linux-kernel - Re: [PATCH] tracefs: Remove unneeded buggy tracefs iput callback

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Message-ID: <20240522140548.40dbd49b@gandalf.local.home>
Date: Wed, 22 May 2024 14:05:48 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH] tracefs: Remove unneeded buggy tracefs iput callback

On Wed, 22 May 2024 12:45:04 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> The iput callback was added because the remount could call into the
> eventfs code and touch the ei->entry_attrs array, which could have been
> freed when an eventfs directory is freed (via a synthetic event). But the
> entry_attrs was freed incorrectly and since been fixed to be freed after
> the last reference of the ei is done.
> 
> The iput clears the TRACEFS_EVENT_INODE flag of the tracefs_inode
> preventing it from calling the eventfs_remount() function. But the iput
> can be called after the last reference to the inode is done but the
> eventfs_inode still exists, causing the eventfs_remount() not to be called
> on an tracefs_inode when it should be.

Testing this more, I found that the iput is still needed, as the deletion
of the eventfs inodes can happen before the inode is released.

Will produce a v2 that handles this properly.

-- Steve