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Date: Tue, 28 Sep 2004 09:21:23 +0200
From: Ingo Molnar <mingo@elte.hu>
To: "J.A. Magallon" <jamagallon@able.es>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>, tytso@mit.edu
Subject: Re: Stack traces in 2.6.9-rc2-mm4
Message-ID: <20040928072123.GA15177@elte.hu>
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* J.A. Magallon <jamagallon@able.es> wrote:

> I got the same on another place...
> 
> Sep 28 00:48:51 werewolf kernel: using smp_processor_id() in preemptible 
> code: X/4012
> Sep 28 00:48:51 werewolf kernel:  [smp_processor_id+135/141] 
> smp_processor_id+0x87/0x8d
> Sep 28 00:48:51 werewolf kernel:  [add_timer_randomness+314/365] 
> add_timer_randomness+0x13a/0x16d
> Sep 28 00:48:51 werewolf kernel:  [<b0206733>] 
> add_timer_randomness+0x13a/0x16d
> Sep 28 00:48:51 werewolf kernel:  [input_event+85/999] 
> input_event+0x55/0x3e7

the one below should fix this: a certain codepath in the random driver
relied on vt_ioctl() being under the BKL and implicitly disabling
preemption. The code wasnt buggy upstream but it's slighly unrobust so i
think we want the fix upstream too, independently of the remove-bkl
patch. This change has been in the -VP patchset for some time so it
should work fine.

	Ingo

--- linux/drivers/char/random.c.orig	
+++ linux/drivers/char/random.c	
@@ -807,10 +807,11 @@ static void add_timer_randomness(struct 
 	long		delta, delta2, delta3;
 	int		entropy = 0;
 
+	preempt_disable();
 	/* if over the trickle threshold, use only 1 in 4096 samples */
 	if ( random_state->entropy_count > trickle_thresh &&
 	     (__get_cpu_var(trickle_count)++ & 0xfff))
-		return;
+		goto out;
 
 	/*
 	 * Use get_cycles() if implemented, otherwise fall back to
@@ -861,6 +862,8 @@ static void add_timer_randomness(struct 
 		entropy = int_ln_12bits(delta);
 	}
 	batch_entropy_store(num, time, entropy);
+out:
+	preempt_enable();
 }
 
 void add_keyboard_randomness(unsigned char scancode)
-
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