Messages in this thread | | | Date | Tue, 25 Aug 2015 13:56:27 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] cred: Remove unnecessary kdebug atomic reads |
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On Tue, 25 Aug 2015 13:51:06 -0700 Joe Perches <joe@perches.com> wrote:
> On Tue, 2015-08-25 at 13:39 -0700, Andrew Morton wrote: > > On Tue, 25 Aug 2015 09:53:51 -0700 Joe Perches <joe@perches.com> wrote: > > > commit e0e817392b9a ("CRED: Add some configurable debugging [try #6]") > > > added the kdebug mechanism to this file back in 2009. > > > > > > The kdebug macro calls no_printk which always evaluates arguments. > > > > > > Most of the kdebug uses have an unnecessary call of > > > atomic_read(&cred->usage) > > > > > > Make the kdebug macro do nothing by defining it with > > > do { if (0) no_printk(...); } while (0) > > > when not enabled. > [] > > Did you consider doing this within no_printk()? > > Yes. > > > That would break code > > which is relying on side-effects in the evaluation of a printk arg but > > that's pretty weird and I bet there isn't (and won't be) such code. > > I'll bet you there is more than a little and I don't want to > experiment with it unconditionally. > > All printks would need to be evaluated for that side-effect. > > Safer would be to create a new no_eval_printk macro and convert > the no_printk uses over to that as appropriate and possibly create > a CONFIG_ option to use no_eval_printk instead of no_printk/printk > and let the adventurous find the side-effects. > > Maybe a coccinelle script can be written to find all the locations > with evaluated non-constant expression arguments with side-effects.
wimp.
That duplicated printk in cred.c is nasty. We could do this?
#if 0 #define __kdebug printk #else #define __kdebug if (0) no_printk #endif
#define kdebug(FMT, ...) \ __kdebug(...)
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