linux-kernel - Re: [PATCH v2 0/6] tracing: open/delete fixes

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Message-ID: <20130728183407.GA16723@redhat.com>
Date:	Sun, 28 Jul 2013 20:34:07 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Alexander Z Lam <azl@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	David Sharp <dhsharp@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/6] tracing: open/delete fixes

On 07/26, Oleg Nesterov wrote:
>
> Testing: seems to work, but assumes that debugs was fixed too. Hopefully
> "debugfs: debugfs_remove_recursive() must not rely on list_empty(d_subdirs)"
> is fine.
>
> (We should probably make debugfs_remove_recursive() to return the error
>  and trace_events.c should warn if it fails)
>
> However: I am still testing this patches, so this is still mostly for
> review. I'll report if I find anything,

I tried to play more with these patches, and didn't find anything wrong.

However, after I re-read 6/6 I think it should be updated:

	- remove_event_file_dir() needs to check file->dir != NULL

	  it can be NULL if event_create_dir()->debugfs_create_dir()
	  fails, or if event_create_dir() fails before.

	- I've also added spin_lock(d_lock) and d_inode != NULL check.

	  I do not think this is needed. Afaics __create_file() can't
	  leave the !debugfs_positive() file on ->d_subdirs list if
	  debugfs_get_inode() fails, dput()->d_kill() should remove it.

	  But I do not understand this code enough, and debugfs checks
	  d_inode != NULL all the time.

I am sending "PATCH v3 6/6" in reply to "PATCH v2 6/6". See the diff
below.

So I am waiting for your review. If you and Masami agree with these
changes I'll resend other fixes (1 from me and 2 from Steven) on top
of this series.

Oleg.

--- x/kernel/trace/trace_events.c
+++ x/kernel/trace/trace_events.c
@@ -431,12 +431,18 @@ static void remove_event_file_dir(struct
 	struct dentry *dir = file->dir;
 	struct dentry *child;
 
-	/* ->i_mutex is not needed, nobody can create/remove a file */
-	list_for_each_entry(child, &dir->d_subdirs, d_u.d_child)
-		child->d_inode->i_private = NULL;
+	if (dir) {
+		spin_lock(&dir->d_lock);	/* probably unneeded */
+		list_for_each_entry(child, &dir->d_subdirs, d_u.d_child) {
+			if (child->d_inode)	/* probably unneeded */
+				child->d_inode->i_private = NULL;
+		}
+		spin_unlock(&dir->d_lock);
+
+		debugfs_remove_recursive(dir);
+	}
 
 	list_del(&file->list);
-	debugfs_remove_recursive(dir);
 	remove_subsystem(file->system);
 	kmem_cache_free(file_cachep, file);
 }

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