[Ocfs2-devel] [PATCH v2] ocfs2: fix deadlock caused by recursive locking in xattr

[Joseph Qi]

Looks good.
Reviewed-by: Joseph Qi <jiangqi903 at gmail.com>

Thanks,
Joseph

On 17/6/22 09:47, Eric Ren wrote:
> Another deadlock path caused by recursive locking is reported.
> This kind of issue was introduced since commit 743b5f1434f5 ("ocfs2:
> take inode lock in ocfs2_iop_set/get_acl()"). Two deadlock paths
> have been fixed by commit b891fa5024a9 ("ocfs2: fix deadlock issue when
> taking inode lock at vfs entry points"). Yes, we intend to fix this
> kind of case in incremental way, because it's hard to find out all
> possible paths at once.
> 
> This one can be reproduced like this. On node1, cp a large file from
> home directory to ocfs2 mountpoint. While on node2, run setfacl/getfacl.
> Both nodes will hang up there. The backtraces:
> 
> On node1:
> [<ffffffffc06a1f67>] __ocfs2_cluster_lock.isra.39+0x357/0x740 [ocfs2]
> [<ffffffffc06a2d3d>] ocfs2_inode_lock_full_nested+0x17d/0x840 [ocfs2]
> [<ffffffffc0692043>] ocfs2_write_begin+0x43/0x1a0 [ocfs2]
> [<ffffffffa21ac719>] generic_perform_write+0xa9/0x180
> [<ffffffffa21aecda>] __generic_file_write_iter+0x1aa/0x1d0
> [<ffffffffc06abc24>] ocfs2_file_write_iter+0x4f4/0xb40 [ocfs2]
> [<ffffffffa223c3b3>] __vfs_write+0xc3/0x130
> [<ffffffffa223cae1>] vfs_write+0xb1/0x1a0
> [<ffffffffa223dfe6>] SyS_write+0x46/0xa0
> 
> On node2:
> [<ffffffffc07b6f67>] __ocfs2_cluster_lock.isra.39+0x357/0x740 [ocfs2]
> [<ffffffffc07b7d3d>] ocfs2_inode_lock_full_nested+0x17d/0x840 [ocfs2]
> [<ffffffffc0815c1e>] ocfs2_xattr_set+0x12e/0xe80 [ocfs2]
> [<ffffffffc081783d>] ocfs2_set_acl+0x22d/0x260 [ocfs2]
> [<ffffffffc08178d5>] ocfs2_iop_set_acl+0x65/0xb0 [ocfs2]
> [<ffffffffa62a43f5>] set_posix_acl+0x75/0xb0
> [<ffffffffa62a4479>] posix_acl_xattr_set+0x49/0xa0
> [<ffffffffa6265c69>] __vfs_setxattr+0x69/0x80
> [<ffffffffa6266832>] __vfs_setxattr_noperm+0x72/0x1a0
> [<ffffffffa6266a07>] vfs_setxattr+0xa7/0xb0
> [<ffffffffa6266b3d>] setxattr+0x12d/0x190
> [<ffffffffa6266c3f>] path_setxattr+0x9f/0xb0
> [<ffffffffa6266d74>] SyS_setxattr+0x14/0x20
> 
> Fixes this one by using ocfs2_inode_{lock|unlock}_tracker, which is
> exported by commit 439a36b8ef38 ("ocfs2/dlmglue: prepare tracking
> logic to avoid recursive cluster lock").
> 
> Changes since v1:
> - Revised git commit description style in commit log.
> 
> Reported-by: Thomas Voegtle <tv at lio96.de>
> Tested-by: Thomas Voegtle <tv at lio96.de>
> Signed-off-by: Eric Ren <zren at suse.com>
> ---
>  fs/ocfs2/dlmglue.c |  4 ++++
>  fs/ocfs2/xattr.c   | 23 +++++++++++++----------
>  2 files changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 3b7c937..4689940 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -2591,6 +2591,10 @@ void ocfs2_inode_unlock_tracker(struct inode *inode,
>  	struct ocfs2_lock_res *lockres;
>  
>  	lockres = &OCFS2_I(inode)->ip_inode_lockres;
> +	/* had_lock means that the currect process already takes the cluster
> +	 * lock previously. If had_lock is 1, we have nothing to do here, and
> +	 * it will get unlocked where we got the lock.
> +	 */
>  	if (!had_lock) {
>  		ocfs2_remove_holder(lockres, oh);
>  		ocfs2_inode_unlock(inode, ex);
> diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
> index 3c5384d..f70c377 100644
> --- a/fs/ocfs2/xattr.c
> +++ b/fs/ocfs2/xattr.c
> @@ -1328,20 +1328,21 @@ static int ocfs2_xattr_get(struct inode *inode,
>  			   void *buffer,
>  			   size_t buffer_size)
>  {
> -	int ret;
> +	int ret, had_lock;
>  	struct buffer_head *di_bh = NULL;
> +	struct ocfs2_lock_holder oh;
>  
> -	ret = ocfs2_inode_lock(inode, &di_bh, 0);
> -	if (ret < 0) {
> -		mlog_errno(ret);
> -		return ret;
> +	had_lock = ocfs2_inode_lock_tracker(inode, &di_bh, 0, &oh);
> +	if (had_lock < 0) {
> +		mlog_errno(had_lock);
> +		return had_lock;
>  	}
>  	down_read(&OCFS2_I(inode)->ip_xattr_sem);
>  	ret = ocfs2_xattr_get_nolock(inode, di_bh, name_index,
>  				     name, buffer, buffer_size);
>  	up_read(&OCFS2_I(inode)->ip_xattr_sem);
>  
> -	ocfs2_inode_unlock(inode, 0);
> +	ocfs2_inode_unlock_tracker(inode, 0, &oh, had_lock);
>  
>  	brelse(di_bh);
>  
> @@ -3537,11 +3538,12 @@ int ocfs2_xattr_set(struct inode *inode,
>  {
>  	struct buffer_head *di_bh = NULL;
>  	struct ocfs2_dinode *di;
> -	int ret, credits, ref_meta = 0, ref_credits = 0;
> +	int ret, credits, had_lock, ref_meta = 0, ref_credits = 0;
>  	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>  	struct inode *tl_inode = osb->osb_tl_inode;
>  	struct ocfs2_xattr_set_ctxt ctxt = { NULL, NULL, NULL, };
>  	struct ocfs2_refcount_tree *ref_tree = NULL;
> +	struct ocfs2_lock_holder oh;
>  
>  	struct ocfs2_xattr_info xi = {
>  		.xi_name_index = name_index,
> @@ -3572,8 +3574,9 @@ int ocfs2_xattr_set(struct inode *inode,
>  		return -ENOMEM;
>  	}
>  
> -	ret = ocfs2_inode_lock(inode, &di_bh, 1);
> -	if (ret < 0) {
> +	had_lock = ocfs2_inode_lock_tracker(inode, &di_bh, 1, &oh);
> +	if (had_lock < 0) {
> +		ret = had_lock;
>  		mlog_errno(ret);
>  		goto cleanup_nolock;
>  	}
> @@ -3670,7 +3673,7 @@ int ocfs2_xattr_set(struct inode *inode,
>  		if (ret)
>  			mlog_errno(ret);
>  	}
> -	ocfs2_inode_unlock(inode, 1);
> +	ocfs2_inode_unlock_tracker(inode, 1, &oh, had_lock);
>  cleanup_nolock:
>  	brelse(di_bh);
>  	brelse(xbs.xattr_bh);
>