On Mon, Dec 12, 2022 at 08:40:31AM -0500, Jeff Layton wrote:

On Mon, 2022-12-12 at 05:34 -0800, dai.ngo@oracle.com wrote:

quoted

On 12/12/22 4:22 AM, Jeff Layton wrote:

quoted

On Sun, 2022-12-11 at 11:22 -0800, Dai Ngo wrote:

quoted

Problem caused by source's vfsmount being unmounted but remains
on the delayed unmount list. This happens when nfs42_ssc_open()
return errors.
Fixed by removing nfsd4_interssc_connect(), leave the vfsmount
for the laundromat to unmount when idle time expires.

Reported-by: Xingyuan Mo <redacted>
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
  fs/nfsd/nfs4proc.c | 23 +++++++----------------
  1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 8beb2bc4c328..756e42cf0d01 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c

@@ -1463,13 +1463,6 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
  	return status;
  }
  
-static void
-nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
-{
-	nfs_do_sb_deactive(ss_mnt->mnt_sb);
-	mntput(ss_mnt);
-}
-
  /*
   * Verify COPY destination stateid.
   *

@@ -1572,11 +1565,6 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct file *filp,
  {
  }
  
-static void
-nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
-{
-}
-
  static struct file *nfs42_ssc_open(struct vfsmount *ss_mnt,
  				   struct nfs_fh *src_fh,
  				   nfs4_stateid *stateid)

@@ -1762,7 +1750,8 @@ static int nfsd4_do_async_copy(void *data)
  		struct file *filp;
  
  		filp = nfs42_ssc_open(copy->ss_mnt, &copy->c_fh,
-				      &copy->stateid);
+					&copy->stateid);
+
  		if (IS_ERR(filp)) {
  			switch (PTR_ERR(filp)) {
  			case -EBADF:

@@ -1771,7 +1760,7 @@ static int nfsd4_do_async_copy(void *data)
  			default:
  				nfserr = nfserr_offload_denied;
  			}
-			nfsd4_interssc_disconnect(copy->ss_mnt);
+			/* ss_mnt will be unmounted by the laundromat */
  			goto do_callback;
  		}
  		nfserr = nfsd4_do_copy(copy, filp, copy->nf_dst->nf_file,

@@ -1852,8 +1841,10 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
  	if (async_copy)
  		cleanup_async_copy(async_copy);
  	status = nfserrno(-ENOMEM);
-	if (nfsd4_ssc_is_inter(copy))
-		nfsd4_interssc_disconnect(copy->ss_mnt);
+	/*
+	 * source's vfsmount of inter-copy will be unmounted
+	 * by the laundromat
+	 */
  	goto out;
  }
  

This looks reasonable at first glance, but I have some concerns with the
refcounting around ss_mnt elsewhere in this code. nfsd4_ssc_setup_dul
looks for an existing connection and bumps the ni->nsui_refcnt if it
finds one.

But then later, nfsd4_cleanup_inter_ssc has a couple of cases where it
just does a bare mntput:

         if (!nn) {
                 mntput(ss_mnt);
                 return;
         }
...
         if (!found) {
                 mntput(ss_mnt);
                 return;
         }

The first one looks bogus. Can net_generic return NULL? If so how, and
why is it not a problem elsewhere in the kernel?

it looks like net_generic can not fail, no where else check for NULL
so I will remove this check.

quoted

For the second case, if the ni is no longer on the list, where did the
extra ss_mnt reference come from? Maybe that should be a WARN_ON or
BUG_ON?

if ni is not found on the list then it's a bug somewhere so I will add
a BUG_ON on this.

Probably better to just WARN_ON and let any references leak in that
case. A BUG_ON implies a panic in some environments, and it's best to
avoid that unless there really is no choice.

WARN_ON also causes machines to boot that have panic_on_warn enabled.
Why not just handle the error and keep going?  Why panic at all?

thanks,

greg k-h