From 065bb78c5b09df54d1c32e03227deb777ddff57b Mon Sep 17 00:00:00 2001 From: Daniel Wagner Date: Fri, 19 Feb 2016 09:46:40 +0100 Subject: [PATCH] rcu: Do not call rcu_nocb_gp_cleanup() while holding rnp->lock rcu_nocb_gp_cleanup() is called while holding rnp->lock. Currently, this is okay because the wake_up_all() in rcu_nocb_gp_cleanup() will not enable the IRQs. lockdep is happy. By switching over using swait this is not true anymore. swake_up_all() enables the IRQs while processing the waiters. __do_softirq() can now run and will eventually call rcu_process_callbacks() which wants to grap nrp->lock. Let's move the rcu_nocb_gp_cleanup() call outside the lock before we switch over to swait. If we would hold the rnp->lock and use swait, lockdep reports following: ================================= [ INFO: inconsistent lock state ] 4.2.0-rc5-00025-g9a73ba0 #136 Not tainted --------------------------------- inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage. rcu_preempt/8 [HC0[0]:SC0[0]:HE1:SE1] takes: (rcu_node_1){+.?...}, at: [] rcu_gp_kthread+0xb97/0xeb0 {IN-SOFTIRQ-W} state was registered at: [] __lock_acquire+0xd5f/0x21e0 [] lock_acquire+0xdf/0x2b0 [] _raw_spin_lock_irqsave+0x59/0xa0 [] rcu_process_callbacks+0x141/0x3c0 [] __do_softirq+0x14d/0x670 [] irq_exit+0x104/0x110 [] smp_apic_timer_interrupt+0x46/0x60 [] apic_timer_interrupt+0x70/0x80 [] rq_attach_root+0xa6/0x100 [] cpu_attach_domain+0x16d/0x650 [] build_sched_domains+0x942/0xb00 [] sched_init_smp+0x509/0x5c1 [] kernel_init_freeable+0x172/0x28f [] kernel_init+0xe/0xe0 [] ret_from_fork+0x3f/0x70 irq event stamp: 76 hardirqs last enabled at (75): [] _raw_spin_unlock_irq+0x30/0x60 hardirqs last disabled at (76): [] _raw_spin_lock_irq+0x1f/0x90 softirqs last enabled at (0): [] copy_process.part.26+0x602/0x1cf0 softirqs last disabled at (0): [< (null)>] (null) other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(rcu_node_1); lock(rcu_node_1); *** DEADLOCK *** 1 lock held by rcu_preempt/8: #0: (rcu_node_1){+.?...}, at: [] rcu_gp_kthread+0xb97/0xeb0 stack backtrace: CPU: 0 PID: 8 Comm: rcu_preempt Not tainted 4.2.0-rc5-00025-g9a73ba0 #136 Hardware name: Dell Inc. PowerEdge R820/066N7P, BIOS 2.0.20 01/16/2014 0000000000000000 000000006d7e67d8 ffff881fb081fbd8 ffffffff818379e0 0000000000000000 ffff881fb0812a00 ffff881fb081fc38 ffffffff8110813b 0000000000000000 0000000000000001 ffff881f00000001 ffffffff8102fa4f Call Trace: [] dump_stack+0x4f/0x7b [] print_usage_bug+0x1db/0x1e0 [] ? save_stack_trace+0x2f/0x50 [] mark_lock+0x66d/0x6e0 [] ? check_usage_forwards+0x150/0x150 [] mark_held_locks+0x78/0xa0 [] ? _raw_spin_unlock_irq+0x30/0x60 [] trace_hardirqs_on_caller+0x168/0x220 [] trace_hardirqs_on+0xd/0x10 [] _raw_spin_unlock_irq+0x30/0x60 [] swake_up_all+0xb7/0xe0 [] rcu_gp_kthread+0xab1/0xeb0 [] ? trace_hardirqs_on_caller+0xff/0x220 [] ? _raw_spin_unlock_irq+0x41/0x60 [] ? rcu_barrier+0x20/0x20 [] kthread+0x104/0x120 [] ? _raw_spin_unlock_irq+0x30/0x60 [] ? kthread_create_on_node+0x260/0x260 [] ret_from_fork+0x3f/0x70 [] ? kthread_create_on_node+0x260/0x260 Signed-off-by: Daniel Wagner Acked-by: Peter Zijlstra (Intel) Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng Cc: Marcelo Tosatti Cc: Steven Rostedt Cc: Paul Gortmaker Cc: Paolo Bonzini Cc: "Paul E. McKenney" Link: http://lkml.kernel.org/r/1455871601-27484-5-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner --- kernel/rcu/tree.c | 4 +++- kernel/rcu/tree.h | 3 ++- kernel/rcu/tree_plugin.h | 16 +++++++++++++--- 3 files changed, 18 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e41dd4131f7a..8e8c6ec1d30f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1614,7 +1614,6 @@ static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) int needmore; struct rcu_data *rdp = this_cpu_ptr(rsp->rda); - rcu_nocb_gp_cleanup(rsp, rnp); rnp->need_future_gp[c & 0x1] = 0; needmore = rnp->need_future_gp[(c + 1) & 0x1]; trace_rcu_future_gp(rnp, rdp, c, @@ -2010,6 +2009,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) int nocb = 0; struct rcu_data *rdp; struct rcu_node *rnp = rcu_get_root(rsp); + wait_queue_head_t *sq; WRITE_ONCE(rsp->gp_activity, jiffies); raw_spin_lock_irq_rcu_node(rnp); @@ -2046,7 +2046,9 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) needgp = __note_gp_changes(rsp, rnp, rdp) || needgp; /* smp_mb() provided by prior unlock-lock pair. */ nocb += rcu_future_gp_cleanup(rsp, rnp); + sq = rcu_nocb_gp_get(rnp); raw_spin_unlock_irq(&rnp->lock); + rcu_nocb_gp_cleanup(sq); cond_resched_rcu_qs(); WRITE_ONCE(rsp->gp_activity, jiffies); rcu_gp_slow(rsp, gp_cleanup_delay); diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 83360b4f4352..10dedfbef09d 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -621,7 +621,8 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp); static void increment_cpu_stall_ticks(void); static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu); static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq); -static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp); +static wait_queue_head_t *rcu_nocb_gp_get(struct rcu_node *rnp); +static void rcu_nocb_gp_cleanup(wait_queue_head_t *sq); static void rcu_init_one_nocb(struct rcu_node *rnp); static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, bool lazy, unsigned long flags); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 9467a8b7e756..631aff61abe9 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1811,9 +1811,9 @@ early_param("rcu_nocb_poll", parse_rcu_nocb_poll); * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended * grace period. */ -static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) +static void rcu_nocb_gp_cleanup(wait_queue_head_t *sq) { - wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); + wake_up_all(sq); } /* @@ -1829,6 +1829,11 @@ static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; } +static wait_queue_head_t *rcu_nocb_gp_get(struct rcu_node *rnp) +{ + return &rnp->nocb_gp_wq[rnp->completed & 0x1]; +} + static void rcu_init_one_nocb(struct rcu_node *rnp) { init_waitqueue_head(&rnp->nocb_gp_wq[0]); @@ -2502,7 +2507,7 @@ static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) return false; } -static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) +static void rcu_nocb_gp_cleanup(wait_queue_head_t *sq) { } @@ -2510,6 +2515,11 @@ static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) { } +static wait_queue_head_t *rcu_nocb_gp_get(struct rcu_node *rnp) +{ + return NULL; +} + static void rcu_init_one_nocb(struct rcu_node *rnp) { } -- 2.20.1