +2420,7 @@ event_create_dir(struct dentry *parent, struct trace_event_file *file)
 {
 	struct trace_event_call *call = file->event_call;
 	struct trace_array *tr = file->tr;
-	struct dentry *d_events;
+	struct eventfs_file *ef_subsystem = NULL;
 	const char *name;
 	int ret;
 
@@ -2430,24 +2432,24 @@ event_create_dir(struct dentry *parent, struct trace_event_file *file)
 	if (WARN_ON_ONCE(strcmp(call->class->system, TRACE_SYSTEM) == 0))
 		return -ENODEV;
 
-	d_events = event_subsystem_dir(tr, call->class->system, file, parent);
-	if (!d_events)
+	ef_subsystem = event_subsystem_dir(tr, call->class->system, file, parent);
+	if (!ef_subsystem)
 		return -ENOMEM;
 
 	name = trace_event_name(call);
-	file->dir = tracefs_create_dir(name, d_events);
-	if (!file->dir) {
+	file->ef = eventfs_add_dir(name, ef_subsystem, &tr->eventfs_rwsem);
+	if (IS_ERR(file->ef)) {
 		pr_warn("Could not create tracefs '%s' directory\n", name);
 		return -1;
 	}
 
 	if (call->class->reg && !(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE))
-		trace_create_file("enable", TRACE_MODE_WRITE, file->dir, file,
+		eventfs_add_file("enable", TRACE_MODE_WRITE, file->ef, file,
 				  &ftrace_enable_fops);
 
 #ifdef CONFIG_PERF_EVENTS
 	if (call->event.type && call->class->reg)
-		trace_create_file("id", TRACE_MODE_READ, file->dir,
+		eventfs_add_file("id", TRACE_MODE_READ, file->ef,
 				  (void *)(long)call->event.type,
 				  &ftrace_event_id_fops);
 #endif
@@ -2463,27 +2465,27 @@ event_create_dir(struct dentry *parent, struct trace_event_file *file)
 	 * triggers or filters.
 	 */
 	if (!(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE)) {
-		trace_create_file("filter", TRACE_MODE_WRITE, file->dir,
+		eventfs_add_file("filter", TRACE_MODE_WRITE, file->ef,
 				  file, &ftrace_event_filter_fops);
 
-		trace_create_file("trigger", TRACE_MODE_WRITE, file->dir,
+		eventfs_add_file("trigger", TRACE_MODE_WRITE, file->ef,
 				  file, &event_trigger_fops);
 	}
 
 #ifdef CONFIG_HIST_TRIGGERS
-	trace_create_file("hist", TRACE_MODE_READ, file->dir, file,
+	eventfs_add_file("hist", TRACE_MODE_READ, file->ef, file,
 			  &event_hist_fops);
 #endif
 #ifdef CONFIG_HIST_TRIGGERS_DEBUG
-	trace_create_file("hist_debug", TRACE_MODE_READ, file->dir, file,
+	eventfs_add_file("hist_debug", TRACE_MODE_READ, file->ef, file,
 			  &event_hist_debug_fops);
 #endif
-	trace_create_file("format", TRACE_MODE_READ, file->dir, call,
+	eventfs_add_file("format", TRACE_MODE_READ, file->ef, call,
 			  &ftrace_event_format_fops);
 
 #ifdef CONFIG_TRACE_EVENT_INJECT
 	if (call->event.type && call->class->reg)
-		trace_create_file("inject", 0200, file->dir, file,
+		eventfs_add_file("inject", 0200, file->ef, file,
 				  &event_inject_fops);
 #endif
 
@@ -3636,21 +3638,22 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr)
 {
 	struct dentry *d_events;
 	struct dentry *entry;
+	int error = 0;
 
 	entry = trace_create_file("set_event", TRACE_MODE_WRITE, parent,
 				  tr, &ftrace_set_event_fops);
 	if (!entry)
 		return -ENOMEM;
 
-	d_events = tracefs_create_dir("events", parent);
-	if (!d_events) {
+	d_events = eventfs_create_events_dir("events", parent, &tr->eventfs_rwsem);
+	if (IS_ERR(d_events)) {
 		pr_warn("Could not create tracefs 'events' directory\n");
 		return -ENOMEM;
 	}
 
