Re: [PATCH v2 1/1] Fix int1 recursion when no perf_bp_event is registeredy

[Jeff Merkey]

One thing I noticed in this section of code:

	/* Handle all the breakpoints that were triggered */
	for (i = 0; i < HBP_NUM; ++i) {
		if (likely(!(dr6 & (DR_TRAP0 << i))))
			continue;

                ... snip ...

		if (bp->hw.info.type == X86_BREAKPOINT_EXECUTE)
			args->regs->flags |= X86_EFLAGS_RF;

		rcu_read_unlock();
	}

Whoever wrote this loop did not seem to understand have observed the
code path in action on intel hardware.  There is NEVER a case I have
seen when the hardware sends multiple breakpoint statuses through dr6,
they are sent one at a time.  So the rolling check through all the
status bits is pointless since only one breakpoint will be reported by
the hardware at a time.  This is not to say that someone in the future
might may change it, but these interrupts are delivered one by one in
order and if there are duplicates (like a read/write breakpoint set at
the same address as an execute breakpoint.

Does anyone know why it was coded this way because its flat wrong.

Jeff
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/