From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754040Ab2K1KT0 (ORCPT ); Wed, 28 Nov 2012 05:19:26 -0500 Received: from merlin.infradead.org ([205.233.59.134]:48200 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753856Ab2K1KTZ (ORCPT ); Wed, 28 Nov 2012 05:19:25 -0500 Message-ID: <1354097960.21562.41.camel@shinybook.infradead.org> Subject: Re: [PATCH v3 8/7] pppoatm: fix missing wakeup in pppoatm_send() From: David Woodhouse To: Krzysztof Mazur Cc: chas williams - CONTRACTOR , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net Date: Wed, 28 Nov 2012 10:19:20 +0000 In-Reply-To: <20121128095843.GA8974@shrek.podlesie.net> References: <201211112257.qABMvhP4021769@thirdoffive.cmf.nrl.navy.mil> <1354022867.26346.334.camel@shinybook.infradead.org> <20121127102333.68ac3234@thirdoffive.cmf.nrl.navy.mil> <1354063697.21562.4.camel@shinybook.infradead.org> <20121128081237.GA30488@shrek.podlesie.net> <1354094649.21562.34.camel@shinybook.infradead.org> <20121128095843.GA8974@shrek.podlesie.net> Content-Type: multipart/signed; micalg="sha1"; protocol="application/x-pkcs7-signature"; boundary="=-VyX/Gs/GPavwzdwUwmHr" X-Mailer: Evolution 3.6.1 (3.6.1-1.fc18) Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-VyX/Gs/GPavwzdwUwmHr Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2012-11-28 at 10:58 +0100, Krzysztof Mazur wrote: > ok, I think that we should just drop that patch, with test_bit() > I think it's no longer an optimization. After another cup of tea, it now uses test_and_clear_bit()... and doesn't break the carefully crafted handling of the BLOCKED bit in the normal flow control case, by setting it at the nospace: label! =46rom b2cf6a466697ecf19061cb11b8f4ec5bb381550a Mon Sep 17 00:00:00 2001 From: David Woodhouse Date: Wed, 28 Nov 2012 10:15:05 +0000 Subject: [PATCH] pppoatm: optimise PPP channel wakeups after sock_owned_by_= user() We don't need to schedule the wakeup tasklet on *every* unlock; only if we actually blocked the channel in the first place. Signed-off-by: David Woodhouse --- net/atm/pppoatm.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c index 446a7f0..172e44e 100644 --- a/net/atm/pppoatm.c +++ b/net/atm/pppoatm.c @@ -113,7 +113,17 @@ static void pppoatm_release_cb(struct atm_vcc *atmvcc) { struct pppoatm_vcc *pvcc =3D atmvcc_to_pvcc(atmvcc); =20 - tasklet_schedule(&pvcc->wakeup_tasklet); + /* + * As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because + * the wakeup *can't* race with pppoatm_send(). They both hold the PPP + * channel's ->downl lock. And the potential race with *setting* it, + * which leads to the double-check dance in pppoatm_may_send(), doesn't + * exist here. In the sock_owned_by_user() case in pppoatm_send(), we + * set the BLOCKED bit while the socket is still locked. We know that + * ->release_cb() can't be called until that's done. + */ + if (test_and_clear_bit(BLOCKED, &pvcc->blocked)) + tasklet_schedule(&pvcc->wakeup_tasklet); if (pvcc->old_release_cb) pvcc->old_release_cb(atmvcc); } @@ -292,8 +302,15 @@ static int pppoatm_send(struct ppp_channel *chan, stru= ct sk_buff *skb) =20 vcc =3D ATM_SKB(skb)->vcc; bh_lock_sock(sk_atm(vcc)); - if (sock_owned_by_user(sk_atm(vcc))) + if (sock_owned_by_user(sk_atm(vcc))) { + /* + * Needs to happen (and be flushed, hence test_and_) before we unlock + * the socket. It needs to be seen by the time our ->release_cb gets + * called. + */ + test_and_set_bit(BLOCKED, &pvcc->blocked); goto nospace; + } if (test_bit(ATM_VF_RELEASED, &vcc->flags) || test_bit(ATM_VF_CLOSE, &vcc->flags) || !test_bit(ATM_VF_READY, &vcc->flags)) { --=20 1.8.0 --=20 dwmw2 --=-VyX/Gs/GPavwzdwUwmHr Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIUbjCCBjQw ggQcoAMCAQICAR4wDQYJKoZIhvcNAQEFBQAwfTELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0YXJ0 Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcxKTAn BgNVBAMTIFN0YXJ0Q29tIENlcnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTA3MTAyNDIxMDE1NVoX DTE3MTAyNDIxMDE1NVowgYwxCzAJBgNVBAYTAklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSsw KQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0ZSBTaWduaW5nMTgwNgYDVQQDEy9TdGFy dENvbSBDbGFzcyAxIFByaW1hcnkgSW50ZXJtZWRpYXRlIENsaWVudCBDQTCCASIwDQYJKoZIhvcN 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