linux-kernel - Re: [PATCH 1/1]: Thaws refrigerated bdi flusher threads before invoking kthread

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Message-Id: <200911111259.04481.rjw@sisk.pl>
Date:	Wed, 11 Nov 2009 12:59:04 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	romit@...com, "jens.axboe@...cle.com" <jens.axboe@...cle.com>
Cc:	Pavel Machek <pavel@....cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH 1/1]: Thaws refrigerated bdi flusher threads before invoking kthread_stop on them

On Wednesday 11 November 2009, Romit Dasgupta wrote:
> Hello Rafael, 
>               As suggested I have added the relevant information in the
> changelog. The patch is below:
> > For completness, below is the information from the Romit's introductory message
> > (Romit, I really think that should go into the chagelog):
> 
> Kicks out frozen bdi flusher task out of the refrigerator when the said task
> needs to exit.
> Steps to reproduce this.
> 1) Mount a file system from MMC/SD card.
> 2) Unmount the file system. This creates a flusher task.
> 3) Attempt suspend to RAM. System is unresponsive.
> 
> This is because the bdi flusher thread is already in the refrigerator and will
> remain so until it is thawed. The MMC driver suspend routine ultimately will
> issue a 'kthread_stop' on the bdi flusher thread and will block until the
> flusher thread is exited. Since the bdi flusher thread is in the refrigerator
> it never cleans up until thawed.
> 
> Signed-off-by: Romit Dasgupta <romit@...com>

Thanks!  I'd still like to know that this change is fine with Jens, though.

Rafael


> ---
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 5a37e20..c757b05 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -606,8 +606,11 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
>  	 * Finally, kill the kernel threads. We don't need to be RCU
>  	 * safe anymore, since the bdi is gone from visibility.
>  	 */
> -	list_for_each_entry(wb, &bdi->wb_list, list)
> +	list_for_each_entry(wb, &bdi->wb_list, list) {
> +		if (unlikely(frozen(wb->task)))
> +			wb->task->flags &= ~PF_FROZEN;
>  		kthread_stop(wb->task);
> +	}
>  }
>  
>  void bdi_unregister(struct backing_dev_info *bdi)
--
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