[alsa-devel] [patch 1/2] OSS: soundcard: locking bug in sound_ioctl()

Josh Triplett josh at joshtriplett.org
Tue Oct 12 08:43:26 CEST 2010

On Tue, Oct 12, 2010 at 08:39:14AM +0200, Arnd Bergmann wrote:
> On Tuesday 12 October 2010 00:23:08 Josh Triplett wrote:
> > Assuming that the underlying function only returns zero/non-zero and
> > that the actual return value doesn't matter, then you can use the
> > __cond_lock macro from compiler.h for this:
> > 
> > # define __cond_lock(x,c)       ((c) ? ({ __acquire(x); 1; }) : 0)
> > 
> The return from mutex_lock_{killable,interruptible} is an error
> value, not true/false, so it actually matters. We know that the only
> possible error that is currently returned is -EINTR though, so we
> could do a similar trick and define another
> #define __cond_mutex(x, c)	((!c) ? ({ __acquire(x); 0; }) : -EINTR)
> My fear was that this would impact code generation.

If __cond_lock doesn't fit, then you could just define a generic wrapper
to capture the pattern of preserving a function's return value, and use
that for all the mutex calls.  And if you just preserve the return
value, and __acquire compiles to nothing for GCC, then GCC should just
optimize away the extra copy into a local variable.

- Josh Triplett

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