On Fri, May 19, 2017 at 05:07:08PM +0900, Byungchul Park wrote: > On Tue, Mar 14, 2017 at 05:18:52PM +0900, Byungchul Park wrote: > > Lockdep is a runtime locking correctness validator that detects and > > reports a deadlock or its possibility by checking dependencies between > > locks. It's useful since it does not report just an actual deadlock but > > also the possibility of a deadlock that has not actually happened yet. > > That enables problems to be fixed before they affect real systems. > > > > However, this facility is only applicable to typical locks, such as > > spinlocks and mutexes, which are normally released within the context in > > which they were acquired. However, synchronization primitives like page > > locks or completions, which are allowed to be released in any context, > > also create dependencies and can cause a deadlock. So lockdep should > > track these locks to do a better job. The 'crossrelease' implementation > > makes these primitives also be tracked. > > Excuse me but I have a question... > > Only for maskable irq, can I assume that hardirq are prevented within > hardirq context? I remember that nested interrupts were allowed in the > past but not recommanded. But what about now? I'm curious about the > overall direction of kernel and current status. It would be very > appriciated if you answer it. So you're right. In general enabling IRQs from hardirq context is discouraged but allowed. However, if you were to do that with a lock held that would instantly make lockdep report a deadlock, as the lock is then both used from IRQ context and has IRQs enabled. So from a locking perspective you can assume no nesting, but from a state tracking pov we have to deal with the nesting I think (although it is very rare). You're asking this in relation to the rollback thing, right? I think we should only save the state when hardirq_context goes from 0->1 and restore on 1->0. If you're asking this for another reason, please clarify. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