-	entry = trace_create_file("enable", TRACE_MODE_WRITE, d_events,
+	error = eventfs_add_top_file("enable", TRACE_MODE_WRITE, d_events,
 				  tr, &ftrace_tr_enable_fops);
-	if (!entry)
+	if (error)
 		return -ENOMEM;
 
 	/* There are not as crucial, just warn if they are not created */
@@ -3663,11 +3666,11 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr)
 			  &ftrace_set_event_notrace_pid_fops);
 
 	/* ring buffer internal formats */
-	trace_create_file("header_page", TRACE_MODE_READ, d_events,
+	eventfs_add_top_file("header_page", TRACE_MODE_READ, d_events,
 				  ring_buffer_print_page_header,
 				  &ftrace_show_header_fops);
 
-	trace_create_file("header_event", TRACE_MODE_READ, d_events,
+	eventfs_add_top_file("header_event", TRACE_MODE_READ, d_events,
 				  ring_buffer_print_entry_header,
 				  &ftrace_show_header_fops);
 
@@ -3755,7 +3758,7 @@ int event_trace_del_tracer(struct trace_array *tr)
 
 	down_write(&trace_event_sem);
 	__trace_remove_event_dirs(tr);
-	tracefs_remove(tr->event_dir);
+	eventfs_remove_events_dir(tr->event_dir);
 	up_write(&trace_event_sem);
 
 	tr->event_dir = NULL;
-- 
2.40.0

Re: [PATCH v3 09/10] eventfs: moving tracing/events to eventfs

[Ajay Kaher]

