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

From: Junxiao Bi <junxiao.bi@oracle.com>
To: Eric Ren <zren@suse.com>, ocfs2-devel@oss.oracle.com
Cc: akpm@linux-foundation.org, mfasheh@versity.com,
	jlbec@evilplan.org, ghe@suse.com, jiangqi903@gmail.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points
Date: Mon, 16 Jan 2017 10:46:11 +0800	[thread overview]
Message-ID: <6b3f4c7c-9276-321b-4e75-33c87a855757@oracle.com> (raw)
In-Reply-To: <31cc0413-6aa2-2493-fce6-f8f8ab9aaa16@suse.com>

On 01/13/2017 02:19 PM, Eric Ren wrote:
> Hi!
> 
> On 01/13/2017 12:22 PM, Junxiao Bi wrote:
>> On 01/05/2017 11:31 PM, 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().
>>>
>>> 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==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.

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;
>>>   }
>>>
>>
> 