On Fri, 1 Dec 2023 15:17:35 +0100 Petr Pavlu <petr.pa...@suse.com> wrote:
> Ok, keeping the current approach, my plan for v2 is to prepare the > following patches: > > * Fix for the missing increment+decrement of trace_buffered_event_cnt > on the current CPU in trace_buffered_event_disable(). > > Replace smp_call_function_many() with on_each_cpu_mask() in > trace_buffered_event_disable(). The on_each_cpu_mask() function has > also an advantage that it itself disables preemption so doing that can > be then removed from trace_buffered_event_disable(). OK. > > * Fix the potential race between trace_buffered_event_enable() and > trace_event_buffer_lock_reserve() where the latter might already see > a valid trace_buffered_event pointer but not all initialization yet. > > I think this might be actually best to address by using the same > maintenance exclusion as is implemented in > trace_buffered_event_disable(). It would make both maintenance > operations consistent but for the cost of making the enable operation > somewhat slower. I wouldn't do them the same just to make them consistent. I think the smp_wmb() is sufficient. Don't you think? > > * Fix the WARN_ON_ONCE(!trace_buffered_event_ref) issued in > trace_buffered_event_disable() when trace_buffered_event_enable() > previously fails. > > Add a variable/flag tracking whether trace_buffered_event is currently > allocated and use that for driving if a new allocation needs to be > done when trace_buffered_event_enable() is called, or the buffers > should be really freed when trace_buffered_event_disable() is invoked. > > Not sure if the mentioned alternative of leaving trace_buffered_event > partially initialized on failure is preferred instead. I do not really have a preference for either solution. They both are bad if it happens ;-) > > * Fix the potential race between trace_buffered_event_disable() and > trace_event_buffer_lock_reserve() where the latter might still grab > a pointer from trace_buffered_event that is being freed. > > Replace smp_wmb() with synchronize_rcu() in > trace_buffered_event_disable(). Sounds good. Thanks! -- Steve
