Re: 2.5.50: sleeping function called from illegal context

[Duncan Sands <baldrick@wanadoo.fr>]

On Tuesday 03 December 2002 13:01, Takashi Iwai wrote:
> At Tue, 3 Dec 2002 04:07:52 +0100,
>
> Duncan Sands wrote:
> > Got this with today 2.5 BK tree:
> >
> > Debug: sleeping function called from illegal context at
> > include/asm/semaphore.h:119 Call Trace:
> >  [<c0113f1a>] __might_sleep+0x52/0x58
> >  [<c024291a>] snd_cs46xx_iec958_put+0x36/0xf8
> >  [<c0217f28>] snd_ctl_elem_write+0xe0/0x1a4
> >  [<c0218360>] snd_ctl_ioctl+0x184/0x2c8
> >  [<c01462e6>] sys_ioctl+0x1fa/0x244
> >  [<c01088f7>] syscall_call+0x7/0xb
>
> ouch, we are using rwlock in the control ioctls.
>
> mutex is necessary for many controls, so we cannot suppress the use of
> mutex in control callbacks.
> but temporary unlocking looks ad-hoc, too...

If I understand right, the problem is that snd_ctl_elem_write
acquires control_rwlock, which is a rw spinlock.  It then calls
snd_cs46xx_iec958_put which acquires chip->spos_mutex,
which is a semaphore.  Thus the message.  Now I deduce
from the fact that  you don't use read_lock_irqsave that the
data structure is not read from interrupt context.  That means
you are only protecting against other CPUs.  So why not use
a semaphore instead of a spinlock?

All the best,

Duncan.


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