linux-kernel - Re: [PATCH] UML: UBD: Fix for processes stuck in D state forever in UserModeLinux

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Date:	Sat, 23 Aug 2014 17:34:37 +0200
From:	Richard Weinberger <richard@....at>
To:	Thorsten Knabe <linux@...rsten-knabe.de>
CC:	linux-kernel@...r.kernel.org, Thomas Meyer <thomas@...3r.de>,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH] UML: UBD: Fix for processes stuck in D state forever
 in UserModeLinux

Hi!

Am 23.08.2014 15:47, schrieb Thorsten Knabe:
> From: Thorsten Knabe <linux@...rsten-knabe.de>
> 
> UML: UBD: Fix for processes stuck in D state forever in UserModeLinux.
> 
> Starting with Linux 3.12 processes get stuck in D state forever in
> UserModeLinux under sync heavy workloads. This bug was introduced by
> commit 805f11a0d5 (um: ubd: Add REQ_FLUSH suppport).
> Fix bug by adding a check if FLUSH request was successfully submitted to
> the I/O thread and keeping the FLUSH request on the request queue on
> submission failures.
> 
> Fixes: 805f11a0d5 (um: ubd: Add REQ_FLUSH suppport)
> Signed-off-by: Thorsten Knabe <linux@...rsten-knabe.de>

Thanks a lot for hunting this issue down.

> ---
> Patch applies to 3.16.1.
> 
> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
> index 3716e69..b7d2840 100644
> --- a/arch/um/drivers/ubd_kern.c
> +++ b/arch/um/drivers/ubd_kern.c
> @@ -1277,7 +1277,7 @@ static void do_ubd_request(struct request_queue *q)
> 
>  	while(1){
>  		struct ubd *dev = q->queuedata;
> -		if(dev->end_sg == 0){
> +		if(dev->request == NULL){

Why do we need this specific change?

Thanks,
//richard
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