Re: [alsa-devel] [patch 1/2] OSS: soundcard: locking bug in sound_ioctl()
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.
Arnd
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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Arnd Bergmann -
Josh Triplett