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. Even call_srcu() should be IRQ-safe. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
