From: Marco Elver elver@google.com
[ Upstream commit 6cf539a87a61a4fbc43f625267dbcbcf283872ed ]
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: Sasha Levin sashal@kernel.org --- include/trace/events/rcu.h | 4 ++-- kernel/rcu/tree.c | 11 ++++++----- 2 files changed, 8 insertions(+), 7 deletions(-)
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index 66122602bd085..697e2c0624dcd 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -449,7 +449,7 @@ 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),
@@ -464,7 +464,7 @@ 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 1694a6b57ad8c..6145e08a14072 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -577,7 +577,7 @@ 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); @@ -650,14 +650,15 @@ 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) @@ -744,7 +745,7 @@ 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); @@ -833,7 +834,7 @@ 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();