On Tue, Oct 27, 2020 at 03:31:41PM -0400, Qian Cai wrote: > On Mon, 2020-10-12 at 11:11 +0800, Boqun Feng wrote: > > Hi, > > > > On Fri, Oct 09, 2020 at 09:41:24AM -0400, Qian Cai wrote: > > > On Fri, 2020-10-09 at 07:58 +0000, tip-bot2 for Peter Zijlstra wrote: > > > > The following commit has been merged into the locking/core branch of tip: > > > > > > > > Commit-ID: 4d004099a668c41522242aa146a38cc4eb59cb1e > > > > Gitweb: > > > > https://git.kernel.org/tip/4d004099a668c41522242aa146a38cc4eb59cb1e > > > > Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > > > AuthorDate: Fri, 02 Oct 2020 11:04:21 +02:00 > > > > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > > > > CommitterDate: Fri, 09 Oct 2020 08:53:30 +02:00 > > > > > > > > lockdep: Fix lockdep recursion > > > > > > > > Steve reported that lockdep_assert*irq*(), when nested inside lockdep > > > > itself, will trigger a false-positive. > > > > > > > > One example is the stack-trace code, as called from inside lockdep, > > > > triggering tracing, which in turn calls RCU, which then uses > > > > lockdep_assert_irqs_disabled(). > > > > > > > > Fixes: a21ee6055c30 ("lockdep: Change hardirq{s_enabled,_context} to per- > > > > cpu > > > > variables") > > > > Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx> > > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > > > > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> > > > > > > Reverting this linux-next commit fixed booting RCU-list warnings everywhere. > > > > > > > I think this happened because in this commit debug_lockdep_rcu_enabled() > > didn't adopt to the change that made lockdep_recursion a percpu > > variable? > > > > Qian, mind to try the following? > > Boqun, Paul, may I ask what's the latest with the fixes? I must admit that I got > lost in this thread, but I remember that the patch from Boqun below at least > silence quite some of those warnings if not all. The problem is that some of > those warnings would trigger a lockdep circular locks warning due to printk() > with some locks held which in turn disabling the lockdep, makes our test runs > inefficient. If I have the right email thread associated with the right fixes, these commits in -rcu should be what you are looking for: 73b658b6b7d5 ("rcu: Prevent lockdep-RCU splats on lock acquisition/release") 626b79aa935a ("x86/smpboot: Move rcu_cpu_starting() earlier") And maybe this one as well: 3a6f638cb95b ("rcu,ftrace: Fix ftrace recursion") Please let me know if these commits do not fix things. Thanx, Paul > > Although, arguably the problem still exists, i.e. we still have an RCU > > read-side critical section inside lock_acquire(), which may be called on > > a yet-to-online CPU, which RCU doesn't watch. I think this used to be OK > > because we don't "free" anything from lockdep, IOW, there is no > > synchronize_rcu() or call_rcu() that _needs_ to wait for the RCU > > read-side critical sections inside lockdep. But now we lock class > > recycling, so it might be a problem. > > > > That said, currently validate_chain() and lock class recycling are > > mutually excluded via graph_lock, so we are safe for this one ;-) > > > > ----------->8 > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > > index 39334d2d2b37..35d9bab65b75 100644 > > --- a/kernel/rcu/update.c > > +++ b/kernel/rcu/update.c > > @@ -275,8 +275,8 @@ EXPORT_SYMBOL_GPL(rcu_callback_map); > > > > noinstr int notrace debug_lockdep_rcu_enabled(void) > > { > > - return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks && > > - current->lockdep_recursion == 0; > > + return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && > > + __lockdep_enabled; > > } > > EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); > >
