Without this patch kernel crashes after:
1) start new netns
# unshare -m -n
2) start nfsd inside
# mount -t nfsd nfsd /proc/fs/nfsd
# echo 1 > /proc/fs/nfsd/threads
3) stop nfsd
# echo 0 > /proc/fs/nfsd/threads
4) destroy netns
# logout (exit fromshell executed by unshare)
[103026.179908] NFSD: starting 90-second grace period (net ffff8eeeb07949c0) <<< start nfsd
[103029.839058] nfsd: last server has exited, flushing export cache <<< stop nfsd
[103034.305184] ------------[ cut here ]------------ <<< destroy netns
[103034.305835] kernel BUG at fs/nfs_common/grace.c:111!
[103034.306132] invalid opcode: 0000 [#1] SMP
[103034.306392] Modules linked in: binfmt_misc nfsd auth_rpcgss nfs_acl lockd grace ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ip_set nfnetlink ebtable_nat ebtable_broute bridge stp llc ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_raw iptable_security ebtable_filter ebtables ip6table_filter ip6_tables sunrpc crct10dif_pclmul crc32_pclmul ghash_clmulni_intel joydev i2c_piix4 ppdev parport_pc pvpanic virtio_balloon parport pcspkr xfs libcrc32c virtio_console virtio_net virtio_scsi bochs_drm drm_kms_helper crc32c_intel ttm drm serio_raw virtio_pci virtio_ring virtio ata_generic pata_acpi floppy
[103034.307115] CPU: 3 PID: 3441 Comm: kworker/u16:2 Tainted: G W 4.14.0-rc6+ #2
[103034.307115] Hardware name: Virtuozzo KVM, BIOS 1.9.1-5.3.2.vz7.7 04/01/2014
[103034.307115] Workqueue: netns cleanup_net
[103034.307115] task: ffff8eeefcb9d040 task.stack: ffff9cf8816c4000
[103034.307115] RIP: 0010:grace_exit_net+0x24/0x30 [grace]
[103034.307115] RSP: 0018:ffff9cf8816c7de0 EFLAGS: 00010283
[103034.307115] RAX: ffff8eeeca139768 RBX: ffff8eeeb07949c0 RCX: fffff997000c6500
[103034.307115] RDX: ffff8eeee282cad0 RSI: ffffffffc07b9020 RDI: ffff8eeeb07949c0
[103034.307115] RBP: ffff9cf8816c7de0 R08: ffff8eee83195038 R09: 00000001001b0019
[103034.307115] R10: ffff9cf8816c7d60 R11: 0000000000000000 R12: ffff9cf8816c7e38
[103034.307115] R13: ffffffffc07b9018 R14: ffffffffc07b9020 R15: 00000000ffffffff
[103034.307115] FS: 0000000000000000(0000) GS:ffff8eeeffcc0000(0000) knlGS:0000000000000000
[103034.307115] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[103034.307115] CR2: 00005632ccdcaa98 CR3: 000000000be09002 CR4: 00000000001606e0
[103034.307115] Call Trace:
[103034.307115] ops_exit_list.isra.6+0x38/0x60
[103034.307115] cleanup_net+0x1e2/0x2e0
[103034.307115] process_one_work+0x193/0x3c0
[103034.307115] worker_thread+0x35/0x3b0
[103034.307115] kthread+0x125/0x140
[103034.307115] ? process_one_work+0x3c0/0x3c0
[103034.307115] ? kthread_park+0x60/0x60
[103034.307115] ? kthread_park+0x60/0x60
[103034.307115] ret_from_fork+0x25/0x30
[103034.307115] Code: 1f 84 00 00 00 00 00 0f 1f 44 00 00 8b 15 c9 22 00 00 48 8b 87 78 12 00 00 48 8b 04 d0 48 8b 10 48 39 d0 75 02 f3 c3 55 48 89 e5 <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 8b 15 98
[103034.307115] RIP: grace_exit_net+0x24/0x30 [grace] RSP: ffff9cf8816c7de0
On 2017-11-02 13:03, Vasily Averin wrote:
> Commit efda760fe95ea ("lockd: fix lockd shutdown race") is incorrect,
> it removes lockd_manager and disarm grace_period_end for init_net only.
>
> If nfsd was started from another net namespace lockd_up_net() calls
> set_grace_period() that adds lockd_manager into per-netns list
> and queues grace_period_end delayed work.
>
> These action should be reverted in lockd_down_net().
> Otherwise it can lead to double list_add on after restart nfsd in netns,
> and to use-after-free if non-disarmed delayed work will be executed after netns destroy.
>
> Fixes commit efda760fe95e ("lockd: fix lockd shutdown race")
>
> Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
> ---
> fs/lockd/svc.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
> index c1573860..809cbcc 100644
> --- a/fs/lockd/svc.c
> +++ b/fs/lockd/svc.c
> @@ -277,6 +277,8 @@ static void lockd_down_net(struct svc_serv *serv, struct net *net)
> if (ln->nlmsvc_users) {
> if (--ln->nlmsvc_users == 0) {
> nlm_shutdown_hosts_net(net);
> + cancel_delayed_work_sync(&ln->grace_period_end);
> + locks_end_grace(&ln->lockd_manager);
> svc_shutdown_net(serv, net);
> dprintk("lockd_down_net: per-net data destroyed; net=%p\n", net);
> }
>
--
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