Re: [patch 2/4] cdrom/aztcd: remove sleep_on() usage

[Johannes Stezenbach]

domen@xxxxxxxxxxxx wrote:
> From: Nishanth Aravamudan <nacc@xxxxxxxxxx>
> 
> 
> 
> Directly use wait-queues instead of the deprecated sleep_on().
> This required adding a local waitqueue. Patch is compile-tested.

IMHO this patch doesn't improve anything, it just makes the
code harder to read. sleep_on() is deprecated because there's
an inherent race between sleep_on() and wake_up(). To address
this you need to add a condition variable (e.g. AztStenLow) and
convert the code to use wait_event().
The timer trick used here makes it pretty hard to hit the
race, but with a preemptible kernel one could be preempted
between the SET_TIMER() and the sleep_on().

Johannes

> Signed-off-by: Nishanth Aravamudan <nacc@xxxxxxxxxx>
> Signed-off-by: Domen Puncer <domen@xxxxxxxxxxxx>
> ---
>  aztcd.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletion(-)
> 
> Index: quilt/drivers/cdrom/aztcd.c
> ===================================================================
> --- quilt.orig/drivers/cdrom/aztcd.c
> +++ quilt/drivers/cdrom/aztcd.c
> @@ -179,6 +179,7 @@
>  #include <linux/ioport.h>
>  #include <linux/string.h>
>  #include <linux/major.h>
> +#include <linux/wait.h>
>  
>  #include <linux/init.h>
>  
> @@ -429,9 +430,12 @@ static void dten_low(void)
>  #define STEN_LOW_WAIT   statusAzt()
>  static void statusAzt(void)
>  {
> +	DEFINE_WAIT(wait);
>  	AztTimeout = AZT_STATUS_DELAY;
>  	SET_TIMER(aztStatTimer, HZ / 100);
> -	sleep_on(&azt_waitq);
> +	prepare_to_wait(&azt_waitq, &wait, TASK_UNINTERRUPTIBLE);
> +	schedule();
> +	finish_wait(&azt_waitq, &wait);
>  	if (AztTimeout <= 0)
>  		printk("aztcd: Error Wait STEN_LOW_WAIT command:%x\n",
>  		       aztCmd);
> 
-
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