> Hello,
>
> kernel test robot noticed "WARNING:possible_circular_locking_dependency_detected" on:
>
> commit: a3bb763435d444023d3bca5479da632c57724619 ("[PATCH v3 09/10] eventfs: moving tracing/events to eventfs")
> url: https://github.com/intel-lab-lkp/linux/commits/Ajay-Kaher/tracing-Require-all-trace-events-to-have-a-TRACE_SYSTEM/20230601-230657
> base: https://git.kernel.org/cgit/linux/kernel/git/shuah/linux-kselftest.git next
> patch link: 1685610013-33478-10-git-send-email-akaher@vmware.com/">https://lore.kernel.org/all/1685610013-33478-10-git-send-email-akaher@vmware.com/
> patch subject: [PATCH v3 09/10] eventfs: moving tracing/events to eventfs
>
> in testcase: kernel-selftests
> version: kernel-selftests-x86_64-60acb023-1_20230329
> with following parameters:
>
> group: ftrace
>
> test-description: The kernel contains a set of "self tests" under the tools/testing/selftests/ directory. These are intended to be small unit tests to exercise individual code paths in the kernel.
> test-url: https://www.kernel.org/doc/Documentation/kselftest.txt
>
>
> compiler: gcc-12
> test machine: 36 threads 1 sockets Intel(R) Core(TM) i9-10980XE CPU @ 3.00GHz (Cascade Lake) with 32G memory
>
> (please refer to attached dmesg/kmsg for entire log/backtrace)
>
>
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <oliver.sang@intel.com>
> | Closes: 202306102230.b5aa258d-oliver.sang@intel.com">https://lore.kernel.org/oe-lkp/202306102230.b5aa258d-oliver.sang@intel.com
>
>
> kern  :warn  : [  173.884312] WARNING: possible circular locking dependency detected
> kern  :warn  : [  173.884947] 6.4.0-rc1-00014-ga3bb763435d4 #1 Not tainted
> kern  :warn  : [  173.885501] ------------------------------------------------------
> kern  :warn  : [  173.886125] ftracetest/2186 is trying to acquire lock:
> kern :warn : [  173.886665] ffff88810045d368 (&sb->s_type->i_mutex_key#5){++++}-{3:3}, at: dcache_dir_open_wrapper (fs/tracefs/event_inode.c:373)
> kern  :warn  : [  173.887638]
> but task is already holding lock:
> kern :warn : [  173.888299] ffffffff84e6d640 (eventfs_rwsem/1){.+.+}-{3:3}, at: dcache_dir_open_wrapper (fs/tracefs/event_inode.c:364)
> kern  :warn  : [  173.889183]
> which lock already depends on the new lock.
>
> kern  :warn  : [  173.890101]
> the existing dependency chain (in reverse order) is:
> kern  :warn  : [  173.890898]
> -> #1 (eventfs_rwsem/1){.+.+}-{3:3}:
> kern :warn : [  173.891600] lock_acquire (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5693 kernel/locking/lockdep.c:5656)
> kern :warn : [  173.892066] down_read_nested (kernel/locking/rwsem.c:1263 kernel/locking/rwsem.c:1646)
> kern :warn : [  173.892553] eventfs_root_lookup (fs/tracefs/event_inode.c:283)
> kern :warn : [  173.893058] __lookup_slow (include/linux/dcache.h:359 include/linux/dcache.h:364 fs/namei.c:1691)
> kern :warn : [  173.893529] walk_component (include/linux/fs.h:790 fs/namei.c:1708 fs/namei.c:1998)
> kern :warn : [  173.894006] path_lookupat (fs/namei.c:2455 fs/namei.c:2479)
> kern :warn : [  173.894476] filename_lookup (fs/namei.c:2508)
> kern :warn : [  173.894974] vfs_statx (fs/stat.c:239)
> kern :warn : [  173.895410] vfs_fstatat (fs/stat.c:277)
> kern :warn : [  173.895851] __do_sys_newfstatat (fs/stat.c:447)
> kern :warn : [  173.896350] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> kern :warn : [  173.896815] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
> kern  :warn  : [  173.897392]
> -> #0 (&sb->s_type->i_mutex_key#5){++++}-{3:3}:
> kern :warn : [  173.898158] check_prev_add (kernel/locking/lockdep.c:3109)
> kern :warn : [  173.898643] __lock_acquire (kernel/locking/lockdep.c:3228 kernel/locking/lockdep.c:3842 kernel/locking/lockdep.c:5074)
> kern :warn : [  173.899133] lock_acquire (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5693 kernel/locking/lockdep.c:5656)
> kern :warn : [  173.899610] down_write (arch/x86/include/asm/preempt.h:80 kernel/locking/rwsem.c:1304 kernel/locking/rwsem.c:1315 kernel/locking/rwsem.c:1574)
> kern :warn : [  173.900054] dcache_dir_open_wrapper (fs/tracefs/event_inode.c:373)
> kern :warn : [  173.900603] do_dentry_open (fs/open.c:920)
> kern :warn : [  173.901081] do_open (fs/namei.c:3636)
> kern :warn : [  173.901508] path_openat (fs/namei.c:3792)
> kern :warn : [  173.901963] do_filp_open (fs/namei.c:3818)
> kern :warn : [  173.902425] do_sys_openat2 (fs/open.c:1356)
> kern :warn : [  173.902902] __x64_sys_openat (fs/open.c:1383)
> kern :warn : [  173.903408] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> kern :warn : [  173.903864] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
> kern  :warn  : [  173.904451]
> other info that might help us debug this:
>
> kern  :warn  : [  173.905372]  Possible unsafe locking scenario:
>
> kern  :warn  : [  173.906049]        CPU0                    CPU1
> kern  :warn  : [  173.906538]        ----                    ----
> kern  :warn  : [  173.907027]   rlock(eventfs_rwsem/1);
> kern  :warn  : [  173.907464]                                lock(&sb->s_type->i_mutex_key#5);
> kern  :warn  : [  173.908171]                                lock(eventfs_rwsem/1);
> kern  :warn  : [  173.908800]   lock(&sb->s_type->i_mutex_key#5);
> kern  :warn  : [  173.909291]
> *** DEADLOCK ***

Steve, this seems not to be a problem here as dcache_dir_open_wrapper()
and eventfs_root_lookup() both lock eventfs_rwsem as read lock, however
it’s known problem in Lockdep for rwlock:
https://lpc.events/event/2/contributions/74/
And available patchset on Lockdep not upstreamed:
https://lore.kernel.org/all/20190829083132.22394-1-duyuyang@gmail.com/

-Ajay