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SubjectRe: [PATCH 08/16] dma-debug: add core checking functions
On Sun, Jan 11, 2009 at 08:57:52AM +0100, Joerg Roedel wrote:
> On Sun, Jan 11, 2009 at 12:11:27AM +0100, Ingo Molnar wrote:
> >
> > * Joerg Roedel <joerg.roedel@amd.com> wrote:
> >
> > > +#define err_printk(dev, format, arg...) do { \
> > > + error_count += 1; \
> > > + if (show_all_errors || show_num_errors > 0) { \
> > > + WARN(1, "%s %s: " format, \
> > > + dev_driver_string(dev), \
> > > + dev_name(dev) , ## arg); \
> > > + } \
> > > + if (!show_all_errors && show_num_errors > 0) \
> > > + show_num_errors -= 1; \
> >
> > Note that the arithmetics here is SMP-unsafe: we only hold the hash bucket
> > so if two errors hit at once on two CPUs then the error tracking variables
> > can be accessed at once.
> >
> > I'd suggest a simple global lock for this error case (taken inside the
> > hash bucket lock), to be on the safe side.
> >
> > Also, please dont use a macro for this - printk details can be passed in
> > to helper inlines/functions too.
>
> Yeah, this is not SMP-safe, I know. But debugfs does not support
> atomic_t so I made the variables u32. But at least a race condition has
> not a too bad impact. What may habben is that error_count misses a error
> or the show_num_errors become negative.
> But if we really want to avoid this I think its better to add atomic_t
> support to debugfs. What do you think?

Even a global lock will not really help here because show_num_errors and
show_all_errors can be set using debugfs. Either we live with the small
race (with limited impact) or I add atomic_t support to debugfs.

Joerg



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