Re: [PATCH 1/1] exec: do not sleep in TASK_TRACED under ->cred_guard_mutex

From: David Howells
Date: Fri Sep 04 2009 - 04:45:37 EST

Roland McGrath <roland@xxxxxxxxxx> wrote:

> I certainly think it's right to hold the mutex only as long as necessary.
> Clearly holding it when we stop is wrong.

As far as I can tell, we don't hold it when we stop for debugging, or stop on

> I'm a bit concerned about holding it for arbitrary periods while we block
> in the filesystem code. e.g., consider the scenario with a hangs-forever
> NFS server or suchlike. But I'm not sure there is a reasonable way around
> that one.

If you drop the sem before committing the creds, you have to recalculate the
new credentials.

> The paired calls that leave the mutex locked in between should have some
> clear comments calling attention to their pairing. Aside from that making
> sure that subtlety is clear, I don't see any problems in the patch off hand.
> But I haven't scoured the code path lately to have full confidence.
> I'd like to hear David's reactions.

Looking at the patch description, I don't see how the patch it relevant to the
problem. There must be something else, either a call that's now being
skipped, or it's a matter of timing.

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