On Mon, 3 Dec 2007, Jarek Poplawski wrote: > > System sleep start: > > down_read(notifier-chain rwsem); > > call the notifier routine > > down_write(&system_sleep_in_progress_rwsem); > > up_read(notifier-chain rwsem); > > > > System sleep end: > > down_read(notifier-chain rwsem); > > call the notifier routine > > up_write(&system_sleep_in_progress_rwsem); > > up_read(notifier-chain rwsem); > > > > This creates a lockdep violation; each rwsem in turn is locked while > > the other is being held. However the only way this could lead to > > deadlock would be if there was already a bug in the system Power > > Management code (overlapping notifications). > > Actually, IMHO, there is no reason for any lockdep violation: > > thread #1: has down_read(A); waits for #2 to down_write(B) > thread #2: has down_write(B); never waits for #1 to down_read(A) > > So, deadlock isn't possible here. If lockdep reports something else it > should be fixed (and you'd be right to omit lockdep until this is > done). I think the reasoning goes the way Arjan described. Suppose in between #1 and #2 there is thread #3 trying to do down_write(A) and waiting for #1. Then thread #2 doesn't have to wait for #1 directly, but it would have to wait for #3. In my case the simplest answer appears to be the replace the rwsem with something slightly more complicated (a mutex plus a boolean flag -- the loss of concurrency won't matter much since it isn't on a hot path). Thanks for the comment. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
