[PATCH] NFS: Fixes for nfs4_proc_mkdir() error handling

[Anna Schumaker <anna@kernel.org>]

From: Anna Schumaker <anna.schumaker@oracle.com>

The PTR_ERR_OR_ZERO() macro uses IS_ERR(), which checks if an error
value is a valid Linux error code. It does not take into account NFS
error codes, which are well out of the range of MAX_ERRNO. So if
_nfs4_proc_mkdir() returns -NFS4ERR_DELAY (which xfstests generic/477 was
able to consistently hit while running against a Hammerspace server),
PTR_ERR_OR_ZERO() will happily say "no, that's not an error", so we
propagate it up to the VFS who then tries to dput() it.

Naturally, the kernel doesn't like this:

[  247.669307] BUG: unable to handle page fault for address: ffffffffffffd968
[  247.690824] RIP: 0010:lockref_put_return+0x67/0x130
[  247.719037] Call Trace:
[  247.719446]  <TASK>
[  247.719806]  ? __pfx_lockref_put_return+0x10/0x10
[  247.720538]  ? _raw_spin_unlock+0x15/0x30
[  247.721173]  ? dput+0x179/0x490
[  247.721682]  ? vfs_mkdir+0x475/0x780
[  247.722259]  dput+0x30/0x490
[  247.722730]  do_mkdirat+0x158/0x310
[  247.723292]  ? __pfx_do_mkdirat+0x10/0x10
[  247.723928]  __x64_sys_mkdir+0xd3/0x160
[  247.724531]  do_syscall_64+0x4b/0x120
[  247.725131]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  247.725914] RIP: 0033:0x7fe0e22f3ddb

While I was in the area, I noticed that we're discarding any errors left
unhandled by nfs4_handle_exception(). This patch fixes both of these
issues.

Fixes: 8376583b84a1 ("nfs: change mkdir inode_operation to return alternate dentry if needed.")
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
---
 fs/nfs/nfs4proc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index c7e068b563ff..306dade146e6 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5274,13 +5274,17 @@ static struct dentry *nfs4_proc_mkdir(struct inode *dir, struct dentry *dentry,
 		sattr->ia_mode &= ~current_umask();
 	do {
 		alias = _nfs4_proc_mkdir(dir, dentry, sattr, label);
-		err = PTR_ERR_OR_ZERO(alias);
+		err = PTR_ERR(alias);
+		if (err > 0)
+			err = 0;
 		trace_nfs4_mkdir(dir, &dentry->d_name, err);
 		err = nfs4_handle_exception(NFS_SERVER(dir), err,
 				&exception);
 	} while (exception.retry);
 	nfs4_label_release_security(label);
 
+	if (err != 0)
+		return ERR_PTR(err);
 	return alias;
 }
 
-- 
2.49.0