Messages in this thread | | | Date | Tue, 31 Jan 2006 12:21:54 +0100 | From | Ingo Molnar <> | Subject | Re: [lock validator] inet6_destroy_sock(): soft-safe -> soft-unsafe lock dependency |
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* David S. Miller <davem@davemloft.net> wrote:
> From: Herbert Xu <herbert@gondor.apana.org.au> > Date: Tue, 31 Jan 2006 21:27:58 +1100 > > > tcp_close is only called from process context. The rule for sk_dst_lock > > is that it must also only be obtained in process context. On the other > > hand, it is true that sk_lock can be obtained in softirq context. > > > > In this particular case, sk_dst_lock is obtained by tcp_close with > > softirqs disabled. This is not a problem in itself since we're not > > trying to get sk_dst_lock from a real softirq context (as opposed to > > process context with softirq disabled). > > > > I believe this warning comes about because the validator creates a > > dependency between sk_lock and sk_dst_lock. It then infers from this > > dependency that in softirq contexts where sk_lock is obtained the code > > may also attempt to obtain sk_dst_lock. > > > > This inference is where the validator errs. sk_dst_lock is never > > (or should never be, and as far as I can see none of the traces show > > it to do so) obtained in a real softirq context. > > Herbert's analysis is correct. This unique locking strategy is used > by tcp_close() because at this point it knows that every single > reference to this socket in the system is gone once it takes the > socket lock with BH disabled. > > And that known invariant is why this is correct, and the locking > validator has no way to figure this out.
ok, thanks for the analysis! I'll fix this with an explicit hint to the validator.
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