linux-kernel - [PATCH 6/6] sound/isa: convert nested spin_lock_irqsave to spin

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Message-ID: <Pine.LNX.4.64.0907181725540.26792@ask.diku.dk>
Date:	Sat, 18 Jul 2009 17:26:14 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	perex@...ex.cz, tiwai@...e.de, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH 6/6] sound/isa: convert nested spin_lock_irqsave to spin_lock

From: Julia Lawall <julia@...u.dk>

If spin_lock_irqsave is called twice in a row with the same second
argument, the interrupt state at the point of the second call overwrites
the value saved by the first call.  Indeed, the second call does not need
to save the interrupt state, so it is changed to a simple spin_lock.

The semantic match that finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
expression lock1,lock2;
expression flags;
@@

*spin_lock_irqsave(lock1,flags)
... when != flags
*spin_lock_irqsave(lock2,flags)
// </smpl>

Signed-off-by: Julia Lawall <julia@...u.dk>

---
 sound/isa/gus/gus_pcm.c             |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/isa/gus/gus_pcm.c b/sound/isa/gus/gus_pcm.c
index edb11ee..2dcf45b 100644
--- a/sound/isa/gus/gus_pcm.c
+++ b/sound/isa/gus/gus_pcm.c
@@ -795,13 +795,13 @@ static int snd_gf1_pcm_volume_put(struct snd_kcontrol *kcontrol, struct snd_ctl_
 		if (!(pcmp->flags & SNDRV_GF1_PCM_PFLG_ACTIVE))
 			continue;
 		/* load real volume - better precision */
-		spin_lock_irqsave(&gus->reg_lock, flags);
+		spin_lock(&gus->reg_lock);
 		snd_gf1_select_voice(gus, pvoice->number);
 		snd_gf1_ctrl_stop(gus, SNDRV_GF1_VB_VOLUME_CONTROL);
 		vol = pvoice == pcmp->pvoices[0] ? gus->gf1.pcm_volume_level_left : gus->gf1.pcm_volume_level_right;
 		snd_gf1_write16(gus, SNDRV_GF1_VW_VOLUME, vol);
 		pcmp->final_volume = 1;
-		spin_unlock_irqrestore(&gus->reg_lock, flags);
+		spin_unlock(&gus->reg_lock);
 	}
 	spin_unlock_irqrestore(&gus->voice_alloc, flags);
 	return change;
--
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