linux-kernel - Re: [PATCH v2] eventfs: Test for ei->is

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Date:   Mon, 30 Oct 2023 10:41:27 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux trace kernel <linux-trace-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Arnd Bergmann <arnd@...db.de>,
        "Naresh Kamboju <naresh.kamboju@...aro.org>, Beau Belgrave
        <beaub@...ux.microsoft.com>, Ajay Kaher <akaher@...are.com>, Andrew
        Morton" <akpm@...ux-foundation.org>, lkft-triage@...ts.linaro.org
Subject: Re: [PATCH v2] eventfs: Test for ei->is_freed when accessing
 ei->dentry

On Mon, 30 Oct 2023 12:37:08 +0530
Naresh Kamboju <naresh.kamboju@...aro.org> wrote:

> 
> I have tested the linux-trace.git trace/core and run selftests ftrace
> the reported kernel panic [1] & [2] has been fixed but found

Good to know. Can I add "Tested-by" from you for that bug fix?

> "general protection fault"  at  kernel/trace/trace_events.c:2439.

Can you test with the below patch?

Also, can I ask what are you testing this on that makes it trigger so
easily? As I'm not able to trigger these in my tests, even though they are
indeed bugs.

-- Steve

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 7ad7496bd597..7a0b54ddda24 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -609,7 +609,13 @@ static struct dentry *eventfs_root_lookup(struct inode *dir,
 		entry = &ei->entries[i];
 		if (strcmp(name, entry->name) == 0) {
 			void *cdata = data;
-			r = entry->callback(name, &mode, &cdata, &fops);
+			mutex_lock(&eventfs_mutex);
+			/* If ei->is_freed, then the event itself may be too */
+			if (!ei->is_freed)
+				r = entry->callback(name, &mode, &cdata, &fops);
+			else
+				r = -1;
+			mutex_unlock(&eventfs_mutex);
 			if (r <= 0)
 				continue;
 			ret = simple_lookup(dir, dentry, flags);
@@ -743,7 +749,13 @@ static int dcache_dir_open_wrapper(struct inode *inode, struct file *file)
 		void *cdata = data;
 		entry = &ei->entries[i];
 		name = entry->name;
-		r = entry->callback(name, &mode, &cdata, &fops);
+		mutex_lock(&eventfs_mutex);
+		/* If ei->is_freed, then the event itself may be too */
+		if (!ei->is_freed)
+			r = entry->callback(name, &mode, &cdata, &fops);
+		else
+			r = -1;
+		mutex_unlock(&eventfs_mutex);
 		if (r <= 0)
 			continue;
 		d = create_file_dentry(ei, i, parent, name, mode, cdata, fops, false);