Re: bug in tty ldisc and friends

From: Ingo Molnar
Date: Tue Jun 16 2009 - 06:46:25 EST

* Joerg Roedel <joerg.roedel@xxxxxxx> wrote:

> On Tue, Jun 16, 2009 at 12:29:10PM +0200, Ingo Molnar wrote:
> > We are now well below the limit for stack-trace entries.
> >
> > This is something we noticed recently: dma-debug uses a lot of
> > lock classes and thus creates a really large lock-graph,
> > depleting the reserves quickly.
> Is this considered a problem? I increased the hash-size to 1024
> for performance reasons (== 1024 spin_locks). But if it hurts to
> much in other places this can be reverted.

Lockdep running out of stack slots is a problem - but we dont want
to revert your patch: lockdep is really a helper to development, it
just observes, never hinders changes like that.

The good news is that the (untested) patch i sent should largely
solve this problem and reduce dma-debug's lockdep footprint by a
factor of 1024.

Reverting your change would only be a workaround really.

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