| From 966d2b04e070bc040319aaebfec09e0144dc3341 Mon Sep 17 00:00:00 2001 |
| From: Douglas Miller <dougmill@linux.vnet.ibm.com> |
| Date: Sat, 28 Jan 2017 06:42:20 -0600 |
| Subject: percpu-refcount: fix reference leak during percpu-atomic transition |
| |
| From: Douglas Miller <dougmill@linux.vnet.ibm.com> |
| |
| commit 966d2b04e070bc040319aaebfec09e0144dc3341 upstream. |
| |
| percpu_ref_tryget() and percpu_ref_tryget_live() should return |
| "true" IFF they acquire a reference. But the return value from |
| atomic_long_inc_not_zero() is a long and may have high bits set, |
| e.g. PERCPU_COUNT_BIAS, and the return value of the tryget routines |
| is bool so the reference may actually be acquired but the routines |
| return "false" which results in a reference leak since the caller |
| assumes it does not need to do a corresponding percpu_ref_put(). |
| |
| This was seen when performing CPU hotplug during I/O, as hangs in |
| blk_mq_freeze_queue_wait where percpu_ref_kill (blk_mq_freeze_queue_start) |
| raced with percpu_ref_tryget (blk_mq_timeout_work). |
| Sample stack trace: |
| |
| __switch_to+0x2c0/0x450 |
| __schedule+0x2f8/0x970 |
| schedule+0x48/0xc0 |
| blk_mq_freeze_queue_wait+0x94/0x120 |
| blk_mq_queue_reinit_work+0xb8/0x180 |
| blk_mq_queue_reinit_prepare+0x84/0xa0 |
| cpuhp_invoke_callback+0x17c/0x600 |
| cpuhp_up_callbacks+0x58/0x150 |
| _cpu_up+0xf0/0x1c0 |
| do_cpu_up+0x120/0x150 |
| cpu_subsys_online+0x64/0xe0 |
| device_online+0xb4/0x120 |
| online_store+0xb4/0xc0 |
| dev_attr_store+0x68/0xa0 |
| sysfs_kf_write+0x80/0xb0 |
| kernfs_fop_write+0x17c/0x250 |
| __vfs_write+0x6c/0x1e0 |
| vfs_write+0xd0/0x270 |
| SyS_write+0x6c/0x110 |
| system_call+0x38/0xe0 |
| |
| Examination of the queue showed a single reference (no PERCPU_COUNT_BIAS, |
| and __PERCPU_REF_DEAD, __PERCPU_REF_ATOMIC set) and no requests. |
| However, conditions at the time of the race are count of PERCPU_COUNT_BIAS + 0 |
| and __PERCPU_REF_DEAD and __PERCPU_REF_ATOMIC set. |
| |
| The fix is to make the tryget routines use an actual boolean internally instead |
| of the atomic long result truncated to a int. |
| |
| Fixes: e625305b3907 percpu-refcount: make percpu_ref based on longs instead of ints |
| Link: https://bugzilla.kernel.org/show_bug.cgi?id=190751 |
| Signed-off-by: Douglas Miller <dougmill@linux.vnet.ibm.com> |
| Reviewed-by: Jens Axboe <axboe@fb.com> |
| Signed-off-by: Tejun Heo <tj@kernel.org> |
| Fixes: e625305b3907 ("percpu-refcount: make percpu_ref based on longs instead of ints") |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| include/linux/percpu-refcount.h | 4 ++-- |
| 1 file changed, 2 insertions(+), 2 deletions(-) |
| |
| --- a/include/linux/percpu-refcount.h |
| +++ b/include/linux/percpu-refcount.h |
| @@ -204,7 +204,7 @@ static inline void percpu_ref_get(struct |
| static inline bool percpu_ref_tryget(struct percpu_ref *ref) |
| { |
| unsigned long __percpu *percpu_count; |
| - int ret; |
| + bool ret; |
| |
| rcu_read_lock_sched(); |
| |
| @@ -238,7 +238,7 @@ static inline bool percpu_ref_tryget(str |
| static inline bool percpu_ref_tryget_live(struct percpu_ref *ref) |
| { |
| unsigned long __percpu *percpu_count; |
| - int ret = false; |
| + bool ret = false; |
| |
| rcu_read_lock_sched(); |
| |