On Tue, 2006-07-04 at 11:15 +0200, Duncan Sands wrote:
> Linux version 2.6.17-git22 (duncan@baldrick) (gcc version 4.0.3 (Ubuntu 4.0.3-1ubuntu5)) #20 PREEMPT Tue Jul 4 10:35:04 CEST 2006
>
>
> [ 612.924372] =========================================================
> [ 612.948112] [ INFO: possible irq lock inversion dependency detected ]
> [ 612.967383] ---------------------------------------------------------
> [ 612.986657] aplay/5128 just changed the state of lock:
> [ 613.002034] (&ins->scbs[index].lock){-...}, at: [<e099f95e>] cs46xx_dsp_remove_scb+0x1e/0xca [snd_cs46xx]
> [ 613.031150] but this lock was taken by another, hard-irq-safe lock in the past:
> [ 613.053019] (&substream->self_group.lock){+...}
> [ 613.066369]
> [ 613.066371] and interrupts could create inverse lock ordering between them.
> [ 613.066374]
ok so there is a code sequence where the locking is
substream->self_group.lock -> ins->scbs[index].lock
substream->self_group.lock is interrupt safe, and taken from irq context
as well (trace is snipped for brevity)
so what can happen is
cpu 0 cpu 1
user context user context
take ins->scbs[index].lock without disabling interrupts
get substream->self_group.lock (irqsafe)
try to get ins->scbs[index].lock (spins)
interrupt happens
try to get substream->self_group.lock (spins)
which is an obvious AB-BA deadlock
fix is to just take the lock with _irqsafe
Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
---
sound/pci/cs46xx/dsp_spos_scb_lib.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
Index: linux-2.6.17-mm4/sound/pci/cs46xx/dsp_spos_scb_lib.c
===================================================================
--- linux-2.6.17-mm4.orig/sound/pci/cs46xx/dsp_spos_scb_lib.c
+++ linux-2.6.17-mm4/sound/pci/cs46xx/dsp_spos_scb_lib.c
@@ -180,6 +180,7 @@ static void _dsp_clear_sample_buffer (st
void cs46xx_dsp_remove_scb (struct snd_cs46xx *chip, struct dsp_scb_descriptor * scb)
{
struct dsp_spos_instance * ins = chip->dsp_spos_instance;
+ unsignded long flags;
/* check integrety */
snd_assert ( (scb->index >= 0 &&
@@ -194,9 +195,9 @@ void cs46xx_dsp_remove_scb (struct snd_c
goto _end);
#endif
- spin_lock(&scb->lock);
+ spin_lock_irqsave(&scb->lock, flags);
_dsp_unlink_scb (chip,scb);
- spin_unlock(&scb->lock);
+ spin_unlock_irqrestore(&scb->lock, flags);
cs46xx_dsp_proc_free_scb_desc(scb);
snd_assert (scb->scb_symbol != NULL, return );
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