Re: [KJ] [PATCH 2.6.14-rc5 1/1] drivers/block/acsi_slm.c: replace

[Nishanth Aravamudan <nacc@us.ibm.com>]

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On 25.10.2005 [21:44:09 -0500], Irwan Djajadi wrote:
> Nishanth Aravamudan wrote:
> >On 24.10.2005 [18:46:01 -0500], Irwan Djajadi wrote:
> >
> >>Alexey Dobriyan wrote:
> >>
> >>
> >>>On Sat, Oct 22, 2005 at 09:53:51PM -0500, irwan.djajadi@iname.com wrote:
> >>>
> >>>
> >>>
> >>>>drivers/block/acsi_slm.c: replace interruptible_sleep_on() with
> >>>>wait_event_interruptible()
> >>>> 
> >>>>
> >>>
> >>>
> >>>
> >>>>--- 2.6.14-rc5/drivers/block/acsi_slm.c
> >>>>+++ mod/drivers/block/acsi_slm.c
> >>>>@@ -627,7 +627,7 @@ static ssize_t slm_write( struct file *f
> >>>>
> >>>>	while( SLMState == PRINTING ||
> >>>>		   (SLMState == FILLING && SLMBufOwner != device) ) {
> >>>>-		interruptible_sleep_on( &slm_wait );
> >>>>+		wait_event_interruptible( slm_wait, SLMState==IDLE );
> >>>>		if (signal_pending(current))
> >>>>			return( -ERESTARTSYS );
> >>>>	}
> >>>> 
> >>>>
> >>>
> >>>acsi_slm_replace_interruptible_sleep_on_with_wait_event_interruptible.patch
> >>
> >>>from -kj looks more correct.
> >>
> >>>From: Nishanth Aravamudan
> >>>
> >>>Use wait_event_interruptible() instead of the deprecated
> >>>interruptible_sleep_on(). The sleep_on() call later in the same
> >>>function is replaced with inline wait-queue code which achieves the
> >>>same. This required adding a local wait-queue, though.
> >>>
> >>>--- a/drivers/block/acsi_slm.c
> >>>+++ b/drivers/block/acsi_slm.c
> >>>@@ -625,12 +626,10 @@ static ssize_t slm_write( struct file *f
> >>>	int		device = iminor(node);
> >>>	int		n, filled, w, h;
> >>>
> >>>-	while( SLMState == PRINTING ||
> >>>-		   (SLMState == FILLING && SLMBufOwner != device) ) {
> >>>-		interruptible_sleep_on( &slm_wait );
> >>>-		if (signal_pending(current))
> >>>-			return( -ERESTARTSYS );
> >>>-	}
> >>>+	wait_event_interruptible(slm_wait, (SLMState != PRINTING &&
> >>>+				(SLMState != FILLING || SLMBufOwner == 
> >>>device)));
> >>>+	if (signal_pending(current))
> >>>+		return -ERESTARTSYS;
> >>>	if (SLMState == IDLE) {
> >>>		/* first data of page: get current page size  */
> >>>		if (slm_get_pagesize( device, &w, &h ))
> >>>
> >>>
> >>>
> >>
> >>That does look more correct. Please ignore my patch.
> >>Thanks!
> >
> >
> >@Irwan:
> >
> >Have you tested any of the patches you are sending? I stopped replacing
> >the *sleep_on*() family of functions once I was outside of the domain of
> >trivial substitution.
> >
> >You can't simply s/interruptible_sleep_on/wait_event_interruptible/ as
> >in many places the sleep_on() caller is not a loop, but one-time sleep!
> >I have noticed at least one case of this in the patches you are sending
> >out, but will try to make a more complete analysis soon.
> >
> >@Alexey:
> >
> >Be very careful pulling in these patches. I don't think any of the
> >remaining *sleep_on*() replacements are easy or trivial (at least the
> >ones w/o patches already in -KJ). I'll try to take a look more in depth
> >soon.
> >
> >Thanks,
> >Nish
> >
> 
> Hi Nish,
> 
> I only compile-test most of my patch over the weekend.. There are some 
> that I didn't even do compile test on because it's for a different 
> platform (I'm on x86). But yes, I am aware that some of *sleep_on*() 
> family function fixes are not trivial. I only changed ones that I 
> thought trivial. When the end-wait-condition is not clear to me, I left 
> it alone, and I went to the next.

It's not just the wait-condition, it's also the surrounding code
(including how the wait-queue gets woken).

[ On a sidenote: it took me a while to drive this through my own thick
skull, but the *most* important thing to do with KJ patches is
compile-test. If you don't have the arch at hand, get a cross-compiler,
I know there are guides for setting one up around. ]

> Maybe I'm missing something here, but I don't really see why 
> interruptible_sleep_on() or wait_event_interruptible() is not a straight 
> substitution when the caller is not in a loop..

First of all, there's the straightforward semantic difference between
sleeping on a wait queue and waiting for an event! Second, because the
caller is not in a loop, you are introducing a *new* loop by using
wait_event*(). That may not be desired. Depends on the condition you
put in, as well.

> interruptible_sleep_on() does not have a loop inside, and it's a single 
> incantation of wait. When it wakes up, it could be because of a signal 
> or end-condition.

Or someone manually waking up the wait-queue. There is no "end
condition" with sleep_on().

> I see that wait_event_interruptible() has a check outside and a loop 
> inside to ensure that when it returns it's because of a signal or 
> end-condition. (So it's a more correct version of interruptible_sleep_on())

Right, so whereas with sleep_on, waking-up the wait-queue is sufficient
to terminate the sleep, it is *not* for wait_event() -- either the event
*must* be satisfied or a signal *must* have arrived for wait_event() to
return.

> The semantic looks the same to me, so why can't it be a straight 
> substitution when the end-wait-condition is straightforward?
> 
> I don't intend to inject bugs, so I appreciate y'all's review of my 
> patches, and let me know/smack me when I do dumb things.

I appreciate the effort. Getting rid of sleep_on() & co. would be a nice
benefit IMO (or getting it closer to the point where we can mark them
deprecated).

Thanks,
Nish

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