linux-kernel - Re: [PATCH 1/4] fanotify: flush outstanding perm requests on group destroy

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Date:	Tue, 24 Aug 2010 09:49:45 +0100
From:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
To:	Andreas Gruenbacher <agruen@...e.de>
CC:	Eric Paris <eparis@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] fanotify: flush outstanding perm requests on group destroy

On Tuesday 24 Aug 2010 02:13:11 Andreas Gruenbacher wrote:
> On Monday 23 August 2010 02:37:07 Eric Paris wrote:
> > When an fanotify listener is closing it may cause a deadlock between the
> > listener and the original task doing an fs operation.  If the original
> > task is waiting for a permissions response it will be holding the srcu
> > lock. The listener cannot clean up and exit until after that srcu lock
> > is syncronized. Thus deadlock.  The fix introduced here is to stop
> > accepting new permissions events when a listener is shutting down and to
> > grant permission for all outstanding events.  Thus the original task
> > will eventually release the srcu lock and the listener can complete
> > shutdown.
>
> This seems to work now.
>
> The one remaining issue is that processes blocked on perm events cannot be
> killed even with SIGKILL.  I don't know how hard it will be to fix this.

I think just switching to interruptible sleep in
fanotify_get_response_from_access should be fine. And it should probably deny
the current event when signal is received.

Tvrtko

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