From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfram Sang Subject: Re: [PATCH resend] can: rcar_canfd: fix possible IRQ storm on high load Date: Wed, 26 Jun 2019 15:12:51 +0200 Message-ID: <20190626131251.GB801@ninjato> References: <20190626130848.6671-1-nikita.yoush@cogentembedded.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="IrhDeMKUP4DT/M7F" Return-path: Content-Disposition: inline In-Reply-To: <20190626130848.6671-1-nikita.yoush@cogentembedded.com> Sender: netdev-owner@vger.kernel.org To: Nikita Yushchenko , Ramesh Shanmugasundaram Cc: Wolfgang Grandegger , Marc Kleine-Budde , "David S. Miller" , Simon Horman , Wolfram Sang , linux-can@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Artemi Ivanov , Sergei Shtylyov List-Id: linux-can.vger.kernel.org --IrhDeMKUP4DT/M7F Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Jun 26, 2019 at 04:08:48PM +0300, Nikita Yushchenko wrote: > We have observed rcar_canfd driver entering IRQ storm under high load, > with following scenario: > - rcar_canfd_global_interrupt() in entered due to Rx available, > - napi_schedule_prep() is called, and sets NAPIF_STATE_SCHED in state > - Rx fifo interrupts are masked, > - rcar_canfd_global_interrupt() is entered again, this time due to > error interrupt (e.g. due to overflow), > - since scheduled napi poller has not yet executed, condition for calling > napi_schedule_prep() from rcar_canfd_global_interrupt() remains true, > thus napi_schedule_prep() gets called and sets NAPIF_STATE_MISSED flag > in state, > - later, napi poller function rcar_canfd_rx_poll() gets executed, and > calls napi_complete_done(), > - due to NAPIF_STATE_MISSED flag in state, this call does not clear > NAPIF_STATE_SCHED flag from state, > - on return from napi_complete_done(), rcar_canfd_rx_poll() unmasks Rx > interrutps, > - Rx interrupt happens, rcar_canfd_global_interrupt() gets called > and calls napi_schedule_prep(), > - since NAPIF_STATE_SCHED is set in state at this time, this call > returns false, > - due to that false return, rcar_canfd_global_interrupt() returns > without masking Rx interrupt > - and this results into IRQ storm: unmasked Rx interrupt happens again > and again is misprocessed in the same way. >=20 > This patch fixes that scenario by unmasking Rx interrupts only when > napi_complete_done() returns true, which means it has cleared > NAPIF_STATE_SCHED in state. >=20 > Signed-off-by: Nikita Yushchenko CCing the driver author... > --- > drivers/net/can/rcar/rcar_canfd.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) >=20 > diff --git a/drivers/net/can/rcar/rcar_canfd.c b/drivers/net/can/rcar/rca= r_canfd.c > index 05410008aa6b..de34a4b82d4a 100644 > --- a/drivers/net/can/rcar/rcar_canfd.c > +++ b/drivers/net/can/rcar/rcar_canfd.c > @@ -1508,10 +1508,11 @@ static int rcar_canfd_rx_poll(struct napi_struct = *napi, int quota) > =20 > /* All packets processed */ > if (num_pkts < quota) { > - napi_complete_done(napi, num_pkts); > - /* Enable Rx FIFO interrupts */ > - rcar_canfd_set_bit(priv->base, RCANFD_RFCC(ridx), > - RCANFD_RFCC_RFIE); > + if (napi_complete_done(napi, num_pkts)) { > + /* Enable Rx FIFO interrupts */ > + rcar_canfd_set_bit(priv->base, RCANFD_RFCC(ridx), > + RCANFD_RFCC_RFIE); > + } > } > return num_pkts; > } > --=20 > 2.11.0 >=20 --IrhDeMKUP4DT/M7F Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEOZGx6rniZ1Gk92RdFA3kzBSgKbYFAl0Tb1MACgkQFA3kzBSg KbaLaA//Wza8AWpDytatCR4+YVO8bhaKfX8Cxpi3bmnFG9stqfjA5qAiC9ADINPw mERmNC/IfW5GstYjHrQK7tsgThSoTb1326jm/Gg1KScq5cwos/SIsRV0VE6k006c UWHc/HIqSyDN8ILvh/n1tsUMFWz+KEtFCqqrNLsLX3zRnyJj3CIfqdG8Crby2MzQ jy1NVgUsWpj7VEZ19BkUTHfR3sMWvQGkqWIm+N0uNz+vcErnrNKon3eVt4UrysiZ 2+/5qXNjcJS2KtEu4O2StunxA1vftTOX29p7dm2qCXlVN5oAq8HQQ/os/ucMvxWm ZSKqXxM7sVl2X1ZY2d8057XAnqTpgoz2cFoI5VznM/3PJ3ykG453K2qX3qon1hBl bgLAWRafnusja2eafqwzcjjymDu6aTFUAszodA+CPTMdM+9TjLZaZTKaoMVGbHqY rINTTbisLKKRqQ+cPPD9l4M5iQ1QyJr+lQledI4M9XzJn2as2B5OuUw06LgKPpBC FKIvuUuCxI6yIB5f1l2MXfRBnmTnNvLpmhi2SiRVMfaL8FXAzdlLMLJ+PD0K3LAj c7RLt0+q3TL72pPdXOBUtNB2ukyGRH7Rbmjg3cwIumyIQqC4v32tA0FTYdg+l5gy ZxHjMzQczyqroya5caDanJVNPWiDrZh39Y8Gy8ovE+tYOBXMXQ8= =ssZ5 -----END PGP SIGNATURE----- --IrhDeMKUP4DT/M7F--