Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points

[Joseph Qi <jiangqi903@gmail.com>]

On 17/1/6 16:21, Eric Ren wrote:
> On 01/06/2017 03:14 PM, Joseph Qi wrote:
>>
>>
>> On 17/1/6 14:56, Eric Ren wrote:
>>> On 01/06/2017 02:09 PM, Joseph Qi wrote:
>>>> Hi Eric,
>>>>
>>>>
>>>> On 17/1/5 23:31, Eric Ren wrote:
>>>>> Commit 743b5f1434f5 ("ocfs2: take inode lock in 
>>>>> ocfs2_iop_set/get_acl()")
>>>>> results in a deadlock, as the author "Tariq Saeed" realized shortly
>>>>> after the patch was merged. The discussion happened here
>>>>> (https://oss.oracle.com/pipermail/ocfs2-devel/2015-September/011085.html). 
>>>>>
>>>>>
>>>>> The reason why taking cluster inode lock at vfs entry points opens up
>>>>> a self deadlock window, is explained in the previous patch of this
>>>>> series.
>>>>>
>>>>> So far, we have seen two different code paths that have this issue.
>>>>> 1. do_sys_open
>>>>>       may_open
>>>>>        inode_permission
>>>>>         ocfs2_permission
>>>>>          ocfs2_inode_lock() <=== take PR
>>>>>           generic_permission
>>>>>            get_acl
>>>>>             ocfs2_iop_get_acl
>>>>>              ocfs2_inode_lock() <=== take PR
>>>>> 2. fchmod|fchmodat
>>>>>      chmod_common
>>>>>       notify_change
>>>>>        ocfs2_setattr <=== take EX
>>>>>         posix_acl_chmod
>>>>>          get_acl
>>>>>           ocfs2_iop_get_acl <=== take PR
>>>>>          ocfs2_iop_set_acl <=== take EX
>>>>>
>>>>> Fixes them by adding the tracking logic (in the previous patch) for
>>>>> these funcs above, ocfs2_permission(), ocfs2_iop_[set|get]_acl(),
>>>>> ocfs2_setattr().
>>>> As described cases above, shall we just add the tracking logic only 
>>>> for set/get_acl()?
>>>
>>> The idea is to detect recursive locking on the running task stack. 
>>> Take case 1) for example if ocfs2_permisssion()
>>> is not changed:
>>>
>>> ocfs2_permission() <=== take PR, ocfs2_holder is not added
>>>    ocfs2_iop_get_acl <=== still take PR, because there is no lock 
>>> holder on the tracking list
>> I mean we have no need to check if locked by me, just do inode lock 
>> and add holder.
>> This will make code more clean, IMO.
> Oh, sorry, I get your point this time. I think we need to check it if 
> there are more than one processes that hold
> PR lock on the same resource.  If I don't understand you correctly, 
> please tell me why you think it's not neccessary
> to check before getting lock?
The code logic can only check if it is locked by myself. In the case
described above, ocfs2_permission is the first entry to take inode lock.
And even if check succeeds, it is a bug without unlock, but not the case
of recursive lock.

