[3.13.y-ckt stable] Patch "nfs: don't call blocking operations while !TASK_RUNNING" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    nfs: don't call blocking operations while !TASK_RUNNING

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt18.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 2cc6ed1b42411ceb375410f0685ad00a2eb77632 Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton at primarydata.com>
Date: Wed, 14 Jan 2015 13:08:57 -0500
Subject: nfs: don't call blocking operations while !TASK_RUNNING

commit 6ffa30d3f734d4f6b478081dfc09592021028f90 upstream.

Bruce reported seeing this warning pop when mounting using v4.1:

     ------------[ cut here ]------------
     WARNING: CPU: 1 PID: 1121 at kernel/sched/core.c:7300 __might_sleep+0xbd/0xd0()
    do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff810ff58f>] prepare_to_wait+0x2f/0x90
    Modules linked in: rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd grace sunrpc fscache ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hwdep snd_pcm snd_timer ppdev joydev snd virtio_console virtio_balloon pcspkr serio_raw parport_pc parport pvpanic floppy soundcore i2c_piix4 virtio_blk virtio_net qxl drm_kms_helper ttm drm virtio_pci virtio_ring ata_generic virtio pata_acpi
    CPU: 1 PID: 1121 Comm: nfsv4.1-svc Not tainted 3.19.0-rc4+ #25
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140709_153950- 04/01/2014
     0000000000000000 000000004e5e3f73 ffff8800b998fb48 ffffffff8186ac78
     0000000000000000 ffff8800b998fba0 ffff8800b998fb88 ffffffff810ac9da
     ffff8800b998fb68 ffffffff81c923e7 00000000000004d9 0000000000000000
    Call Trace:
     [<ffffffff8186ac78>] dump_stack+0x4c/0x65
     [<ffffffff810ac9da>] warn_slowpath_common+0x8a/0xc0
     [<ffffffff810aca65>] warn_slowpath_fmt+0x55/0x70
     [<ffffffff810ff58f>] ? prepare_to_wait+0x2f/0x90
     [<ffffffff810ff58f>] ? prepare_to_wait+0x2f/0x90
     [<ffffffff810dd2ad>] __might_sleep+0xbd/0xd0
     [<ffffffff8124c973>] kmem_cache_alloc_trace+0x243/0x430
     [<ffffffff810d941e>] ? groups_alloc+0x3e/0x130
     [<ffffffff810d941e>] groups_alloc+0x3e/0x130
     [<ffffffffa0301b1e>] svcauth_unix_accept+0x16e/0x290 [sunrpc]
     [<ffffffffa0300571>] svc_authenticate+0xe1/0xf0 [sunrpc]
     [<ffffffffa02fc564>] svc_process_common+0x244/0x6a0 [sunrpc]
     [<ffffffffa02fd044>] bc_svc_process+0x1c4/0x260 [sunrpc]
     [<ffffffffa03d5478>] nfs41_callback_svc+0x128/0x1f0 [nfsv4]
     [<ffffffff810ff970>] ? wait_woken+0xc0/0xc0
     [<ffffffffa03d5350>] ? nfs4_callback_svc+0x60/0x60 [nfsv4]
     [<ffffffff810d45bf>] kthread+0x11f/0x140
     [<ffffffff810ea815>] ? local_clock+0x15/0x30
     [<ffffffff810d44a0>] ? kthread_create_on_node+0x250/0x250
     [<ffffffff81874bfc>] ret_from_fork+0x7c/0xb0
     [<ffffffff810d44a0>] ? kthread_create_on_node+0x250/0x250
    ---[ end trace 675220a11e30f4f2 ]---

nfs41_callback_svc does most of its work while in TASK_INTERRUPTIBLE,
which is just wrong. Fix that by finishing the wait immediately if we've
found that the list has something on it.

Also, we don't expect this kthread to accept signals, so we should be
using a TASK_UNINTERRUPTIBLE sleep instead. That however, opens us up
hung task warnings from the watchdog, so have the schedule_timeout
wake up every 60s if there's no callback activity.

Reported-by: "J. Bruce Fields" <bfields at fieldses.org>
Signed-off-by: Jeff Layton <jlayton at primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust at primarydata.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/nfs/callback.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 073b4cf..0a2016b 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -128,22 +128,24 @@ nfs41_callback_svc(void *vrqstp)
 		if (try_to_freeze())
 			continue;

-		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
+		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_UNINTERRUPTIBLE);
 		spin_lock_bh(&serv->sv_cb_lock);
 		if (!list_empty(&serv->sv_cb_list)) {
 			req = list_first_entry(&serv->sv_cb_list,
 					struct rpc_rqst, rq_bc_list);
 			list_del(&req->rq_bc_list);
 			spin_unlock_bh(&serv->sv_cb_lock);
+			finish_wait(&serv->sv_cb_waitq, &wq);
 			dprintk("Invoking bc_svc_process()\n");
 			error = bc_svc_process(serv, req, rqstp);
 			dprintk("bc_svc_process() returned w/ error code= %d\n",
 				error);
 		} else {
 			spin_unlock_bh(&serv->sv_cb_lock);
-			schedule();
+			/* schedule_timeout to game the hung task watchdog */
+			schedule_timeout(60 * HZ);
+			finish_wait(&serv->sv_cb_waitq, &wq);
 		}
-		finish_wait(&serv->sv_cb_waitq, &wq);
 	}
 	return 0;
 }
--
1.9.1