On 9/2/20 12:24 AM, pet...@infradead.org wrote: > On Tue, Sep 01, 2020 at 08:51:46PM -0700, Guenter Roeck wrote: >> On Fri, Aug 21, 2020 at 10:47:49AM +0200, Peter Zijlstra wrote: >>> The lockdep tracepoints are under the lockdep recursion counter, this >>> has a bunch of nasty side effects: >>> >>> - TRACE_IRQFLAGS doesn't work across the entire tracepoint >>> >>> - RCU-lockdep doesn't see the tracepoints either, hiding numerous >>> "suspicious RCU usage" warnings. >>> >>> Pull the trace_lock_*() tracepoints completely out from under the >>> lockdep recursion handling and completely rely on the trace level >>> recusion handling -- also, tracing *SHOULD* not be taking locks in any >>> case. >>> >> >> Wonder what is worse - the problem or its fix. This patch results in >> a number of WARNING backtraces for several archtectures/platforms. >> Reverting it fixes the problems. > > Without all this there was a recursion that could crash. But yes, > tedious. > > OTOH the warnings are about real bugs that were pre-existing, we now see > them and can fix them. > > I'll reply to ARM separately, but let's have a peek at s390. > >> s390: >> >> [ 19.490586] ============================= >> [ 19.490752] WARNING: suspicious RCU usage >> [ 19.490921] 5.9.0-rc3 #1 Not tainted >> [ 19.491086] ----------------------------- >> [ 19.491253] include/trace/events/lock.h:37 suspicious >> rcu_dereference_check() usage! > >> [ 19.493147] [<00000000001d5de2>] lock_acquire+0x41a/0x498 >> [ 19.493320] [<0000000000103b72>] enabled_wait+0xca/0x198 >> [ 19.493493] [<0000000000103f80>] arch_cpu_idle+0x20/0x38 > > Does this help? > > --- > > diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c > index c73f50649e7e..f7f1e64e0d98 100644 > --- a/arch/s390/kernel/idle.c > +++ b/arch/s390/kernel/idle.c > @@ -39,14 +39,13 @@ void enabled_wait(void) > local_irq_restore(flags); > > /* Account time spent with enabled wait psw loaded as idle time. */ > - /* XXX seqcount has tracepoints that require RCU */ > - write_seqcount_begin(&idle->seqcount); > + raw_write_seqcount_begin(&idle->seqcount); > idle_time = idle->clock_idle_exit - idle->clock_idle_enter; > idle->clock_idle_enter = idle->clock_idle_exit = 0ULL; > idle->idle_time += idle_time; > idle->idle_count++; > account_idle_time(cputime_to_nsecs(idle_time)); > - write_seqcount_end(&idle->seqcount); > + raw_write_seqcount_end(&idle->seqcount); > } > NOKPROBE_SYMBOL(enabled_wait); >
Yes, it does. Tested-by: Guenter Roeck <li...@roeck-us.net> Guenter
