From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: Problem with patch "make nlmsg_end() and genlmsg_end() void" Date: Tue, 09 Jun 2015 14:34:24 +0100 Message-ID: <1433856864.19447.25.camel@infradead.org> References: <01A82AB9-6ABD-4AD0-9CBC-628091569DB0@holtmann.org> <20150118.233722.226468667930444145.davem@davemloft.net> <1428494602.9010.11.camel@infradead.org> <1428498482.2809.10.camel@sipsolutions.net> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-vKnnpEgphuaQt2TKu1BK" Cc: David Miller , torvalds@linux-foundation.org, marcel@holtmann.org, sfeldma@gmail.com, netdev@vger.kernel.org, teg@jklm.no To: Johannes Berg Return-path: Received: from casper.infradead.org ([85.118.1.10]:50891 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753080AbbFINe3 (ORCPT ); Tue, 9 Jun 2015 09:34:29 -0400 In-Reply-To: <1428498482.2809.10.camel@sipsolutions.net> Sender: netdev-owner@vger.kernel.org List-ID: --=-vKnnpEgphuaQt2TKu1BK Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2015-04-08 at 15:08 +0200, Johannes Berg wrote: > On Wed, 2015-04-08 at 13:03 +0100, David Woodhouse wrote: >=20 > > I'm not sure if this is entirely fixed. In Fedora 22 (4.0.0-rc5-git4) > > I'm occasionally seeing glibc deadlock in __check_pf() on a netlink > > recvmsg(), here: > > https://sourceware.org/git/?p=3Dglibc.git;a=3Dblob;f=3Dsysdeps/unix/sys= v/linux/check_pf.c;h=3D162606d7;hb=3Dglibc-2.21#l166 > >=20 > > As I understand it, this shouldn't happen. Even if messages are > > dropped (which surely shouldn't happen as often as I'm seeing this), > > glibc should get ENOBUFS from the recvmsg() call. > >=20 > > https://bugzilla.redhat.com/show_bug.cgi?id=3D1209433 > >=20 > > I haven't bisected and proved that it *was* this commit which > > introduced the problem, as it only happens after a day or two of > > running Evolution and I haven't managed to trigger it more reliably. >=20 > I don't see the connection to this change. >=20 > The issue with my patch was that some code for NLM_F_DUMP would have > this pattern: >=20 > int fill_function(...) > { > ... > return nlmsg_end(...); > } >=20 > loop (...) { > if (fill_function() <=3D 0) > break; /* continue in next dump */ > } >=20 > and that all had to be converted to be just "< 0" now. >=20 > Additionally, the failure mode of this was the process running out of > memory due to receiving the same results over and over again - does that > happen for you? It seems it was stuck in recvmsg(), but that may just be > a side effect of happening to interrupt at that point? >=20 I don't think the problem was introduced by your change. At=20 https://github.com/nahi/httpclient/issues/232 it seems to have been observed even in November of last year. I've added some debugging, and it seems that when it deadlocks, glibc doesn't get *any* response to its RTM_GETADDR request. I know we'd get ENOBUFS is a *response* was dropped... but what about when the request itself is dropped? Does userspace get any hint of that? Is this purely a glibc bug, for assuming its request got delivered and unconditionally waiting for a response? I don't know why it suddenly started happening to me in the 4.0 kernel when I'd never seen it before, but it's still happening. I've put a poll() in the glibc code (referenced above), and made it fail after a 5 -second timeout. That will at least prevent me from throwing my computer out the window for the time being... --=20 dwmw2 --=-vKnnpEgphuaQt2TKu1BK Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIISjjCCBicw ggUPoAMCAQICAw3vNzANBgkqhkiG9w0BAQUFADCBjDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0 YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcx ODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENB MB4XDTE1MDUwNTA5NDM0MVoXDTE2MDUwNTA5NTMzNlowQjEcMBoGA1UEAwwTZHdtdzJAaW5mcmFk ZWFkLm9yZzEiMCAGCSqGSIb3DQEJARYTZHdtdzJAaW5mcmFkZWFkLm9yZzCCASIwDQYJKoZIhvcN AQEBBQADggEPADCCAQoCggEBAMkbm9kPbx1j/X4RVyf/pPKSYwelcco69TvnQQbKM8m8xkWjXJI1 jpJ1jMaGUZGFToINMSZi7lZawUozudWbXSKy1SikENSTJHffsdRAIlsp+hR8vWvjsKUry6sEdqPG doa5RY7+N4WRusWZDYW/RRWE6i9EL9qV86CVPYqw22UBOUw4/j/HVGCV6TSB8yE5iEwhk/hUuzRr 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