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

[Eric Ren <zren@suse.com>]

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?

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;
>>>>   }
>>>
>>>
>>
>
>