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Date:      Thu, 26 Jan 2012 07:39:50 +0400
From:      Andrey Chernov <ache@FreeBSD.ORG>
To:        Mark Murray <markm@FreeBSD.ORG>, David Schultz <das@FreeBSD.ORG>, src-committers@FreeBSD.ORG, svn-src-all@FreeBSD.ORG, svn-src-head@FreeBSD.ORG
Subject:   Re: svn commit: r230230 - head/sys/dev/random
Message-ID:  <20120126033950.GA80737@vniz.net>
In-Reply-To: <20120126030305.GA80493@vniz.net>
References:  <E1Rny2A-000C3x-O6@groundzero.grondar.org> <20120120055823.GA28177@vniz.net> <E1RoG98-000DiP-0Y@groundzero.grondar.org> <20120120215649.GA40016@vniz.net> <E1Rp0lq-000Gly-FT@groundzero.grondar.org> <20120122185545.GA11874@vniz.net> <E1Rp5Bn-000HBl-2P@groundzero.grondar.org> <20120125140237.GA74896@vniz.net> <E1Rq8Kn-000Ms9-KE@groundzero.grondar.org> <20120126030305.GA80493@vniz.net>

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On Thu, Jan 26, 2012 at 07:03:05AM +0400, Andrey Chernov wrote:
> On Wed, Jan 25, 2012 at 07:16:41PM +0000, Mark Murray wrote:
> > I thought you were going to do this as a function? It would be
> > slightly neater to do it that way.
> > 
> > Looks good! Are you sure this needs no locking or volatile
> > variables?
> 
> Now with function, volatile, atomic and even enum:

Sorry. Reading of state variable should be atomical too. Fixed version:

--- sys/libkern.h.old	2012-01-16 07:15:12.000000000 +0400
+++ sys/libkern.h	2012-01-26 06:01:51.000000000 +0400
@@ -72,6 +72,8 @@ static __inline quad_t qabs(quad_t a) { 
 
 /* Prototypes for non-quad routines. */
 struct malloc_type;
+enum 	arc4_is { ARC4_ENTR_NONE, ARC4_ENTR_HAVE, ARC4_ENTR_DONE };
+void	arc4rand_iniseed_state(enum arc4_is state);
 uint32_t arc4random(void);
 void	 arc4rand(void *ptr, u_int len, int reseed);
 int	 bcmp(const void *, const void *, size_t);
--- dev/random/randomdev_soft.c.old	2011-03-02 01:42:19.000000000 +0300
+++ dev/random/randomdev_soft.c	2012-01-26 06:04:05.000000000 +0400
@@ -366,6 +366,7 @@ random_yarrow_unblock(void)
 		selwakeuppri(&random_systat.rsel, PUSER);
 		wakeup(&random_systat);
 	}
+	arc4rand_iniseed_state(ARC4_ENTR_HAVE);
 }
 
 static int
--- libkern/arc4random.c.old	2008-08-08 01:51:09.000000000 +0400
+++ libkern/arc4random.c	2012-01-26 07:27:06.000000000 +0400
@@ -24,6 +24,7 @@ __FBSDID("$FreeBSD: src/sys/libkern/arc4
 #define	ARC4_RESEED_SECONDS 300
 #define	ARC4_KEYBYTES (256 / 8)
 
+static volatile enum arc4_is iniseed_state = ARC4_ENTR_NONE;
 static u_int8_t arc4_i, arc4_j;
 static int arc4_numruns = 0;
 static u_int8_t arc4_sbox[256];
@@ -74,6 +75,7 @@ arc4_randomstir (void)
 	/* Reset for next reseed cycle. */
 	arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS;
 	arc4_numruns = 0;
+	arc4rand_iniseed_state(ARC4_ENTR_DONE);
 
 	/*
 	 * Throw away the first N words of output, as suggested in the
@@ -103,6 +105,24 @@ arc4_init(void)
 
 SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL);
 
+void
+arc4rand_iniseed_state(enum arc4_is state)
+{
+	switch (state) {
+		case ARC4_ENTR_NONE:
+			atomic_store_rel_int(&iniseed_state, state);
+			break;
+		case ARC4_ENTR_HAVE:
+			if (atomic_load_acq_int(&iniseed_state) == ARC4_ENTR_NONE)
+				atomic_store_rel_int(&iniseed_state, state);
+			break;
+		case ARC4_ENTR_DONE:
+			if (atomic_load_acq_int(&iniseed_state) == ARC4_ENTR_HAVE)
+				atomic_store_rel_int(&iniseed_state, state);
+			break;
+	}
+}
+
 /*
  * Generate a random byte.
  */
@@ -130,7 +150,7 @@ arc4rand(void *ptr, u_int len, int resee
 	struct timeval tv;
 
 	getmicrouptime(&tv);
-	if (reseed || 
+	if (reseed || atomic_load_acq_int(&iniseed_state) == ARC4_ENTR_HAVE ||
 	   (arc4_numruns > ARC4_RESEED_BYTES) ||
 	   (tv.tv_sec > arc4_t_reseed))
 		arc4_randomstir();

-- 
http://ache.vniz.net/



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