[#LU-6476] conf-sanity: test_53a Error: 'test failed to respond and timed out'

One of the tests nodes running test_53a()/thread_sanity()/lustre_rmmod got an Oops in _spin_lock_irqsave() with the following stack dumped on the Console :

13:04:49:BUG: unable to handle kernel NULL pointer dereference at (null)
13:04:49:IP: [<ffffffff8152cdcf>] _spin_lock_irqsave+0x1f/0x40
13:04:49:PGD 7985a067 PUD 7bb69067 PMD 0 
13:04:49:Oops: 0002 [#1] SMP 
13:04:49:last sysfs file: /sys/devices/system/cpu/possible
13:04:49:CPU 1 
13:04:49:Modules linked in: ptlrpc(-)(U) obdclass(U) ksocklnd(U) lnet(U) libcfs(U) sha512_generic nfs fscache nfsd lockd nfs_acl auth_rpcgss sunrpc exportfs autofs4 ib_ipoib rdma_ucm ib_ucm ib_uverbs ib_umad rdma_cm ib_cm iw_cm ib_sa ib_mad ib_core ib_addr ipv6 microcode virtio_balloon 8139too 8139cp mii i2c_piix4 i2c_core ext3 jbd mbcache virtio_blk virtio_pci virtio_ring virtio pata_acpi ata_generic ata_piix dm_mirror dm_region_hash dm_log dm_mod [last unloaded: ptlrpc_gss]
13:04:49:
13:04:49:Pid: 9166, comm: rmmod Not tainted 2.6.32-504.12.2.el6.x86_64 #1 Red Hat KVM
13:04:49:RIP: 0010:[<ffffffff8152cdcf>]  [<ffffffff8152cdcf>] _spin_lock_irqsave+0x1f/0x40
13:04:49:RSP: 0018:ffff88007b1c5db8  EFLAGS: 00010082
13:04:49:RAX: 0000000000010000 RBX: 0000000000000000 RCX: 0000000000000000
13:04:49:RDX: 0000000000000282 RSI: 0000000000000003 RDI: 0000000000000000
13:04:49:RBP: ffff88007b1c5db8 R08: ffff880079865540 R09: 0000000000000001
13:04:49:R10: 0000000000000000 R11: 0000000000000000 R12: ffff88007b900aa0
13:04:49:R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
13:04:49:FS:  00007f46301fe700(0000) GS:ffff880002300000(0000) knlGS:0000000000000000
13:04:49:CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
13:04:49:CR2: 0000000000000000 CR3: 000000007cb24000 CR4: 00000000000006e0
13:04:49:DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
13:04:49:DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
13:04:49:Process rmmod (pid: 9166, threadinfo ffff88007b1c4000, task ffff88007b900aa0)
13:04:49:Stack:
13:04:49: ffff88007b1c5df8 ffffffff8105bd02 ffff880078f849c0 0000000000000880
13:04:49:<d> ffff88007b900aa0 ffff88007b1c5e68 0000000000000000 0000000000000001
13:04:49:<d> ffff88007b1c5e08 ffffffffa0761cdf ffff88007b1c5e18 ffffffffa0743104
13:04:49:Call Trace:
13:04:49: [<ffffffff8105bd02>] __wake_up+0x32/0x70
13:04:49: [<ffffffffa0761cdf>] lnet_acceptor_stop+0x3f/0x50 [lnet]
13:04:49: [<ffffffffa0743104>] LNetNIFini+0x74/0x100 [lnet]
13:04:49: [<ffffffffa09ed775>] ptlrpc_ni_fini+0x135/0x1b0 [ptlrpc]
13:04:49: [<ffffffffa09ed803>] ptlrpc_exit_portals+0x13/0x20 [ptlrpc]
13:04:49: [<ffffffffa0a2fcaa>] ptlrpc_exit+0x22/0x38 [ptlrpc]
13:04:49: [<ffffffff810bcf14>] sys_delete_module+0x194/0x260
13:04:49: [<ffffffff810e5c87>] ? audit_syscall_entry+0x1d7/0x200
13:04:49: [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
13:04:49:Code: c9 c3 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 0f 1f 44 00 00 9c 58 0f 1f 44 00 00 48 89 c2 fa 66 0f 1f 44 00 00 b8 00 00 01 00 <f0> 0f c1 07 0f b7 c8 c1 e8 10 39 c1 74 0e f3 90 0f 1f 44 00 00 
13:04:49:RIP  [<ffffffff8152cdcf>] _spin_lock_irqsave+0x1f/0x40
13:04:49: RSP <ffff88007b1c5db8>
13:04:49:CR2: 0000000000000000

Looks like there is a race between lnet_acceptor_stop() execution and concurrent (and unexpected?) acceptor thread exit, where lnet_acceptor_stop() :

void
lnet_acceptor_stop(void)
{
        if (lnet_acceptor_state.pta_shutdown) /* not running */
                return;

        lnet_acceptor_state.pta_shutdown = 1;
        wake_up_all(sk_sleep(lnet_acceptor_state.pta_sock->sk));

        /* block until acceptor signals exit */
        wait_for_completion(&lnet_acceptor_state.pta_signal);
}

tries to wake-up all socket sleepers without protecting itself against acceptor thread concurent exit in lnet_acceptor() routine :

        }

        sock_release(lnet_acceptor_state.pta_sock);
        lnet_acceptor_state.pta_sock = NULL;

        CDEBUG(D_NET, "Acceptor stopping\n");

        /* unblock lnet_acceptor_stop() */
        complete(&lnet_acceptor_state.pta_signal);
        return 0;
}

where acceptor socket is released and its sk_sleep sleepers wait-queue is cleared under protection of sk_callback_lock RW-Lock in sock_orphan(). So seems that lnet_acceptor_stop() should better use, or implement the same behavior than, sock_def_wakeup() :

static void sock_def_wakeup(struct sock *sk)
{
        read_lock(&sk->sk_callback_lock);
        if (sk_has_sleeper(sk))
                wake_up_interruptible_all(sk->sk_sleep);
        read_unlock(&sk->sk_callback_lock);
}

instead of simply calling wake_up_all().
This may have been introduced by recent integration of patches to implement dynamic acceptor start/stop feature.
Will push a patch to give a try to my previous thought on how this can be fixed.

[LU-6476] conf-sanity: test_53a Error: 'test failed to respond and timed out' Created: 20/Apr/15 Updated: 11/Jul/15 Resolved: 11/Jul/15
Status:	Resolved
Project:	Lustre
Component/s:	None
Affects Version/s:	Lustre 2.8.0
Fix Version/s:	Lustre 2.8.0

[LU-6476] conf-sanity: test_53a Error: 'test failed to respond and timed out' Created: 20/Apr/15 Updated: 11/Jul/15 Resolved: 11/Jul/15