Messages in this thread Patch in this message | | | Date | Wed, 2 Sep 2020 09:24:32 +0200 | From | peterz@infradea ... | Subject | Re: [PATCH v2 11/11] lockdep,trace: Expose tracepoints |
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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?
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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);
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