Re: [PATCH v2 2/2] ocfs2: fix deadlock issue when taking inode lock at vfs entry points

[Junxiao Bi]

On 01/16/2017 02:42 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().
> 
> Changes since v1:
> 1. Let ocfs2_is_locked_by_me() just return true/false to indicate if the
> process gets the cluster lock - suggested by: Joseph Qi <jiangqi903@xxxxxxxxx>
> and Junxiao Bi <junxiao.bi@xxxxxxxxxx>.
> 
> 2. Change "struct ocfs2_holder" to a more meaningful name "ocfs2_lock_holder",
> suggested by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>.
> 
> 3. Add debugging output at ocfs2_setattr() and ocfs2_permission() to
> catch exceptional cases, suggested by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>.
> 
> Signed-off-by: Eric Ren <zren@xxxxxxxx>
> ---
>  fs/ocfs2/acl.c  | 39 +++++++++++++++++++++++++----
>  fs/ocfs2/file.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++--------
>  2 files changed, 100 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
> index bed1fcb..3e47262 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_lock_holder oh;
> +	struct ocfs2_lock_res *lockres;
> +
> +	lockres = &OCFS2_I(inode)->ip_inode_lockres;
> +	has_locked = ocfs2_is_locked_by_me(lockres);
> +	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);
> +
Same code pattern showed here and *get_acl, can it be abstracted to one
function?
The same issue for *setattr and *permission. Sorry for not mention that
in last review.

Thanks,
Junxiao.
>  	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_lock_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);
> +	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..b620c25 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_lock_holder oh;
> +	struct ocfs2_lock_res *lockres;
>  
>  	trace_ocfs2_setattr(inode, dentry,
>  			    (unsigned long long)OCFS2_I(inode)->ip_blkno,
> @@ -1173,13 +1176,41 @@ 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);
> +	if (had_lock) {
> +		arg_flags = OCFS2_META_LOCK_GETBH;
> +
> +		/*
> +		 * As far as we know, ocfs2_setattr() could only be the first
> +		 * VFS entry point in the call chain of recursive cluster
> +		 * locking issue.
> +		 *
> +		 * For instance:
> +		 * chmod_common()
> +		 *  notify_change()
> +		 *   ocfs2_setattr()
> +		 *    posix_acl_chmod()
> +		 *     ocfs2_iop_get_acl()
> +		 *
> +		 * But, we're not 100% sure if it's always true, because the
> +		 * ordering of the VFS entry points in the call chain is out
> +		 * of our control. So, we'd better dump the stack here to
> +		 * catch the other cases of recursive locking.
> +		 */
> +		mlog(ML_ERROR, "Another case of recursive locking:\n");
> +		dump_stack();
> +	}
> +	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 +1291,8 @@ 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 +1310,10 @@ 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 +1355,42 @@ int ocfs2_getattr(struct vfsmount *mnt,
>  int ocfs2_permission(struct inode *inode, int mask)
>  {
>  	int ret;
> +	int has_locked;
> +	struct ocfs2_lock_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);
> +	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);
> +	} else {
> +		/* See comments in ocfs2_setattr() for details.
> +		 * The call chain of this case could be:
> +		 * do_sys_open()
> +		 *  may_open()
> +		 *   inode_permission()
> +		 *    ocfs2_permission()
> +		 *     ocfs2_iop_get_acl()
> +		 */
> +		mlog(ML_ERROR, "Another case of recursive locking:\n");
> +		dump_stack();
>  	}
>  
>  	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;
>  }
>