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authorDmitry Vyukov <dvyukov@google.com>2017-03-05 12:17:31 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-18 11:38:19 -0700
commitf010ed82c7ba8b30f30872800100ad6b6efe2a6a (patch)
tree364a4b0d21554bf43408fcfd8d147fb29ff69140 /kernel
parent3c345825c899df0751b01143b159ddaefb91a220 (diff)
downloadop-kernel-dev-f010ed82c7ba8b30f30872800100ad6b6efe2a6a.zip
op-kernel-dev-f010ed82c7ba8b30f30872800100ad6b6efe2a6a.tar.gz
rcu: Fix warning in rcu_seq_end()
The rcu_seq_end() function increments seq signifying completion of a grace period, after that checks that the seq is even and wakes _synchronize_rcu_expedited(). The _synchronize_rcu_expedited() function uses wait_event() to wait for even seq. The problem is that wait_event() can return as soon as seq becomes even without waiting for the wakeup. In such case the warning in rcu_seq_end() can falsely fire if the next expedited grace period starts before the check. Check that seq has good value before incrementing it. Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Cc: syzkaller@googlegroups.com Cc: linux-kernel@vger.kernel.org Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: josh@joshtriplett.org Cc: jiangshanlai@gmail.com Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- syzkaller-triggered warning: WARNING: CPU: 0 PID: 4832 at kernel/rcu/tree.c:3533 rcu_seq_end+0x110/0x140 kernel/rcu/tree.c:3533 CPU: 0 PID: 4832 Comm: kworker/0:3 Not tainted 4.10.0+ #276 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Workqueue: events wait_rcu_exp_gp Call Trace: __dump_stack lib/dump_stack.c:15 [inline] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51 panic+0x1fb/0x412 kernel/panic.c:179 __warn+0x1c4/0x1e0 kernel/panic.c:540 warn_slowpath_null+0x2c/0x40 kernel/panic.c:583 rcu_seq_end+0x110/0x140 kernel/rcu/tree.c:3533 rcu_exp_gp_seq_end kernel/rcu/tree_exp.h:36 [inline] rcu_exp_wait_wake+0x8a9/0x1330 kernel/rcu/tree_exp.h:517 rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:559 [inline] wait_rcu_exp_gp+0x83/0xc0 kernel/rcu/tree_exp.h:570 process_one_work+0xc06/0x1c20 kernel/workqueue.c:2096 worker_thread+0x223/0x19c0 kernel/workqueue.c:2230 kthread+0x326/0x3f0 kernel/kthread.c:227 ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430 ---
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu/rcu.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 91e0bf3..0bc1313 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -73,8 +73,8 @@ static inline void rcu_seq_start(unsigned long *sp)
static inline void rcu_seq_end(unsigned long *sp)
{
smp_mb(); /* Ensure update-side operation before counter increment. */
+ WARN_ON_ONCE(!(*sp & 0x1));
WRITE_ONCE(*sp, *sp + 1);
- WARN_ON_ONCE(*sp & 0x1);
}
/* Take a snapshot of the update side's sequence number. */
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