Re: [PATCH 3/8] PM: suspend_block: Abort task freezing if a suspend_blocker is active.

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Wednesday 15 April 2009, Arve Hjønnevåg wrote:
> If a suspend_blocker is active, suspend will fail anyway. Since
> try_to_freeze_tasks can take up to 20 seconds to complete or fail, aborting
> as soon as someone blocks suspend (e.g. from an interrupt handler) improves
> the worst case wakeup latency.
> 
> On an older kernel where task freezing could fail for processes attached
> to a debugger, this fixed a problem where the device sometimes hung for
> 20 seconds before the screen turned on.
> 
> Signed-off-by: Arve Hjønnevåg <arve@android.com>
> ---
>  kernel/power/process.c |   23 ++++++++++++++++++-----
>  1 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index ca63401..76d7cdb 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -13,6 +13,7 @@
>  #include <linux/module.h>
>  #include <linux/syscalls.h>
>  #include <linux/freezer.h>
> +#include <linux/suspend_block.h>
>  
>  /* 
>   * Timeout for stopping processes
> @@ -36,6 +37,7 @@ static int try_to_freeze_tasks(bool sig_only)
>  	struct timeval start, end;
>  	u64 elapsed_csecs64;
>  	unsigned int elapsed_csecs;
> +	unsigned int wakeup = 0;

Make it a bool, please.

>  	do_gettimeofday(&start);
>  
> @@ -62,6 +64,10 @@ static int try_to_freeze_tasks(bool sig_only)
>  		} while_each_thread(g, p);
>  		read_unlock(&tasklist_lock);
>  		yield();			/* Yield is okay here */
> +		if (todo && suspend_is_blocked()) {
> +			wakeup = 1;

'true', please.

> +			break;
> +		}
>  		if (time_after(jiffies, end_time))
>  			break;
>  	} while (todo);
> @@ -77,11 +83,18 @@ static int try_to_freeze_tasks(bool sig_only)
>  		 * and caller must call thaw_processes() if something fails),
>  		 * but it cleans up leftover PF_FREEZE requests.
>  		 */
> -		printk("\n");
> -		printk(KERN_ERR "Freezing of tasks failed after %d.%02d seconds "
> -				"(%d tasks refusing to freeze):\n",
> -				elapsed_csecs / 100, elapsed_csecs % 100, todo);
> -		show_state();
> +		if (wakeup) {
> +			printk("\n");

Why is the separate printk() necessary ?

> +			printk(KERN_ERR "Freezing of %s aborted\n",
> +					sig_only ? "user space " : "tasks ");
> +		} else {
> +			printk("\n");

Why is the separate printk() necessary ?

> +			printk(KERN_ERR
> +			       "Freezing of tasks failed after %d.%02d seconds "
> +			       "(%d tasks refusing to freeze):\n",
> +			       elapsed_csecs / 100, elapsed_csecs % 100, todo);
> +			show_state();
> +		}
>  		read_lock(&tasklist_lock);
>  		do_each_thread(g, p) {
>  			task_lock(p);


-- 
Everyone knows that debugging is twice as hard as writing a program
in the first place.  So if you're as clever as you can be when you write it,
how will you ever debug it? --- Brian Kernighan
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