Messages in this thread | | | Date | Sat, 08 Dec 2012 00:03:16 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [RFC PATCH v3 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context |
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On 12/07/2012 11:46 PM, Tejun Heo wrote: > Hello, again. > > On Fri, Dec 07, 2012 at 09:57:24AM -0800, Tejun Heo wrote: >> possible. Also, I think the right approach would be auditing each >> get_online_cpus_atomic() callsites and figure out proper locking order >> rather than implementing a construct this unusual especially as >> hunting down the incorrect cases shouldn't be difficult given proper >> lockdep annotation. > > On the second look, it looks like you're implementing proper > percpu_rwlock semantics
Ah, nice! I didn't realize that I was actually doing what I intended to avoid! ;-)
Looking at the implementation of lglocks, and going by Oleg's earlier comment that we just need to replace spinlock_t with rwlock_t in them to get percpu_rwlocks, I was horrified at the kinds of circular locking dependencies that they would be prone to, unless used carefully.
So I devised this scheme to be safe, while still having relaxed rules. But if *this* is what percpu_rwlocks should ideally look like, then great! :-)
> as readers aren't supposed to induce circular > dependency directly.
Yep, in this scheme, nobody will end up in circular dependency.
> Can you please work with Oleg to implement > proper percpu-rwlock and use that for CPU hotplug rather than > implementing it inside CPU hotplug? >
Sure, I'd be more than happy to!
Regards, Srivatsa S. Bhat
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