From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4E1B5638.1050005@domain.hid> Date: Mon, 11 Jul 2011 21:59:52 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <4E1B469A.8000703@domain.hid> <4E1B4AC0.80506@domain.hid> <4E1B4C19.2070205@domain.hid> <4E1B542B.2010906@domain.hid> In-Reply-To: <4E1B542B.2010906@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigD75DF8A921E67B9985089580" Sender: jan.kiszka@domain.hid Subject: Re: [Xenomai-core] [Xenomai-git] Jan Kiszka : nucleus: Fix race between gatekeeper and thread deletion List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: Xenomai core This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigD75DF8A921E67B9985089580 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 2011-07-11 21:51, Gilles Chanteperdrix wrote: > On 07/11/2011 09:16 PM, Jan Kiszka wrote: >> On 2011-07-11 21:10, Jan Kiszka wrote: >>> On 2011-07-11 20:53, Gilles Chanteperdrix wrote: >>>> On 07/08/2011 06:29 PM, GIT version control wrote: >>>>> @@ -2528,6 +2534,22 @@ static inline void do_taskexit_event(struct = task_struct *p) >>>>> magic =3D xnthread_get_magic(thread); >>>>> =20 >>>>> xnlock_get_irqsave(&nklock, s); >>>>> + >>>>> + gksched =3D thread->gksched; >>>>> + if (gksched) { >>>>> + xnlock_put_irqrestore(&nklock, s); >>>> >>>> Are we sure irqs are on here? Are you sure that what is needed is no= t an >>>> xnlock_clear_irqon? >>> >>> We are in the context of do_exit. Not only IRQs are on, also preempti= on. >>> And surely no nklock is held. >>> >>>> Furthermore, I do not understand how we >>>> "synchronize" with the gatekeeper, how is the gatekeeper garanteed t= o >>>> wait for this assignment? >>> >>> The gatekeeper holds the gksync token while it's active. We request i= t, >>> thus we wait for the gatekeeper to become idle again. While it is idl= e, >>> we reset the queued reference - but I just realized that this may tra= mp >>> on other tasks' values. I need to add a check that the value to be >>> null'ified is actually still ours. >> >> Thinking again, that's actually not a problem: gktarget is only needed= >> while gksync is zero - but then we won't get hold of it anyway and, >> thus, can't cause any damage. >=20 > Well, you make it look like it does not work. From what I understand, > what you want is to set gktarget to null if a task being hardened is > destroyed. But by waiting for the semaphore, you actually wait for the > harden to be complete, so setting to NULL is useless. Or am I missing > something else? Setting to NULL is probably unneeded but still better than rely on the gatekeeper never waking up spuriously and then dereferencing a stale pointer. The key element of this fix is waitng on gksync, thus on the completion of the non-RT part of the hardening. Actually, this part usually fails as the target task received a termination signal at this point. Jan --------------enigD75DF8A921E67B9985089580 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk4bVjgACgkQitSsb3rl5xSKmQCg0kxBt4ciX9xovUdIfmhQRmBW tQMAmgJWx+HotTX442XiPpzLEZa7sVrW =V/Ae -----END PGP SIGNATURE----- --------------enigD75DF8A921E67B9985089580--