On Mon, Dec 12, 2022 at 09:31:19AM -0500, Jeff Layton wrote:

On Mon, 2022-12-12 at 14:59 +0100, Greg KH wrote:

quoted

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

quoted

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?

Who the hell sets panic_on_warn (outside of testing environments)?

All cloud providers and anyone else that wants to "kill the system that
had a problem and have it reboot fast" in order to keep things working
overall.

I'm
suggesting a WARN_ON because not finding an entry at this point
represents a bug that we'd want reported.

Your call, but we are generally discouraging adding new WARN_ON() for
anything that userspace could ever trigger.  And if userspace can't
trigger it, then it's a normal type of error that you need to handle
anyway, right?

Anyway, your call, just letting you know.

The caller should hold a reference to the object that holds a vfsmount
reference. It relies on that vfsmount to do a copy. If it's gone at this
point where we're releasing that reference, then we're looking at a
refcounting bug of some sort.

refcounting in the nfsd code, or outside of that?

I would expect anyone who sets panic_on_warn to _desire_ a panic in this
situation. After all, they asked for it. Presumably they want it to do
some coredump analysis or something?

It is debatable whether the stack trace at this point would be helpful
though, so you might consider a pr_warn or something less log-spammy.

If you can recover from it, then yeah, pr_warn() is usually best.

thanks,

greg k-h