diff mbox series

[v3,1/4] tracing/user_events: Prepare find/delete for same name events

Message ID 20240214175046.240-2-beaub@linux.microsoft.com
State New
Headers
Series tracing/user_events: Introduce multi-format events |

Commit Message

Beau Belgrave Feb. 14, 2024, 5:50 p.m. UTC 
  The current code for finding and deleting events assumes that there will
never be cases when user_events are registered with the same name, but
different formats. In the future this scenario will exist to ensure
user programs can be updated or modify their events and run different
versions of their programs side-by-side without being blocked.

This change does not yet allow for multi-format events. If user_events
are registered with the same name but different arguments the programs
see the same return values as before. This change simply makes it
possible to easily accomodate for this in future changes.

Update find_user_event() to take in argument parameters and register
flags to accomodate future multi-format event scenarios. Have find
validate argument matching and return error pointers to cover address
in use cases, or allocation errors. Update callers to handle error
pointer logic.

Move delete_user_event() to use hash walking directly now that find has
changed. Delete all events found that match the register name, stop
if an error occurs and report back to the user.

Update user_fields_match() to cover list_empty() scenarios instead of
each callsite doing it now that find_user_event() uses it directly.

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
---
 kernel/trace/trace_events_user.c | 107 +++++++++++++++++--------------
 1 file changed, 59 insertions(+), 48 deletions(-)

Comments

Beau Belgrave Feb. 21, 2024, 5:04 p.m. UTC | #1 
On Wed, Feb 21, 2024 at 10:17:21AM -0500, Steven Rostedt wrote:
> On Wed, 14 Feb 2024 17:50:43 +0000
> Beau Belgrave <beaub@linux.microsoft.com> wrote:
> 
> So the patches look good, but since I gave you some updates, I'm now going
> to go though "nits". Like grammar and such ;-)
> 

Sure thing.

> > The current code for finding and deleting events assumes that there will
> > never be cases when user_events are registered with the same name, but
> > different formats. In the future this scenario will exist to ensure
> 
> > user programs can be updated or modify their events and run different
> > versions of their programs side-by-side without being blocked.
> 
> Can you change the last sentence above. I read it three times and it's
> still awkward to understand it. Particularly, the "user programs can be
> updated or modify their events". That just doesn't want to compute.
> 

Yeah, I'll clean this up.

> > 
> > This change does not yet allow for multi-format events. If user_events
> > are registered with the same name but different arguments the programs
> > see the same return values as before. This change simply makes it
> > possible to easily accomodate for this in future changes.
> 
> I think you can drop the "in future changes" part.
> 

Agreed.

> > 
> > Update find_user_event() to take in argument parameters and register
> > flags to accomodate future multi-format event scenarios. Have find
> > validate argument matching and return error pointers to cover address
> > in use cases, or allocation errors. Update callers to handle error
> 
>   "to cover address in use cases" ?

Yeah, if the ABI is using a single-format event and it's already in use,
we return -EADDRINUSE. It does not happen in multi-format event cases,
since that is allowed.

I'll try to clarify this a bit.

> 
> > pointer logic.
> > 
> > Move delete_user_event() to use hash walking directly now that find has
> > changed. Delete all events found that match the register name, stop
> 
> "now that find has changed" ?  You mean the "find function"?
> 

Yeah, I'll just use the function name here, find_user_event().

> > if an error occurs and report back to the user.
> > 
> > Update user_fields_match() to cover list_empty() scenarios instead of
> > each callsite doing it now that find_user_event() uses it directly.
> 
> The above is a bit of a run-on sentence.
> 

I'll clean it up a bit.

Thanks,
-Beau

> -- Steve
> 
> > 
> > Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
> > ---
diff mbox series

Patch

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 9365ce407426..dda58681247e 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -202,6 +202,8 @@  static struct user_event_mm *user_event_mm_get(struct user_event_mm *mm);
 static struct user_event_mm *user_event_mm_get_all(struct user_event *user);
 static void user_event_mm_put(struct user_event_mm *mm);
 static int destroy_user_event(struct user_event *user);
+static bool user_fields_match(struct user_event *user, int argc,
+			      const char **argv);
 
 static u32 user_event_key(char *name)
 {
@@ -1493,17 +1495,24 @@  static int destroy_user_event(struct user_event *user)
 }
 
 static struct user_event *find_user_event(struct user_event_group *group,
-					  char *name, u32 *outkey)
+					  char *name, int argc, const char **argv,
+					  u32 flags, u32 *outkey)
 {
 	struct user_event *user;
 	u32 key = user_event_key(name);
 
 	*outkey = key;
 
