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SubjectRe: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points
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On 01/16/2017 11:13 AM, Junxiao Bi wrote:
> On 01/16/2017 11:06 AM, Eric Ren wrote:
>> Hi Junxiao,
>>
>> On 01/16/2017 10:46 AM, Junxiao Bi wrote:
>>>>> If had_lock==true, it is a bug? I think we should BUG_ON for it, that
>>>>> can help us catch bug at the first time.
>>>> Good idea! But I'm not sure if "ocfs2_setattr" is always the first one
>>>> who takes the cluster lock.
>>>> It's harder for me to name all the possible paths;-/
>>> The BUG_ON() can help catch the path where ocfs2_setattr is not the
>>> first one.
>> Yes, I understand. But, the problem is that the vfs entries calling
>> order is out of our control.
>> I don't want to place an assertion where I'm not 100% sure it's
>> absolutely right;-)
> If it is not the first one, is it another recursive locking bug? In this
> case, if you don't like BUG_ON(), you can dump the call trace and print
> some warning message.

Yes! I like this idea, will add it in next version, thanks!

Eric

>
> Thanks,
> Junxiao.
>> Thanks,
>> Eric
>>
>>> Thanks,
>>> Junxiao.
>>>
>>>>>> + if (had_lock)
>>>>>> + arg_flags = OCFS2_META_LOCK_GETBH;
>>>>>> + status = ocfs2_inode_lock_full(inode, &bh, 1, arg_flags);
>>>>>> if (status < 0) {
>>>>>> if (status != -ENOENT)
>>>>>> mlog_errno(status);
>>>>>> goto bail_unlock_rw;
>>>>>> }
>>>>>> - inode_locked = 1;
>>>>>> + if (!had_lock) {
>>>>>> + ocfs2_add_holder(lockres, &oh);
>>>>>> + inode_locked = 1;
>>>>>> + }
>>>>>> if (size_change) {
>>>>>> status = inode_newsize_ok(inode, attr->ia_size);
>>>>>> @@ -1260,7 +1270,8 @@ int ocfs2_setattr(struct dentry *dentry, struct
>>>>>> iattr *attr)
>>>>>> bail_commit:
>>>>>> ocfs2_commit_trans(osb, handle);
>>>>>> bail_unlock:
>>>>>> - if (status) {
>>>>>> + if (status && inode_locked) {
>>>>>> + ocfs2_remove_holder(lockres, &oh);
>>>>>> ocfs2_inode_unlock(inode, 1);
>>>>>> inode_locked = 0;
>>>>>> }
>>>>>> @@ -1278,8 +1289,10 @@ int ocfs2_setattr(struct dentry *dentry,
>>>>>> struct iattr *attr)
>>>>>> if (status < 0)
>>>>>> mlog_errno(status);
>>>>>> }
>>>>>> - if (inode_locked)
>>>>>> + if (inode_locked) {
>>>>>> + ocfs2_remove_holder(lockres, &oh);
>>>>>> ocfs2_inode_unlock(inode, 1);
>>>>>> + }
>>>>>> brelse(bh);
>>>>>> return status;
>>>>>> @@ -1321,20 +1334,31 @@ int ocfs2_getattr(struct vfsmount *mnt,
>>>>>> int ocfs2_permission(struct inode *inode, int mask)
>>>>>> {
>>>>>> int ret;
>>>>>> + int has_locked;
>>>>>> + struct ocfs2_holder oh;
>>>>>> + struct ocfs2_lock_res *lockres;
>>>>>> if (mask & MAY_NOT_BLOCK)
>>>>>> return -ECHILD;
>>>>>> - ret = ocfs2_inode_lock(inode, NULL, 0);
>>>>>> - if (ret) {
>>>>>> - if (ret != -ENOENT)
>>>>>> - mlog_errno(ret);
>>>>>> - goto out;
>>>>>> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
>>>>>> + has_locked = (ocfs2_is_locked_by_me(lockres) != NULL);
>>>>> The same thing as ocfs2_setattr.
>>>> OK. I will think over your suggestions!
>>>>
>>>> Thanks,
>>>> Eric
>>>>
>>>>> Thanks,
>>>>> Junxiao.
>>>>>> + if (!has_locked) {
>>>>>> + ret = ocfs2_inode_lock(inode, NULL, 0);
>>>>>> + if (ret) {
>>>>>> + if (ret != -ENOENT)
>>>>>> + mlog_errno(ret);
>>>>>> + goto out;
>>>>>> + }
>>>>>> + ocfs2_add_holder(lockres, &oh);
>>>>>> }
>>>>>> ret = generic_permission(inode, mask);
>>>>>> - ocfs2_inode_unlock(inode, 0);
>>>>>> + if (!has_locked) {
>>>>>> + ocfs2_remove_holder(lockres, &oh);
>>>>>> + ocfs2_inode_unlock(inode, 0);
>>>>>> + }
>>>>>> out:
>>>>>> return ret;
>>>>>> }
>>>>>>
>

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