blob: 9d581ea7473ee35b8c0f475835c0e8db59852f32 [file] [log] [blame]
From 911838b34146ab5c4fceee40844e1c785ef88253 Mon Sep 17 00:00:00 2001
From: Marco Elver <elver@google.com>
Date: Wed, 9 Oct 2019 17:57:43 +0200
Subject: [PATCH] rcu: Fix data-race due to atomic_t copy-by-value
commit 6cf539a87a61a4fbc43f625267dbcbcf283872ed upstream.
This fixes a data-race where `atomic_t dynticks` is copied by value. The
copy is performed non-atomically, resulting in a data-race if `dynticks`
is updated concurrently.
This data-race was found with KCSAN:
==================================================================
BUG: KCSAN: data-race in dyntick_save_progress_counter / rcu_irq_enter
write to 0xffff989dbdbe98e0 of 4 bytes by task 10 on cpu 3:
atomic_add_return include/asm-generic/atomic-instrumented.h:78 [inline]
rcu_dynticks_snap kernel/rcu/tree.c:310 [inline]
dyntick_save_progress_counter+0x43/0x1b0 kernel/rcu/tree.c:984
force_qs_rnp+0x183/0x200 kernel/rcu/tree.c:2286
rcu_gp_fqs kernel/rcu/tree.c:1601 [inline]
rcu_gp_fqs_loop+0x71/0x880 kernel/rcu/tree.c:1653
rcu_gp_kthread+0x22c/0x3b0 kernel/rcu/tree.c:1799
kthread+0x1b5/0x200 kernel/kthread.c:255
<snip>
read to 0xffff989dbdbe98e0 of 4 bytes by task 154 on cpu 7:
rcu_nmi_enter_common kernel/rcu/tree.c:828 [inline]
rcu_irq_enter+0xda/0x240 kernel/rcu/tree.c:870
irq_enter+0x5/0x50 kernel/softirq.c:347
<snip>
Reported by Kernel Concurrency Sanitizer on:
CPU: 7 PID: 154 Comm: kworker/7:1H Not tainted 5.3.0+ #5
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
Workqueue: kblockd blk_mq_run_work_fn
==================================================================
Signed-off-by: Marco Elver <elver@google.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 02a3f78f7cd8..cea2d45e6aad 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -442,7 +442,7 @@ TRACE_EVENT_RCU(rcu_fqs,
*/
TRACE_EVENT_RCU(rcu_dyntick,
- TP_PROTO(const char *polarity, long oldnesting, long newnesting, atomic_t dynticks),
+ TP_PROTO(const char *polarity, long oldnesting, long newnesting, int dynticks),
TP_ARGS(polarity, oldnesting, newnesting, dynticks),
@@ -457,7 +457,7 @@ TRACE_EVENT_RCU(rcu_dyntick,
__entry->polarity = polarity;
__entry->oldnesting = oldnesting;
__entry->newnesting = newnesting;
- __entry->dynticks = atomic_read(&dynticks);
+ __entry->dynticks = dynticks;
),
TP_printk("%s %lx %lx %#3x", __entry->polarity,
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index affa7aae758f..58cdad75ddac 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -547,7 +547,7 @@ static void rcu_eqs_enter(bool user)
}
lockdep_assert_irqs_disabled();
- trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, rdp->dynticks);
+ trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks));
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
rdp = this_cpu_ptr(&rcu_data);
do_nocb_deferred_wakeup(rdp);
@@ -620,14 +620,15 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
* leave it in non-RCU-idle state.
*/
if (rdp->dynticks_nmi_nesting != 1) {
- trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
+ trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
+ atomic_read(&rdp->dynticks));
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
rdp->dynticks_nmi_nesting - 2);
return;
}
/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
- trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, rdp->dynticks);
+ trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
if (irq)
@@ -714,7 +715,7 @@ static void rcu_eqs_exit(bool user)
rcu_dynticks_task_exit();
rcu_dynticks_eqs_exit();
rcu_cleanup_after_idle();
- trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, rdp->dynticks);
+ trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks));
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
WRITE_ONCE(rdp->dynticks_nesting, 1);
WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
@@ -798,7 +799,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
}
trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
rdp->dynticks_nmi_nesting,
- rdp->dynticks_nmi_nesting + incby, rdp->dynticks);
+ rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
rdp->dynticks_nmi_nesting + incby);
barrier();
--
2.7.4