On Wed, 25 Jun 2025 18:56:06 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> static __always_inline void unwind_reset_info(void)
> {
> - if (unlikely(current->unwind_info.cache))
> + /* Exit out early if this was never used */
> + if (likely(!current->unwind_info.timestamp))
> + return;
I found that this breaks the use of perf using the unwind_user_faultable()
directly and not relying on the deferred infrastructure (which it does when
it traces a single task and also needs to remove the separate in_nmi()
code). Because this still requires the nr_entries to be set to zero.
The clearing of the nr_entries has to be separate from the timestamp. To
prevent unneeded writes after the cache is allocated, should we check the
nr_entries is set before writing zero?
if (current->unwind_info.cache && current->unwind_info.cache->nr_entries)
current->unwind_info.cache->nr_entries = 0;
?
-- Steve
> +
> + if (current->unwind_info.cache)
> current->unwind_info.cache->nr_entries = 0;
> + current->unwind_info.timestamp = 0;
> }
