[Ocfs2-devel] [PATCH] ocfs2/cluster: unlock the o2hb_live_lock before the o2nm_depend_item()
Changwei Ge
ge.changwei at h3c.com
Tue Oct 31 18:14:08 PDT 2017
On 2017/11/1 9:05, Joseph Qi wrote:
> Hi Alex,
>
> On 17/10/31 20:41, alex chen wrote:
>> In the following situation, the down_write() will be called under
>> the spin_lock(), which may lead a soft lockup:
>> o2hb_region_inc_user
>> spin_lock(&o2hb_live_lock)
>> o2hb_region_pin
>> o2nm_depend_item
>> configfs_depend_item
>> inode_lock
>> down_write
>> -->here may sleep and reschedule
>>
>> So we should unlock the o2hb_live_lock before the o2nm_depend_item(), and
>> get item reference in advance to prevent the region to be released.
Hi Alex,
Actually, I don't figure why this code path will lead to a soft lockup
yet. Can you elaborate further?
And I agree with Joseph that simply unlocking o2hb_live_lock will
introduce a race here since we are waking through that global list.
Thanks,
Changwei
>>
>> Signed-off-by: Alex Chen <alex.chen at huawei.com>
>> Reviewed-by: Yiwen Jiang <jiangyiwen at huawei.com>
>> Reviewed-by: Jun Piao <piaojun at huawei.com>
>> ---
>> fs/ocfs2/cluster/heartbeat.c | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
>> index d020604..f1142a9 100644
>> --- a/fs/ocfs2/cluster/heartbeat.c
>> +++ b/fs/ocfs2/cluster/heartbeat.c
>> @@ -2399,6 +2399,9 @@ static int o2hb_region_pin(const char *region_uuid)
>> if (reg->hr_item_pinned || reg->hr_item_dropped)
>> goto skip_pin;
>>
>> + config_item_get(®->hr_item);
>> + spin_unlock(&o2hb_live_lock);
>> +
> If unlock here, the iteration of o2hb_all_regions is no longer safe.
>
> Thanks,
> Joseph
>
>> /* Ignore ENOENT only for local hb (userdlm domain) */
>> ret = o2nm_depend_item(®->hr_item);
>> if (!ret) {
>> @@ -2410,9 +2413,14 @@ static int o2hb_region_pin(const char *region_uuid)
>> else {
>> mlog(ML_ERROR, "Pin region %s fails with %d\n",
>> uuid, ret);
>> + config_item_put(®->hr_item);
>> + spin_lock(&o2hb_live_lock);
>> break;
>> }
>> }
>> +
>> + config_item_put(®->hr_item);
>> + spin_lock(&o2hb_live_lock);
>> skip_pin:
>> if (found)
>> break;
>> -- 1.9.5.msysgit.1
>>
>>
>
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