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authorDaniel Wagner <daniel.wagner@bmw-carit.de>2016-02-19 09:46:40 +0100
committerThomas Gleixner <tglx@linutronix.de>2016-02-25 11:27:16 +0100
commit065bb78c5b09df54d1c32e03227deb777ddff57b (patch)
treefafc2602468973386af7bd1c52b7d789b47ae000 /kernel/rcu/tree_plugin.h
parent8577370fb0cbe88266b7583d8d3b9f43ced077a0 (diff)
downloadlinux-sh-065bb78c5b09df54d1c32e03227deb777ddff57b.tar.gz
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: [<ffffffff811387c7>] rcu_gp_kthread+0xb97/0xeb0 {IN-SOFTIRQ-W} state was registered at: [<ffffffff81109b9f>] __lock_acquire+0xd5f/0x21e0 [<ffffffff8110be0f>] lock_acquire+0xdf/0x2b0 [<ffffffff81841cc9>] _raw_spin_lock_irqsave+0x59/0xa0 [<ffffffff81136991>] rcu_process_callbacks+0x141/0x3c0 [<ffffffff810b1a9d>] __do_softirq+0x14d/0x670 [<ffffffff810b2214>] irq_exit+0x104/0x110 [<ffffffff81844e96>] smp_apic_timer_interrupt+0x46/0x60 [<ffffffff81842e70>] apic_timer_interrupt+0x70/0x80 [<ffffffff810dba66>] rq_attach_root+0xa6/0x100 [<ffffffff810dbc2d>] cpu_attach_domain+0x16d/0x650 [<ffffffff810e4b42>] build_sched_domains+0x942/0xb00 [<ffffffff821777c2>] sched_init_smp+0x509/0x5c1 [<ffffffff821551e3>] kernel_init_freeable+0x172/0x28f [<ffffffff8182cdce>] kernel_init+0xe/0xe0 [<ffffffff8184231f>] ret_from_fork+0x3f/0x70 irq event stamp: 76 hardirqs last enabled at (75): [<ffffffff81841330>] _raw_spin_unlock_irq+0x30/0x60 hardirqs last disabled at (76): [<ffffffff8184116f>] _raw_spin_lock_irq+0x1f/0x90 softirqs last enabled at (0): [<ffffffff810a8df2>] 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); <Interrupt> lock(rcu_node_1); *** DEADLOCK *** 1 lock held by rcu_preempt/8: #0: (rcu_node_1){+.?...}, at: [<ffffffff811387c7>] 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: [<ffffffff818379e0>] dump_stack+0x4f/0x7b [<ffffffff8110813b>] print_usage_bug+0x1db/0x1e0 [<ffffffff8102fa4f>] ? save_stack_trace+0x2f/0x50 [<ffffffff811087ad>] mark_lock+0x66d/0x6e0 [<ffffffff81107790>] ? check_usage_forwards+0x150/0x150 [<ffffffff81108898>] mark_held_locks+0x78/0xa0 [<ffffffff81841330>] ? _raw_spin_unlock_irq+0x30/0x60 [<ffffffff81108a28>] trace_hardirqs_on_caller+0x168/0x220 [<ffffffff81108aed>] trace_hardirqs_on+0xd/0x10 [<ffffffff81841330>] _raw_spin_unlock_irq+0x30/0x60 [<ffffffff810fd1c7>] swake_up_all+0xb7/0xe0 [<ffffffff811386e1>] rcu_gp_kthread+0xab1/0xeb0 [<ffffffff811089bf>] ? trace_hardirqs_on_caller+0xff/0x220 [<ffffffff81841341>] ? _raw_spin_unlock_irq+0x41/0x60 [<ffffffff81137c30>] ? rcu_barrier+0x20/0x20 [<ffffffff810d2014>] kthread+0x104/0x120 [<ffffffff81841330>] ? _raw_spin_unlock_irq+0x30/0x60 [<ffffffff810d1f10>] ? kthread_create_on_node+0x260/0x260 [<ffffffff8184231f>] ret_from_fork+0x3f/0x70 [<ffffffff810d1f10>] ? kthread_create_on_node+0x260/0x260 Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-5-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
-rw-r--r--kernel/rcu/tree_plugin.h16
1 files changed, 13 insertions, 3 deletions
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)
{
}