> -----Original Message----- > From: Peter Zijlstra [mailto:peterz@xxxxxxxxxxxxx] > Sent: Friday, May 19, 2017 7:30 PM > To: Byungchul Park > Cc: mingo@xxxxxxxxxx; tglx@xxxxxxxxxxxxx; walken@xxxxxxxxxx; > boqun.feng@xxxxxxxxx; kirill@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > linux-mm@xxxxxxxxx; iamjoonsoo.kim@xxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; > willy@xxxxxxxxxxxxx; npiggin@xxxxxxxxx; kernel-team@xxxxxxx > Subject: Re: [PATCH v6 05/15] lockdep: Implement crossrelease feature > > 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). Got it. Thank you. > You're asking this in relation to the rollback thing, right? I think we Exactly. I wanted to make it clear when implementing the rollback for irqs and works of workqueue. > should only save the state when hardirq_context goes from 0->1 and > restore on 1->0. Yes, it's already done in v6, as you are saying. Thank you very much. -- 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>
