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Wed, 8 Apr 2020 18:41:59 +0000 (GMT) Received: from b03ledav004.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 463CF78066; Wed, 8 Apr 2020 18:41:49 +0000 (GMT) Received: from LeoBras (unknown [9.85.164.111]) by b03ledav004.gho.boulder.ibm.com (Postfix) with ESMTP; Wed, 8 Apr 2020 18:41:48 +0000 (GMT) Message-ID: <1452b1d770bd6c516606e4855f348773d1fa6e59.camel@linux.ibm.com> Subject: Re: [PATCH 1/1] powerpc/crash: Use NMI context for printk after crashing other CPUs From: Leonardo Bras To: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Greg Kroah-Hartman , Enrico Weigelt , Thomas Gleixner , Allison Randal , Christophe Leroy , Nicholas Piggin Date: Wed, 08 Apr 2020 15:41:37 -0300 In-Reply-To: <87y2r6jhuc.fsf@mpe.ellerman.id.au> References: <20200406174058.686436-1-leonardo@linux.ibm.com> <87y2r6jhuc.fsf@mpe.ellerman.id.au> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-lPjFWmObu0CMRxkrP/CR" User-Agent: Evolution 3.34.4 (3.34.4-1.fc31) MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.676 definitions=2020-04-07_10:2020-04-07, 2020-04-07 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 bulkscore=0 mlxlogscore=999 adultscore=0 priorityscore=1501 clxscore=1015 malwarescore=0 impostorscore=0 mlxscore=0 lowpriorityscore=0 suspectscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004080134 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" --=-lPjFWmObu0CMRxkrP/CR Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2020-04-08 at 22:13 +1000, Michael Ellerman wrote: [...] > Added context: >=20 > printk(KERN_EMERG "Sending IPI to other CPUs\n"); >=20 > if (crash_wake_offline) > ncpus =3D num_present_cpus() - 1; >=20 > > =20 > > crash_send_ipi(crash_ipi_callback); > > smp_wmb(); > > + printk_nmi_enter(); > =20 > Why did you decide to put it there, rather than at the start of > default_machine_crash_shutdown() like I did? >=20 > The printk() above could have already deadlocked if another CPU is stuck > with the logbuf lock held. Oh, I thought the CPUs would start crashing after crash_send_ipi(), so only printk() after that would possibly deadlock. I was not able to see how the printk() above would deadlock, but I see no problem adding that at the start of the function. Best regards, Leonardo Bras --=-lPjFWmObu0CMRxkrP/CR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEMdeUgIzgjf6YmUyOlQYWtz9SttQFAl6OGuIACgkQlQYWtz9S ttRQRg/+PovdIjJ5SBFZ1ufMi08FG6Ve7IN2VW3eVtItUXeHSe9o28GwLxTnUXJy TRUc1gVx8kUUEhnnKSvrrXyRTPJ/Z7LDEzvvo7o1M0s6buIHvbw8MZQUGSq5l2Sq wXNYeApRc7eSvF0mkBs4TZyPu4E5a22RI7SBHMouXqIxpOe4VXwDaEIZ7BOmc8lm s6+7EBZt1tI6n6ktHMxqN0GaYr18xWoz0hEscyULb++nGyQPMww8JQBJo9kToV7Q ziUpy1IJahKLUrIIxt1CZf3qBaAxO9GbVNEyfDtBEs1nThSJ1eweWk0bwAUJF8ll SRfAWcmBfvq3YFgGcWtcf9P1SOVbRJC6fFuaNbV9KP0gzJ8I4JyrA1sIhgIYkKqh UzlS15B2JHZBAFuT6J1oAofaP0+hooRipiloeoVhqBH0483jc/EjQS8u96bjgiBS AZyr5QjTfEINdvXar23uddbWymLPjh+IPNZAjK+goi0NdIjyHsyHgtz78XaR6q2M 06YOhmfFi2P9p30jaAqN6+7b4R50M61R+L1fTtzEWgb+xUe1HyKM7j/ff594f6M/ AZj16bSZtBMtQSp0q4DK/m0d8XXvwy2Hb0ABJiRhCSLxXvCfMEPHVtK9Xqn+JhEj XXH4XsARkrl9EQ94RhbUZQ55Y4Yga2F0+PI7dQvcc37KNlTgKo0= =pJkd -----END PGP SIGNATURE----- --=-lPjFWmObu0CMRxkrP/CR--