On Fri, 21 Aug 2020 at 14:31, Marco Elver <el...@google.com> wrote: > In the core runtime, we must minimize any calls to external library > functions to avoid any kind of recursion. This can happen even though > instrumentation is disabled for called functions, but tracing is > enabled. > > Most recently, prandom_u32() added a tracepoint, which can cause > problems for KCSAN even if the rcuidle variant is used. For example: > kcsan -> prandom_u32() -> trace_prandom_u32_rcuidle -> > srcu_read_lock_notrace -> __srcu_read_lock -> kcsan ... > > While we could disable KCSAN in kcsan_setup_watchpoint(), this does not > solve other unexpected behaviour we may get due recursing into functions > that may not be tolerant to such recursion: > __srcu_read_lock -> kcsan -> ... -> __srcu_read_lock > > Therefore, switch to using prandom_u32_state(), which is uninstrumented, > and does not have a tracepoint. > > Link: https://lkml.kernel.org/r/20200821063043.1949509-1-el...@google.com > Link: https://lkml.kernel.org/r/20200820172046.ga177...@elver.google.com > Signed-off-by: Marco Elver <el...@google.com> > --- > Applies to latest -rcu/dev only. > > Let's wait a bit to see what happens with > https://lkml.kernel.org/r/20200821063043.1949509-1-el...@google.com, > just in case there's a better solution that might make this patch redundant.
Paul, feel free to pick this up. I wanted to wait until after plumbers to see what happens, but maybe it's better to give the heads-up now, so this is in time for the next pull-request. It seems that prandom_u32() will keep its tracepoint, which means we definitely need this to make KCSAN compatible with tracing again. Thanks, -- Marco