Thanks,
Joseph
>
> Thanks,
> Eric
>>
>> Thanks,
>> Joseph
>>>
>>> Thanks for your review;-)
>>> Eric
>>>
>>>>
>>>> Thanks,
>>>> Joseph
>>>>>
>>>>> Signed-off-by: Eric Ren <zren@suse.com>
>>>>> ---
>>>>>   fs/ocfs2/acl.c  | 39 ++++++++++++++++++++++++++++++++++-----
>>>>>   fs/ocfs2/file.c | 44 ++++++++++++++++++++++++++++++++++----------
>>>>>   2 files changed, 68 insertions(+), 15 deletions(-)
>>>>>
>>>>> diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
>>>>> index bed1fcb..c539890 100644
>>>>> --- a/fs/ocfs2/acl.c
>>>>> +++ b/fs/ocfs2/acl.c
>>>>> @@ -284,16 +284,31 @@ int ocfs2_iop_set_acl(struct inode *inode, 
>>>>> struct posix_acl *acl, int type)
>>>>>   {
>>>>>       struct buffer_head *bh = NULL;
>>>>>       int status = 0;
>>>>> -
>>>>> -    status = ocfs2_inode_lock(inode, &bh, 1);
>>>>> +    int arg_flags = 0, has_locked;
>>>>> +    struct ocfs2_holder oh;
>>>>> +    struct ocfs2_lock_res *lockres;
>>>>> +
>>>>> +    lockres = &OCFS2_I(inode)->ip_inode_lockres;
>>>>> +    has_locked = (ocfs2_is_locked_by_me(lockres) != NULL);
>>>>> +    if (has_locked)
>>>>> +        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);
>>>>>           return status;
>>>>>       }
>>>>> +    if (!has_locked)
>>>>> +        ocfs2_add_holder(lockres, &oh);
>>>>> +
>>>>>       status = ocfs2_set_acl(NULL, inode, bh, type, acl, NULL, NULL);
>>>>> -    ocfs2_inode_unlock(inode, 1);
>>>>> +
>>>>> +    if (!has_locked) {
>>>>> +        ocfs2_remove_holder(lockres, &oh);
>>>>> +        ocfs2_inode_unlock(inode, 1);
>>>>> +    }
>>>>>       brelse(bh);
>>>>> +
>>>>>       return status;
>>>>>   }
>>>>>   @@ -303,21 +318,35 @@ struct posix_acl *ocfs2_iop_get_acl(struct 
>>>>> inode *inode, int type)
>>>>>       struct buffer_head *di_bh = NULL;
>>>>>       struct posix_acl *acl;
>>>>>       int ret;
>>>>> +    int arg_flags = 0, has_locked;
>>>>> +    struct ocfs2_holder oh;
>>>>> +    struct ocfs2_lock_res *lockres;
>>>>>         osb = OCFS2_SB(inode->i_sb);
>>>>>       if (!(osb->s_mount_opt & OCFS2_MOUNT_POSIX_ACL))
>>>>>           return NULL;
>>>>> -    ret = ocfs2_inode_lock(inode, &di_bh, 0);
>>>>> +
>>>>> +    lockres = &OCFS2_I(inode)->ip_inode_lockres;
>>>>> +    has_locked = (ocfs2_is_locked_by_me(lockres) != NULL);
>>>>> +    if (has_locked)
>>>>> +        arg_flags = OCFS2_META_LOCK_GETBH;
>>>>> +    ret = ocfs2_inode_lock_full(inode, &di_bh, 0, arg_flags);
>>>>>       if (ret < 0) {
>>>>>           if (ret != -ENOENT)
>>>>>               mlog_errno(ret);
>>>>>           return ERR_PTR(ret);
>>>>>       }
>>>>> +    if (!has_locked)
>>>>> +        ocfs2_add_holder(lockres, &oh);
>>>>>         acl = ocfs2_get_acl_nolock(inode, type, di_bh);
>>>>>   -    ocfs2_inode_unlock(inode, 0);
>>>>> +    if (!has_locked) {
>>>>> +        ocfs2_remove_holder(lockres, &oh);
>>>>> +        ocfs2_inode_unlock(inode, 0);
>>>>> +    }
>>>>>       brelse(di_bh);
>>>>> +
>>>>>       return acl;
>>>>>   }
>>>>>   diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
>>>>> index c488965..62be75d 100644
>>>>> --- a/fs/ocfs2/file.c
>>>>> +++ b/fs/ocfs2/file.c
>>>>> @@ -1138,6 +1138,9 @@ int ocfs2_setattr(struct dentry *dentry, 
>>>>> struct iattr *attr)
>>>>>       handle_t *handle = NULL;
>>>>>       struct dquot *transfer_to[MAXQUOTAS] = { };
>>>>>       int qtype;
>>>>> +    int arg_flags = 0, had_lock;
>>>>> +    struct ocfs2_holder oh;
>>>>> +    struct ocfs2_lock_res *lockres;
>>>>>         trace_ocfs2_setattr(inode, dentry,
>>>>>                   (unsigned long long)OCFS2_I(inode)->ip_blkno,
>>>>> @@ -1173,13 +1176,20 @@ int ocfs2_setattr(struct dentry *dentry, 
>>>>> struct iattr *attr)
>>>>>           }
>>>>>       }
>>>>>   -    status = ocfs2_inode_lock(inode, &bh, 1);
>>>>> +    lockres = &OCFS2_I(inode)->ip_inode_lockres;
>>>>> +    had_lock = (ocfs2_is_locked_by_me(lockres) != NULL);
>>>>> +    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);
>>>>> +    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;
>>>>>   }
>>>>
>>>>
>>>
>>
>>
>