Messages in this thread Patch in this message | | | Date | Sat, 9 Nov 2019 10:53:36 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 1/2] list: add hlist_unhashed_lockless() |
| |
On Sat, Nov 09, 2019 at 09:54:40AM -0800, Paul E. McKenney wrote: > On Fri, Nov 08, 2019 at 07:15:16PM -0800, Eric Dumazet wrote: > > On Fri, Nov 8, 2019 at 3:42 PM Paul E. McKenney <paulmck@kernel.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@kernel.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@google.com> > > > > > > Cc: "Paul E. McKenney" <paulmck@kernel.org> > > > > > > Cc: Thomas Gleixner <tglx@linutronix.de> > > > > > > > > > > I have queued this, but if you prefer it go some other way: > > > > > > > > > > Acked-by: Paul E. McKenney <paulmck@kernel.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 > > Like this?
Hmmm... Do you also need this?
Thanx, Paul
------------------------------------------------------------------------
commit cf78c8772c9dc26a36c0e5eae1262cc396bbfb3f Author: Paul E. McKenney <paulmck@kernel.org> Date: Sat Nov 9 10:45:47 2019 -0800
rcu: Add a hlist_nulls_unhashed_lockless() function This commit adds an hlist_nulls_unhashed_lockless() to allow lockless checking for whether or note an hlist_nulls_node is hashed or not. While in the area, this commit also adds a docbook comment to the existing hlist_nulls_unhashed() function. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h index 1ecd356..fa6e847 100644 --- a/include/linux/list_nulls.h +++ b/include/linux/list_nulls.h @@ -56,11 +56,33 @@ static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr) return ((unsigned long)ptr) >> 1; } +/** + * hlist_nulls_unhashed - Has node been removed and reinitialized? + * @h: Node to be checked + * + * Not that not all removal functions will leave a node in unhashed state. + * For example, hlist_del_init_rcu() leaves the node in unhashed state, + * but hlist_nulls_del() does not. + */ static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h) { return !h->pprev; } +/** + * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized? + * @h: Node to be checked + * + * Not that not all removal functions will leave a node in unhashed state. + * For example, hlist_del_init_rcu() leaves the node in unhashed state, + * but hlist_nulls_del() does not. Unlike hlist_nulls_unhashed(), this + * function may be used locklessly. + */ +static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h) +{ + return !READ_ONCE(h->pprev); +} + static inline int hlist_nulls_empty(const struct hlist_nulls_head *h) { return is_a_nulls(READ_ONCE(h->first));
| |