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Date: Thu, 12 Jul 2018 01:38:05 -0700 From: Joel Fernandes <joel@...lfernandes.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>, Byungchul Park <byungchul.park@....com>, Ingo Molnar <mingo@...hat.com>, Julia Cartwright <julia@...com>, linux-kselftest@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Namhyung Kim <namhyung@...nel.org>, Paul McKenney <paulmck@...ux.vnet.ibm.com>, Thomas Glexiner <tglx@...utronix.de>, Tom Zanussi <tom.zanussi@...ux.intel.com>, kernel-team@...roid.com Subject: Re: [PATCH v9 5/7] tracing: Centralize preemptirq tracepoints and unify their usage On Wed, Jul 11, 2018 at 09:19:44AM -0400, Steven Rostedt wrote: > > > protection to prevent something like the following case: a spin_lock is > > > taken. Then lockdep_acquired is called. That does a raw_local_irq_save > > > and then sets lockdep_recursion, and then calls __lockdep_acquired. In > > > this function, a call to get_lock_stats happens which calls > > > preempt_disable, which calls trace IRQS off somewhere which enters my > > > tracepoint code and sets the tracing_irq_cpu flag to prevent recursion. > > > This flag is then never cleared causing lockdep paths to never be > > > entered and thus causing splats and other bad things. > > > > Would it not be much easier to avoid that entirely, afaict all > > get/put_lock_stats() callers already have IRQs disabled, so that > > (traced) preempt fiddling is entirely superfluous. > > Agreed. Looks like a good clean up. So actually with or without the clean up, I don't see any issues with dropping lockdep_recursing in my tests at the moment. I'm not sure something else changed between then and now causing the issue to go away. I can include Peter's clean up in my series though if he's Ok with it since you guys agree its a good clean up anyway. Would you prefer I did that, and then also dropped the lockdep_recursing checks? Or should I keep the lockdep_recursing() checks just to be safe? Do you see cases where you want irqsoff tracing while lockdep_recursing() is true? thanks, - Joel
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