Messages in this thread | | | Subject | Re: [PATCH v5 01/45] percpu_rwlock: Introduce the global reader-writer lock backend | From | Steven Rostedt <> | Date | Tue, 22 Jan 2013 14:32:32 -0500 |
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On Tue, 2013-01-22 at 13:03 +0530, Srivatsa S. Bhat wrote: > A straight-forward (and obvious) algorithm to implement Per-CPU Reader-Writer > locks can also lead to too many deadlock possibilities which can make it very > hard/impossible to use. This is explained in the example below, which helps > justify the need for a different algorithm to implement flexible Per-CPU > Reader-Writer locks. > > We can use global rwlocks as shown below safely, without fear of deadlocks: > > Readers: > > CPU 0 CPU 1 > ------ ------ > > 1. spin_lock(&random_lock); read_lock(&my_rwlock); > > > 2. read_lock(&my_rwlock); spin_lock(&random_lock); > > > Writer: > > CPU 2: > ------ > > write_lock(&my_rwlock); >
I thought global locks are now fair. That is, a reader will block if a writer is waiting. Hence, the above should deadlock on the current rwlock_t types.
We need to fix those locations (or better yet, remove all rwlocks ;-)
-- Steve
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