Messages in this thread | | | Date | Tue, 3 Nov 2015 07:15:38 -0800 | From | "Paul E. McKenney" <> | Subject | Re: Can srcu_read_lock() be called from interrupt context? |
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On Tue, Nov 03, 2015 at 03:47:17PM +0100, Peter Zijlstra wrote: > On Tue, Nov 03, 2015 at 01:55:39AM -0800, Paul E. McKenney wrote: > > On Mon, Nov 02, 2015 at 05:56:56PM -0800, Yunhong Jiang wrote: > > > Hi, Paul > > > I have a question to the srcu_read_lock(). Can it be invoked on > > > interrupt context? According to > > > http://lxr.free-electrons.com/source/kernel/rcu/srcu.c#L292 it can only be > > > called from process context, but according to > > > http://lxr.free-electrons.com/source/include/linux/srcu.h#L213 seems it's ok > > > from irq context only if it matches with the srcu_read_unlock. Can you > > > please give some hints? > > > > Adding Lai Jianshan for his thoughts. > > > > I believe that srcu.h is correct, at least assuming that interrupts do > > not nest too deeply. (If they were to nest four billion deep, then the > > ->seq[] counter could overflow, defeating the checks, but the CPU stack > > would have overflowed long before.) > > It seems like a strange constraint to me; not being able to use > srcu_read_lock() from IRQ (or even NMI) context. And looking at the > various implementations of it nothing ever prohibited this. > > While srcu _allows_ for sleeping while holding the read side primitives, > it is not required at all. > > So I would suggest amending the comment and RCU/checklist.txt.
We need to hear from Lai. I -think- that it is OK for one srcu_read_lock() to interrupt another, but I could easily be missing something.
> Even call_srcu() should be IRQ-safe.
Looks plausible to me. Lai?
Thanx, Paul
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