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Date: Tue, 6 Oct 2015 11:07:34 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Josh Triplett <josh@...htriplett.org> Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com Subject: Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() On Tue, Oct 06, 2015 at 10:43:11AM -0700, Josh Triplett wrote: > On Tue, Oct 06, 2015 at 10:36:46AM -0700, Paul E. McKenney wrote: > > On Tue, Oct 06, 2015 at 10:18:39AM -0700, Josh Triplett wrote: > > > On Tue, Oct 06, 2015 at 09:13:42AM -0700, Paul E. McKenney wrote: > > > > Currently, __srcu_read_lock() cannot be invoked from restricted > > > > environments because it contains calls to preempt_disable() and > > > > preempt_enable(), both of which can invoke lockdep, which is a bad > > > > idea in some restricted execution modes. This commit therefore moves > > > > the preempt_disable() and preempt_enable() from __srcu_read_lock() > > > > to srcu_read_lock(). It also inserts the preempt_disable() and > > > > preempt_enable() around the call to __srcu_read_lock() in do_exit(). > > > > > > What restricted environments do you intend to invoke > > > __srcu_read_lock from? > > > > > > This change seems fine, but I don't see any change in this patch series > > > that needs this, hence my curiosity. > > > > Someone asked me for it, and now I cannot find it. :-( > > > > Something to the effect of when running unmapped during exception entry > > or something like that. I guess one way to find out would be to remove > > the commit and see who complained, but on the other hand, it arguably > > makes more sense to have only the bare mechanism is __srcu_read_lock() > > and put the environmental protection into srcu_read_lock(). > > I agree; I just find the idea that someone would need to call > __srcu_read_lock rather than srcu_read_lock odd and worthy of further > understanding. :) And they did supply an explanation that seemed satisfactory at the time, but I cannot find that either. I clearly need to track that sort of stuff better! Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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