On Tue, 21 Mar 2017, Dave Jones wrote:
> On Tue, Mar 21, 2017 at 08:25:39PM +0100, Thomas Gleixner wrote:
>
> > > I just hit this while fuzzing..
> > >
> > > general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> > > CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.11.0-rc2-think+ #1
> > > task: ffff88017f0ed440 task.stack: ffffc90000094000
> > > RIP: 0010:run_timer_softirq+0x15f/0x700
> > > RSP: 0018:ffff880507c03ec8 EFLAGS: 00010086
> > > RAX: dead000000000200 RBX: ffff880507dd0d00 RCX: 0000000000000002
> > > RDX: ffff880507c03ed0 RSI: 00000000ffffffff RDI: ffffffff8204b3a0
> > > RBP: ffff880507c03f48 R08: ffff880507dd12d0 R09: ffff880507c03ed8
> > > R10: ffff880507dd0db0 R11: 0000000000000000 R12: ffffffff8215cc38
> > > R13: ffff880507c03ed0 R14: ffffffff82005188 R15: ffff8804b55491a8
> > > FS: 0000000000000000(0000) GS:ffff880507c00000(0000)
> knlGS:0000000000000000
> > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 0000000000000004 CR3: 0000000005011000 CR4: 00000000001406e0
> > > Call Trace:
> > > <IRQ>
> > > ? clockevents_program_event+0x47/0x120
> > > __do_softirq+0xbf/0x5b1
> > > irq_exit+0xb5/0xc0
> > > smp_apic_timer_interrupt+0x3d/0x50
> > > apic_timer_interrupt+0x97/0xa0
> > > RIP: 0010:cpuidle_enter_state+0x12e/0x400
> > > RSP: 0018:ffffc90000097e40 EFLAGS: 00000202
> > > [CONT START] ORIG_RAX: ffffffffffffff10
> > > RAX: ffff88017f0ed440 RBX: ffffe8ffffa03cc8 RCX: 0000000000000001
> > > RDX: 20c49ba5e353f7cf RSI: 0000000000000001 RDI: ffff88017f0ed440
> > > RBP: ffffc90000097e80 R08: 00000000ffffffff R09: 0000000000000008
> > > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000005
> > > R13: ffffffff820b9338 R14: 0000000000000005 R15: ffffffff820b9320
> > > </IRQ>
> > > cpuidle_enter+0x17/0x20
> > > call_cpuidle+0x23/0x40
> > > do_idle+0xfb/0x200
> > > cpu_startup_entry+0x71/0x80
> > > start_secondary+0x16a/0x210
> > > start_cpu+0x14/0x14
> > > Code: 8b 05 ce 1b ef 7e 83 f8 03 0f 87 4e 01 00 00 89 c0 49 0f a3 04 24
> 0f 82 0a 01 00 00 49 8b 07 49 8b 57 08 48 85 c0 48 89 02 74 04 <48> 89 50 08
> 41 f6 47 2a 20 49 c7 47 08 00 00 00 00 48 89 df 48
> >
> > The timer which expires has timer->entry.next == POISON2 !
> >
> > it's a classic list corruption. The
> > bad news is that there is no trace of the culprit because that happens when
> > some other timer expires after some random amount of time.
> >
> > If that is reproducible, then please enable debugobjects. That should
> > pinpoint the culprit.
>
> It's net/smc. This recently had a similar bug with workqueues.
> (https://marc.info/?l=linux-kernel&m=148821582909541) fixed by
> 637fdbae60d6cb9f6e963c1079d7e0445c86ff7d
Fixed? It's not fixed by that commit. The workqueue code merily got a new
WARN_ON_ONCE(). But the underlying problem is still unfixed in net/smc
> so it's probably unsurprising that there are similar issues.
That one is related to workqueues:
> WARNING: CPU: 0 PID: 2430 at lib/debugobjects.c:289
> debug_print_object+0x87/0xb0
> ODEBUG: free active (active state 0) object type: timer_list hint:
> delayed_work_timer_fn+0x0/0x20
delayed_work_timer_fn() is what queues the work once the timer expires.
> CPU: 0 PID: 2430 Comm: trinity-c4 Not tainted 4.11.0-rc3-think+ #3
> Call Trace:
> dump_stack+0x68/0x93
> __warn+0xcb/0xf0
> warn_slowpath_fmt+0x5f/0x80
> ? debug_check_no_obj_freed+0xd9/0x260
> debug_print_object+0x87/0xb0
> ? work_on_cpu+0xd0/0xd0
> debug_check_no_obj_freed+0x219/0x260
> ? __sk_destruct+0x10d/0x1c0
> kmem_cache_free+0x9f/0x370
> __sk_destruct+0x10d/0x1c0
> sk_destruct+0x20/0x30
> __sk_free+0x43/0xa0
> sk_free+0x18/0x20
smc_release does at the end of the function:
if (smc->use_fallback) {
schedule_delayed_work(&smc->sock_put_work, TCP_TIMEWAIT_LEN);
} else if (sk->sk_state == SMC_CLOSED) {
smc_conn_free(&smc->conn);
schedule_delayed_work(&smc->sock_put_work,
SMC_CLOSE_SOCK_PUT_DELAY);
}
sk->sk_prot->unhash(sk);
release_sock(sk);
sock_put(sk);
sock_put(sk)
{
if (atomic_dec_and_test(&sk->sk_refcnt))
sk_free(sk);
}
That means either smc_release() queued delayed work or it was already
queued.
But in neither case it holds an extra refcount on sk. Otherwise sock_put()
would not end up in sk_free().
Thanks,
tglx
