* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > I came up with the below hackery, seems to actually boot and such > on a lockdep enabled kernel (although Ingo did report lockups with > a partial version of the patch, still need to look at that). > > The idea is to use the console_sem.lock instead of the semaphore > itself, we flush the console when console_sem.count > 0, which > means its uncontended. Its more or less equivalent to > down_trylock() + up(), except it never releases the sem internal > lock, and optimizes the count fiddling away. > > It doesn't require a wakeup because any real semaphore contention > will still be spinning on the spinlock instead of enqueueing itself > on the waitlist. > > Its rather ugly, exposes semaphore internals in places it > shouldn't, although we could of course expose some primitives for > this, but then people might thing it'd be okay to use them etc.. > > /me puts on the asbestos underwear Hm, the no-wakeup aspect seems rather useful. Could we perhaps remove console_sem and replace it with a mutex and do something like this with a mutex and its ->wait_lock? We'd have two happy side effects: - we'd thus remove one of the last core kernel semaphore users - we'd gain lockdep coverage for console locking as a bonus ... Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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