linux-kernel - Re: [PATCH] relay: move remove_buf_file inside relay_close

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Message-ID: <87y5c0mrad.fsf@openvz.org>
Date:	Tue, 30 Apr 2013 11:06:02 +0400
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, gregkh@...uxfoundation.org,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH] relay: move remove_buf_file inside relay_close_buf PING..

On Mon, 22 Apr 2013 11:57:52 +0400, Dmitry Monakhov <dmonakhov@...nvz.org> wrote:
Non-text part: multipart/mixed
> 
Seriously. Am I an only one who use blktrace?
Jens can you please take it?
> Hi,
> Let someone please finally take care of this patch.
> Originally it was submitted here https://lkml.org/lkml/2010/2/28/103
> This patch fix very annoying issue. I've got OK from Jens and Tom
> Zanussi but no one accept it. MAINTAINERS file has no info about relayfs.
> So I've added to CC all people which may be interested in that.
> 
> From 1c0d96aece60a8a81c3f0cf1f681a5ff4333a2ff Mon Sep 17 00:00:00 2001
> From: Dmitry Monakhov <dmonakhov@...nvz.org>
> Date: Mon, 22 Apr 2013 11:41:41 +0400
> Subject: [PATCH] relay: move remove_buf_file inside relay_close_buf
> 
> Currently remove_buf_file callback is called from from kobject
> release method. This result in follow issue:
> # blktrace -d /dev/sda1 -d /dev/sda -o test
> 
> blktrace_setup()
>  dir = create_dir()
>  rchan = relay_open(dir,...)
>  ->create_buf_file_callback
>     buf_file  = debugfs_create_file(dir, )
> 
> Userspace will open buf_file.
> Later we make a decision to stop tracing
> blktrace_down()
>   relay_close(rhcan)  /* just decrement kobj reference  */
>                       /* since it is not zero then callback not called */
>   debugfs_remove(dir) /* FAIL due to non empty dir   */
> 
> Later user space will close the file and file will be deleted,
> but directory still exist.
> user_space_close()
>  ->file_release
>    ->release_buf_file_callback
>      ->debugfs_remove(buf_file
> ## TESTCASE:
> # blktrace -d /dev/sda1 -d /dev/sda -o test
> # After that blktrace infrastructure will remain broken in
> # an unusable state so: blktrace -d /dev/sda1 will not work.
> 
> In fact this is general issue, blktrace is just one of examples.
> We can not reliably remove parent dir until all users close the
> buf_file.
> 
> Solution: We don't have to wait that long. File should be deleted inside
> relay_close_buf().
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
> Acked-by : Jens Axboe <axboe@...nel.dk>
> 
> ---
>  kernel/relay.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/relay.c b/kernel/relay.c
> index 01ab081..a0d2000 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -234,7 +234,6 @@ static void relay_destroy_buf(struct rchan_buf *buf)
>  static void relay_remove_buf(struct kref *kref)
>  {
>  	struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
> -	buf->chan->cb->remove_buf_file(buf->dentry);
>  	relay_destroy_buf(buf);
>  }
>  
> @@ -484,6 +483,7 @@ static void relay_close_buf(struct rchan_buf *buf)
>  {
>  	buf->finalized = 1;
>  	del_timer_sync(&buf->timer);
> +	buf->chan->cb->remove_buf_file(buf->dentry);
>  	kref_put(&buf->kref, relay_remove_buf);
>  }
>  
> -- 
> 1.7.1
> 
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