-	hash_for_each_possible(group->register_table, user, node, key)
-		if (!strcmp(EVENT_NAME(user), name))
+	hash_for_each_possible(group->register_table, user, node, key) {
+		if (strcmp(EVENT_NAME(user), name))
+			continue;
+
+		if (user_fields_match(user, argc, argv))
 			return user_event_get(user);
 
+		return ERR_PTR(-EADDRINUSE);
+	}
+
 	return NULL;
 }
 
@@ -1860,6 +1869,9 @@  static bool user_fields_match(struct user_event *user, int argc,
 	struct list_head *head = &user->fields;
 	int i = 0;
 
+	if (argc == 0)
+		return list_empty(head);
+
 	list_for_each_entry_reverse(field, head, link) {
 		if (!user_field_match(field, argc, argv, &i))
 			return false;
@@ -1880,10 +1892,8 @@  static bool user_event_match(const char *system, const char *event,
 	match = strcmp(EVENT_NAME(user), event) == 0 &&
 		(!system || strcmp(system, USER_EVENTS_SYSTEM) == 0);
 
-	if (match && argc > 0)
+	if (match)
 		match = user_fields_match(user, argc, argv);
-	else if (match && argc == 0)
-		match = list_empty(&user->fields);
 
 	return match;
 }
@@ -1922,11 +1932,11 @@  static int user_event_parse(struct user_event_group *group, char *name,
 			    char *args, char *flags,
 			    struct user_event **newuser, int reg_flags)
 {
-	int ret;
-	u32 key;
 	struct user_event *user;
+	char **argv = NULL;
 	int argc = 0;
-	char **argv;
+	int ret;
+	u32 key;
 
 	/* Currently don't support any text based flags */
 	if (flags != NULL)
@@ -1935,41 +1945,34 @@  static int user_event_parse(struct user_event_group *group, char *name,
 	if (!user_event_capable(reg_flags))
 		return -EPERM;
 
+	if (args) {
+		argv = argv_split(GFP_KERNEL, args, &argc);
+
+		if (!argv)
+			return -ENOMEM;
+	}
+
 	/* Prevent dyn_event from racing */
 	mutex_lock(&event_mutex);
-	user = find_user_event(group, name, &key);
+	user = find_user_event(group, name, argc, (const char **)argv,
+			       reg_flags, &key);
 	mutex_unlock(&event_mutex);
 
-	if (user) {
-		if (args) {
-			argv = argv_split(GFP_KERNEL, args, &argc);
-			if (!argv) {
-				ret = -ENOMEM;
-				goto error;
-			}
+	if (argv)
+		argv_free(argv);
 
-			ret = user_fields_match(user, argc, (const char **)argv);
-			argv_free(argv);
-
-		} else
-			ret = list_empty(&user->fields);
-
-		if (ret) {
-			*newuser = user;
-			/*
-			 * Name is allocated by caller, free it since it already exists.
-			 * Caller only worries about failure cases for freeing.
-			 */
-			kfree(name);
-		} else {
-			ret = -EADDRINUSE;
-			goto error;
-		}
+	if (IS_ERR(user))
+		return PTR_ERR(user);
+
+	if (user) {
+		*newuser = user;
+		/*
+		 * Name is allocated by caller, free it since it already exists.
+		 * Caller only worries about failure cases for freeing.
+		 */
+		kfree(name);
 
 		return 0;
-error:
-		user_event_put(user, false);
-		return ret;
 	}
 
 	user = kzalloc(sizeof(*user), GFP_KERNEL_ACCOUNT);
@@ -2052,25 +2055,33 @@  static int user_event_parse(struct user_event_group *group, char *name,
 }
 
 /*
- * Deletes a previously created event if it is no longer being used.
+ * Deletes previously created events if they are no longer being used.
  */
 static int delete_user_event(struct user_event_group *group, char *name)
 {
-	u32 key;
-	struct user_event *user = find_user_event(group, name, &key);
+	struct user_event *user;
+	struct hlist_node *tmp;
+	u32 key = user_event_key(name);
+	int ret = -ENOENT;
 
-	if (!user)
-		return -ENOENT;
+	/* Attempt to delete all event(s) with the name passed in */
+	hash_for_each_possible_safe(group->register_table, user, tmp, node, key) {
+		if (strcmp(EVENT_NAME(user), name))
+			continue;
 
-	user_event_put(user, true);
+		if (!user_event_last_ref(user))
+			return -EBUSY;
 
-	if (!user_event_last_ref(user))
-		return -EBUSY;
+		if (!user_event_capable(user->reg_flags))
+			return -EPERM;
 
-	if (!user_event_capable(user->reg_flags))
-		return -EPERM;
+		ret = destroy_user_event(user);
 
-	return destroy_user_event(user);
+		if (ret)
+			goto out;
+	}
+out:
+	return ret;
 }
 
 /*