linux-kernel - Re: [linus:master] [eventfs] 852e46e239: BUG:unable_to_handle_page_fault_for

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Message-ID: <20240129120125.605e97af@gandalf.local.home>
Date: Mon, 29 Jan 2024 12:01:25 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
 lkp@...el.com, linux-kernel@...r.kernel.org, Masami Hiramatsu
 <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, Christian Brauner
 <brauner@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Ajay Kaher
 <ajay.kaher@...adcom.com>, linux-trace-kernel@...r.kernel.org
Subject: Re: [linus:master] [eventfs] 852e46e239:
 BUG:unable_to_handle_page_fault_for_address

On Sun, 28 Jan 2024 20:36:12 -0800
Linus Torvalds <torvalds@...ux-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