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| author |   Dmitry Vyukov <dvyukov@google.com> | 2017-03-05 12:17:31 -0800 |
|---|---|---|
| committer |   Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-04-18 11:38:19 -0700 |
| commit | f010ed82c7ba8b30f30872800100ad6b6efe2a6a (patch) | |
| tree | 364a4b0d21554bf43408fcfd8d147fb29ff69140 | |
| parent | rcu: Expedited wakeups need to be fully ordered (diff) | |
| download | linux-dev-f010ed82c7ba8b30f30872800100ad6b6efe2a6a.tar.xz linux-dev-f010ed82c7ba8b30f30872800100ad6b6efe2a6a.zip | |
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
---
| -rw-r--r-- | kernel/rcu/rcu.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 91e0bf31f6ce..0bc1313c49e2 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. */ |