linux-kernel - Re: which signal is sent to freeze process?

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Message-Id: <200707232125.09070.rjw@sisk.pl>
Date:	Mon, 23 Jul 2007 21:25:08 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Agarwal, Lomesh" <lomesh.agarwal@...el.com>
Cc:	nigel@...pend2.net, linux-kernel@...r.kernel.org,
	Pavel Machek <pavel@....cz>
Subject: Re: which signal is sent to freeze process?

On Monday, 23 July 2007 20:38, Agarwal, Lomesh wrote:
> The other problem I am facing that read from socket returns with ENODATA
> when resuming. any ideas?

It's of similar kind: the system call checks signal_pending(current) and exit
with an error if that's true.

Well, I'm afraid we can't place try_to_freeze() in every system call that
does something like that ...

Greetings,
Rafael


> -----Original Message-----
> From: Rafael J. Wysocki [mailto:rjw@...k.pl] 
> Sent: Friday, July 20, 2007 3:10 PM
> To: Agarwal, Lomesh
> Cc: nigel@...pend2.net; linux-kernel@...r.kernel.org
> Subject: Re: which signal is sent to freeze process?
> 
> On Friday, 20 July 2007 20:07, Agarwal, Lomesh wrote:
> > Can you suggest a way I can debug the issue why I am getting EINTR
> error
> > for system calls in resuming? What else can cause the system call
> > failure with EINTR?
> 
> Well, I think I know what the problem is.  do_poll checks
> signal_pending(current) and breaks when it's set, but that may be caused
> by the freezer.
> 
> You may try the patch below (untested) and see if that helps.
> 
> Greetings,
> Rafael
> 
> 
> ---
>  fs/select.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.22-rc6-mm1/fs/select.c
> ===================================================================
> --- linux-2.6.22-rc6-mm1.orig/fs/select.c
> +++ linux-2.6.22-rc6-mm1/fs/select.c
> @@ -23,6 +23,7 @@
>  #include <linux/file.h>
>  #include <linux/fs.h>
>  #include <linux/rcupdate.h>
> +#include <linux/freezer.h>
>  
>  #include <asm/uaccess.h>
>  
> @@ -593,6 +594,8 @@ static int do_poll(unsigned int nfds,  s
>  		struct poll_list *walk;
>  		long __timeout;
>  
> +		try_to_freeze();
> +
>  		set_current_state(TASK_INTERRUPTIBLE);
>  		for (walk = list; walk != NULL; walk = walk->next) {
>  			struct pollfd * pfd, * pfd_end;
> @@ -618,7 +621,8 @@ static int do_poll(unsigned int nfds,  s
>  		 * a poll_table to them on the next loop iteration.
>  		 */
>  		pt = NULL;
> -		if (count || !*timeout || signal_pending(current))
> +		if (count || !*timeout ||
> +		    (signal_pending(current) && !freezing(current)))
>  			break;
>  		count = wait->error;
>  		if (count)
> 
> 

-- 
"Premature optimization is the root of all evil." - Donald Knuth
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