On Fri, 11 Oct 2024 10:05:51 +0200 Petr Pavlu <petr.pa...@suse.com> wrote:
> On 10/11/24 01:58, Steven Rostedt wrote: > > From: Steven Rostedt <rost...@goodmis.org> > > > > In order to prevent any subtle races with the buffer update counter, > > change it to an atomic_t. Also, since atomic_t is 32 bits, move its > > location in the ring_buffer_per_cpu structure next to "current_context" as > > that too is only 32 bits (making 64 bit alignment). > > > > The counter is only used to detect that the buffer has been updated when > > the buffer verifier check is being done. It's not really that important > > that it's atomic or not. But since the updates to the counter are never in > > the fast path, having it be consistent isn't a bad thing. > > > > Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org> > > --- > > Note, this is based on top of: > > > > > > https://lore.kernel.org/linux-trace-kernel/20240715145141.5528-1-petr.pa...@suse.com/ > > > > Sorry for not replying to your last comment on my patch, I was ill. > > The member ring_buffer_per_cpu.cnt is intended to be accessed under the > reader_lock, same as the pages pointer which it is tied to, so this > change shouldn't be strictly needed. > Right, but there was one location that the cnt was updated outside the lock. The one I commented on. But instead of adding a lock around it, I decided to just make it an atomic. Then there would be no need for the lock. Hmm, it still needs a memory barrier though. At least a smp_mb__after_atomic(). -- Steve
