On Wed, 25 Mar 2015, Steven Rostedt wrote: > It has come to my attention that this_cpu_read/write are horrible on > architectures other than x86. Worse yet, they actually disable > preemption or interrupts! This caused some unexpected tracing results > on ARM. This isnt something new and I thought the comment was dropped from the patch? This is a plain error in using this_cpu_* where __this_cpu_* would have been sufficient. Code was uselessly disabling preemption twice. > Which is unacceptable for locations that know they are within preempt > disabled or interrupt disabled locations. Well yes. Thats why the __this_cpu ops are there to avoid this overhead. > I also changed the recursive_unlock() to use two local variables instead > of accessing the per_cpu variable twice. Ok gotta look at that. > static __always_inline void trace_recursive_unlock(void) > { > - unsigned int val = this_cpu_read(current_context); > + unsigned int val = __this_cpu_read(current_context); > > - val--; > - val &= this_cpu_read(current_context); > - this_cpu_write(current_context, val); > + val &= val & (val - 1); > + __this_cpu_write(current_context, val); > } Ummm... This is does not look like an equivalent thing. Should this not be: unsigned int val = __this_cpu_read(current_context); unsigned int newval = val - 1; newval &= val; __this_cpu_write(current_context, newval); or more compact unsigned int val = __this_cpu_read(current_context); __this_cpu_write(current_context, val & (val - 1)); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html