Re: PROBLEM: Bug in __pollwait() can cause select() and poll() to hang in 2.4.22-pre2 -- second try

[Rusty Russell <rusty@rustcorp.com.au>]

In message <Pine.LNX.4.44.0306302114170.2186-100000@home.osdl.org> you write:
> 
> On Tue, 1 Jul 2003, Rusty Russell wrote:
> > 
> > Linus?  See thread below: poll_wait is called with task state !=
> > TASK_RUNNING, but can do a yield on low memory, causing eternal hangs.
> 
> Hint: 2.5.x does not have this problem, because the yield() in 2.5.x isn't
> buggy.
> 
> So the proper fix is to just fix yield() on 2.4.x.

Thanks Linus.

Um, Ray?  2.4's yield also does:

	void yield(void)
	{
		set_current_state(TASK_RUNNING);
		sys_sched_yield();
		schedule();
	}

So how did the below patch make any difference?

Now thoroughly confused,
Rusty.

--- linux-2.4.22-pre2.orig/mm/page_alloc.c      Thu Nov 28 17:53:15 2002
+++ linux-2.4.22-pre2/mm/page_alloc.c   Fri Jun 27 13:47:49 2003
@@ -418,6 +418,7 @@
                 return NULL;

         /* Yield for kswapd, and try again */
+        set_current_state(TASK_RUNNING);
         yield();
         goto rebalance;
  }

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.