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SubjectRe: [PATCH 1/5] tracing: Prevent kernel oops with corrupted buffer
On Tue, Jan 26, 2010 at 02:32:23PM -0800, Andrew Morton wrote:
> > + if (WARN_ON_ONCE(pid < 0)) {
> > + strcpy(comm, "<XXX>");
> > + return;
> > + }
> > +
> > if (pid > PID_MAX_DEFAULT) {
> > strcpy(comm, "<...>");
> > return;
>
> But why is it WARN_ON_ONCE()? That will only fix the problem a single
> time. On the second occurrence, it will oops again.



The warning will be produced only once, but after that,
the condition is still checked like a simple if:

#define WARN_ON_ONCE(condition) ({ \
static bool __warned; \
int __ret_warn_once = !!(condition); \
\
if (unlikely(__ret_warn_once)) \
if (WARN_ON(!__warned)) \
__warned = true; \
unlikely(__ret_warn_once); \
})


And since this function can be called anytime we have a trace
to print to the user, we don't want to encumber with thousands
of warnings.



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