Date:   Fri, 8 Nov 2019 19:15:16 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH 1/2] list: add hlist_unhashed_lockless()

On Fri, Nov 8, 2019 at 3:42 PM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> On Fri, Nov 08, 2019 at 12:17:49PM -0800, Eric Dumazet wrote:
> > On Fri, Nov 8, 2019 at 11:24 AM Paul E. McKenney <paulmck@...nel.org> wrote:
> > >
> > > On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote:
> > > > We would like to use hlist_unhashed() from timer_pending(),
> > > > which runs without protection of a lock.
> > > >
> > > > Note that other callers might also want to use this variant.
> > > >
> > > > Instead of forcing a READ_ONCE() for all hlist_unhashed()
> > > > callers, add a new helper with an explicit _lockless suffix
> > > > in the name to better document what is going on.
> > > >
> > > > Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head()
> > > > and hlist_add_before()/hlist_add_behind() to pair with
> > > > the READ_ONCE().
> > > >
> > > > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > > > Cc: "Paul E. McKenney" <paulmck@...nel.org>
> > > > Cc: Thomas Gleixner <tglx@...utronix.de>
> > >
> > > I have queued this, but if you prefer it go some other way:
> > >
> > > Acked-by: Paul E. McKenney <paulmck@...nel.org>
> > >
> > > But shouldn't the uses in include/linux/rculist.h also be converted
> > > into the patch below?  If so, I will squash the following into your
> > > patch.
> > >
> > >                                                 Thanx, Paul
> > >
> > > ------------------------------------------------------------------------
> >
> > Agreed, thanks for the addition of this Paul.
>
> Very good, squashed and pushed, thank you!
>

I have another KCSAN report of a bug that will force us to use
hlist_unhashed_lockless() from sk_unhashed()

(Meaning we also need to add some WRITE_ONCE() annotations to
include/linux/list_nulls.h )

BUG: KCSAN: data-race in inet_unhash / inet_unhash

write to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 1:
 __hlist_nulls_del include/linux/list_nulls.h:88 [inline]
 hlist_nulls_del_init_rcu include/linux/rculist_nulls.h:36 [inline]
 __sk_nulls_del_node_init_rcu include/net/sock.h:676 [inline]
 inet_unhash+0x38f/0x4a0 net/ipv4/inet_hashtables.c:612
 tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
 tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
 tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
 tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
 tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
 tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
 arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
 default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
 cpuidle_idle_call kernel/sched/idle.c:154 [inline]
 do_idle+0x1af/0x280 kernel/sched/idle.c:263
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
 start_secondary+0x208/0x260 arch/x86/kernel/smpboot.c:264
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

read to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 0:
 sk_unhashed include/net/sock.h:607 [inline]
 inet_unhash+0x3d/0x4a0 net/ipv4/inet_hashtables.c:592
 tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
 tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
 tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
 tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
 tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
 tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
 arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
 default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
 cpuidle_idle_call kernel/sched/idle.c:154 [inline]
 do_idle+0x1af/0x280 kernel/sched/idle.c:263
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
 rest_init+0xec/0xf6 init/main.c:452
 arch_call_rest_init+0x17/0x37
 start_kernel+0x838/0x85e init/main.c:786
 x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490
 x86_64_start_kernel+0x72/0x76 arch/x86/kernel/head64.c:471
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011

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