Messages in this thread | | | Date | Wed, 14 Sep 2011 05:40:13 +0100 | From | Al Viro <> | Subject | Re: Lockdep and rw_semaphores |
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On Tue, Sep 13, 2011 at 09:55:25PM -0400, Vladislav Bolkhovitin wrote:
> > thread 1: > > down_read(&A); /* got it */ > > thread 2: > > down_read(&B); /* got it */ > > thread 3: > > down_write(&A); /* blocked until thread 1 releases A */
That's the only thread here doing down_write() on A
> > thread 4: > > down_write(&B); /* blocked until thread 2 releases B */
... and that's the only thread here doing down_write() on B. And neither of those is holding any other locks. No nesting.
> 1. Reverse read locking isn't always a deadlock. For instance, if only 1 write > thread participating and doesn't do nested write locking, which is a quite valid > scenario, because by design of rw locks they are used with many readers and > limited amount of rare writers.
Um? If you mean that here we have two threads doing down_write(), remember that you've got two locks.
> So, it should be better if this warning is issued, if there is >1 thread write > locking detected on any participated rw lock, and illustrated with a correct > explanation.
Which would be which threads, in the situation described above? Again, we have no nesting for writes and we have one thread attempting down_write() for any given lock. Two locks, two writers in total...
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