Re: [linus:master] [eventfs] 852e46e239: BUG:unable_to_handle_page_fault_for_address

From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: kernel test robot <oliver.sang@intel.com>,
	oe-lkp@lists.linux.dev, lkp@intel.com,
	linux-kernel@vger.kernel.org,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Christian Brauner <brauner@kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Ajay Kaher <ajay.kaher@broadcom.com>,
	linux-trace-kernel@vger.kernel.org
Subject: Re: [linus:master] [eventfs] 852e46e239: BUG:unable_to_handle_page_fault_for_address
Date: Mon, 29 Jan 2024 12:01:25 -0500	[thread overview]
Message-ID: <20240129120125.605e97af@gandalf.local.home> (raw)
In-Reply-To: <CAHk-=wh0M=e8R=ZXxa4vesLTtvGmYWJ-w1VmXxW5Mva=Nimk4Q@mail.gmail.com>

On Sun, 28 Jan 2024 20:36:12 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> End result: the d_instantiate() needs to be done *after* the inode has
> been fully filled in.
> 
> Alternatively, you could
> 
>  (a) not drop the eventfs_mutex around the create_dir() call
> 
>  (b) take the eventfs_mutex around all of set_top_events_ownership()
> 
> and just fix it by having the lock protect the lack of ordering.

Hi Linus,

Thanks for the analysis. I have a patch that removes the dropping of the
mutex over the create_dir/file() calls, and lockdep hasn't complained about
it.

I was going to add that to my queue for the next merge window along with
other clean ups but this looks like it actually fixes a real bug. I'll move
that over to my urgent queue and start testing it.

-- Steve