[Ocfs2-devel] [PATCH v2] ocfs2/cluster: unlock the o2hb_live_lock before the o2nm_depend_item()
alex chen
alex.chen at huawei.com
Mon Nov 6 18:30:03 PST 2017
Hi Joseph,
Thanks for your reply.
For the global heartbeat mode, the concurrently access to reg->hr_item_pinned
may be happened after unlocking. I will modify this patch and send the patch v3.
Thanks,
Alex
On 2017/11/6 17:37, Joseph Qi wrote:
> Hi Alex,
>
> For local heartbeat mode, I understand that if the region is not found,
> o2hb_live_lock won't be released. And if the region is found, it doesn't
> have to iterate the next region. So I agree with your fix in this case.
>
> But I still don't get how to make sure the safe iteration in case of
> global heartbeat mode.
>
> Thanks,
> Joseph
>
> On 17/11/2 14:00, 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.
>>
>> 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 | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
>> index d020604..07b2fdc 100644
>> --- a/fs/ocfs2/cluster/heartbeat.c
>> +++ b/fs/ocfs2/cluster/heartbeat.c
>> @@ -2399,8 +2399,15 @@ 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);
>> +
>> /* Ignore ENOENT only for local hb (userdlm domain) */
>> ret = o2nm_depend_item(®->hr_item);
>> +
>> + config_item_put(®->hr_item);
>> + spin_lock(&o2hb_live_lock);
>> +
>> if (!ret) {
>> mlog(ML_CLUSTER, "Pin region %s\n", uuid);
>> reg->hr_item_pinned = 1;
>>
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