Re: [PATCH v3 2/2] ocfs2: fix deadlock issue when taking inode lock at vfs entry points

[Junxiao Bi]

On 01/17/2017 02:30 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:
> - 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>.
> 
> - Change "struct ocfs2_holder" to a more meaningful name "ocfs2_lock_holder",
> suggested by: Junxiao Bi.
> 
> - Add debugging output at ocfs2_setattr() and ocfs2_permission() to
> catch exceptional cases, suggested by: Junxiao Bi.
> 
> Changes since v2:
> - Use new wrappers of tracking logic code, suggested by: Junxiao Bi.
> 
> Signed-off-by: Eric Ren <zren@xxxxxxxx>
Reviewed-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>

> ---
>  fs/ocfs2/acl.c  | 29 +++++++++++++----------------
>  fs/ocfs2/file.c | 58 ++++++++++++++++++++++++++++++++++++++++++++-------------
>  2 files changed, 58 insertions(+), 29 deletions(-)
> 
> diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
> index bed1fcb..dc22ba8 100644
> --- a/fs/ocfs2/acl.c
> +++ b/fs/ocfs2/acl.c
> @@ -283,16 +283,14 @@ int ocfs2_set_acl(handle_t *handle,
>  int ocfs2_iop_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  {
>  	struct buffer_head *bh = NULL;
> -	int status = 0;
> +	int status, had_lock;
> +	struct ocfs2_lock_holder oh;
>  
> -	status = ocfs2_inode_lock(inode, &bh, 1);
> -	if (status < 0) {
> -		if (status != -ENOENT)
> -			mlog_errno(status);
> -		return status;
> -	}
> +	had_lock = ocfs2_inode_lock_tracker(inode, &bh, 1, &oh);
> +	if (had_lock < 0)
> +		return had_lock;
>  	status = ocfs2_set_acl(NULL, inode, bh, type, acl, NULL, NULL);
> -	ocfs2_inode_unlock(inode, 1);
> +	ocfs2_inode_unlock_tracker(inode, 1, &oh, had_lock);
>  	brelse(bh);
>  	return status;
>  }
> @@ -302,21 +300,20 @@ struct posix_acl *ocfs2_iop_get_acl(struct inode *inode, int type)
>  	struct ocfs2_super *osb;
>  	struct buffer_head *di_bh = NULL;
>  	struct posix_acl *acl;
> -	int ret;
> +	int had_lock;
> +	struct ocfs2_lock_holder oh;
>  
>  	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);
> -	if (ret < 0) {
> -		if (ret != -ENOENT)
> -			mlog_errno(ret);
> -		return ERR_PTR(ret);
> -	}
> +
> +	had_lock = ocfs2_inode_lock_tracker(inode, &di_bh, 0, &oh);
> +	if (had_lock < 0)
> +		return ERR_PTR(had_lock);
>  
>  	acl = ocfs2_get_acl_nolock(inode, type, di_bh);
>  
> -	ocfs2_inode_unlock(inode, 0);
> +	ocfs2_inode_unlock_tracker(inode, 0, &oh, had_lock);
>  	brelse(di_bh);
>  	return acl;
>  }
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index c488965..7b6a146 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -1138,6 +1138,8 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>  	handle_t *handle = NULL;
>  	struct dquot *transfer_to[MAXQUOTAS] = { };
>  	int qtype;
> +	int had_lock;
> +	struct ocfs2_lock_holder oh;
>  
>  	trace_ocfs2_setattr(inode, dentry,
>  			    (unsigned long long)OCFS2_I(inode)->ip_blkno,
> @@ -1173,11 +1175,30 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>  		}
>  	}
>  
> -	status = ocfs2_inode_lock(inode, &bh, 1);
> -	if (status < 0) {
> -		if (status != -ENOENT)
> -			mlog_errno(status);
> +	had_lock = ocfs2_inode_lock_tracker(inode, &bh, 1, &oh);
> +	if (had_lock < 0) {
> +		status = had_lock;
>  		goto bail_unlock_rw;
> +	} else if (had_lock) {
> +		/*
> +		 * 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();
>  	}
>  	inode_locked = 1;
>  
> @@ -1260,8 +1281,8 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>  bail_commit:
>  	ocfs2_commit_trans(osb, handle);
>  bail_unlock:
> -	if (status) {
> -		ocfs2_inode_unlock(inode, 1);
> +	if (status && inode_locked) {
> +		ocfs2_inode_unlock_tracker(inode, 1, &oh, had_lock);
>  		inode_locked = 0;
>  	}
>  bail_unlock_rw:
> @@ -1279,7 +1300,7 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>  			mlog_errno(status);
>  	}
>  	if (inode_locked)
> -		ocfs2_inode_unlock(inode, 1);
> +		ocfs2_inode_unlock_tracker(inode, 1, &oh, had_lock);
>  
>  	brelse(bh);
>  	return status;
> @@ -1320,21 +1341,32 @@ int ocfs2_getattr(struct vfsmount *mnt,
>  
>  int ocfs2_permission(struct inode *inode, int mask)
>  {
> -	int ret;
> +	int ret, had_lock;
> +	struct ocfs2_lock_holder oh;
>  
>  	if (mask & MAY_NOT_BLOCK)
>  		return -ECHILD;
>  
> -	ret = ocfs2_inode_lock(inode, NULL, 0);
> -	if (ret) {
> -		if (ret != -ENOENT)
> -			mlog_errno(ret);
> +	had_lock = ocfs2_inode_lock_tracker(inode, NULL, 0, &oh);
> +	if (had_lock < 0) {
> +		ret = had_lock;
>  		goto out;
> +	} else if (had_lock) {
> +		/* 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);
> +	ocfs2_inode_unlock_tracker(inode, 0, &oh, had_lock);
>  out:
>  	return ret;
>  }
>