From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gao feng Subject: Re: [PATCH] net, cgroup: Fix boot failure due to iteration of uninitialized list Date: Mon, 23 Jul 2012 09:15:05 +0800 Message-ID: <500CA599.6030907@cn.fujitsu.com> References: <20120719162532.23505.85946.stgit@srivatsabhat.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: nhorman@tuxdriver.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, mark.d.rustad@intel.com, john.r.fastabend@intel.com, lizefan@huawei.com To: "Srivatsa S. Bhat" , eric.dumazet@gmail.com, davem@davemloft.net Return-path: In-Reply-To: <20120719162532.23505.85946.stgit@srivatsabhat.in.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org =E4=BA=8E 2012=E5=B9=B407=E6=9C=8820=E6=97=A5 00:27, Srivatsa S. Bhat =E5= =86=99=E9=81=93: > After commit ef209f15 (net: cgroup: fix access the unallocated memory= in > netprio cgroup), boot fails with the following NULL pointer dereferen= ce: >=20 > Initializing cgroup subsys devices > Initializing cgroup subsys freezer > Initializing cgroup subsys net_cls > Initializing cgroup subsys blkio > Initializing cgroup subsys perf_event > Initializing cgroup subsys net_prio > BUG: unable to handle kernel NULL pointer dereference at 000000000000= 0698 > IP: [] cgrp_create+0xf6/0x190 > PGD 0 > Oops: 0000 [#1] SMP > CPU 0 > Modules linked in: >=20 > Pid: 0, comm: swapper/0 Not tainted 3.5.0-rc7-mandeep #1 IBM IBM Syst= em x -[7870C4Q]-/68Y8033 > RIP: 0010:[] [] cgrp_create+0xf6= /0x190 > RSP: 0000:ffffffff81a01ea8 EFLAGS: 00010213 > RAX: 0000000000000000 RBX: ffffffffffffff10 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: 0000000000000246 RDI: ffffffff81aa70a0 > RBP: ffffffff81a01ed8 R08: 0000000000000000 R09: 0000000000000000 > R10: ffff8808ff8641c0 R11: 6e697a696c616974 R12: 0000000000000001 > R13: ffff8808ff8641c0 R14: 0000000000000000 R15: 0000000000093970 > FS: 0000000000000000(0000) GS:ffff8808ffc00000(0000) knlGS:000000000= 0000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > CR2: 0000000000000698 CR3: 0000000001a0b000 CR4: 00000000000006b0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Process swapper/0 (pid: 0, threadinfo ffffffff81a00000, task ffffffff= 81a13420) > Stack: > ffffffff81a01eb8 ffffffff818060ff ffffffff81d75ec8 ffffffff81aa8960 > ffffffff81aa8960 ffffffff81b4c2c0 ffffffff81a01ef8 ffffffff81b1cb78 > 0000000000000018 0000000000000048 ffffffff81a01f18 ffffffff81b1ce13 > Call Trace: > [] cgroup_init_subsys+0x83/0x169 > [] cgroup_init+0x36/0x119 > [] start_kernel+0x3ba/0x3ef > [] ? kernel_init+0x27b/0x27b > [] x86_64_start_reservations+0x131/0x136 > [] x86_64_start_kernel+0x103/0x112 > Code: 01 48 3d f8 e1 ec 81 48 8d 98 10 ff ff ff 75 1b eb 73 0f 1f 00 = 48 8b 83 f0 00 00 00 48 3d f8 e1 ec 81 48 8d 98 10 ff ff ff 74 5a <48> = 8b 83 88 07 00 00 48 85 c0 74 de 44 3b 60 10 76 d8 44 89 e6 > RIP [] cgrp_create+0xf6/0x190 > RSP > CR2: 0000000000000698 > ---[ end trace a7919e7f17c0a725 ]--- > Kernel panic - not syncing: Attempted to kill the idle task! >=20 > The code corresponds to: >=20 > update_netdev_tables(): > for_each_netdev(&init_net, dev) { > map =3D rtnl_dereference(dev->priomap); <---- HERE >=20 >=20 > The list head is initialized in netdev_init(), which is called much > later than cgrp_create(). So the problem is that we are calling > update_netdev_tables() way too early (in cgrp_create()), which will > end up traversing the not-yet-circular linked list. So at some point, > the dev pointer will become NULL and hence dev->priomap becomes an > invalid access. >=20 > To fix this, just remove the update_netdev_tables() function entirely= , > since it appears that write_update_netdev_table() will handle things > just fine. The reason I add update_netdev_tables in cgrp_create is to avoid additi= onal bound checkings when we accessing the dev->priomap.priomap. Eric,can we revert this commit 91c68ce2b26319248a32d7baa1226f819d283758= now? I think it's safe enough to access priomap without bound check. Thanks