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Sender: Chuck Lever <chucklever@gmail.com>
Subject: [PATCH v1] NFS: Fix rpcrdma_inline_fixup() crash with new LISTXATTRS
 operation
From:   Chuck Lever <chuck.lever@oracle.com>
To:     kolga@netapp.com, fllinden@amazon.com
Cc:     linux-nfs@vger.kernel.org
Date:   Tue, 24 Nov 2020 12:26:32 -0500
Message-ID: <160623862874.1534.4471924380357882531.stgit@manet.1015granger.net>
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By switching to an XFS-backed export, I am able to reproduce the
ibcomp worker crash on my client with xfstests generic/013.

For the failing LISTXATTRS operation, xdr_inline_pages() is called
with page_len=12 and buflen=128. Then:

- Because buflen is small, rpcrdma_marshal_req will not set up a
  Reply chunk and the rpcrdma's XDRBUF_SPARSE_PAGES logic does not
  get invoked at all.

- Because page_len is non-zero, rpcrdma_inline_fixup() tries to
  copy received data into rq_rcv_buf->pages, but they're missing.

The result is that the ibcomp worker faults and dies. Sometimes that
causes a visible crash, and sometimes it results in a transport
hang without other symptoms.

RPC/RDMA's XDRBUF_SPARSE_PAGES support is not entirely correct, and
should eventually be fixed or replaced. However, my preference is
that upper-layer operations should explicitly allocate their receive
buffers (using GFP_KERNEL) when possible, rather than relying on
XDRBUF_SPARSE_PAGES.

Reported-by: Olga kornievskaia <kolga@netapp.com>
Suggested-by: Olga kornievskaia <kolga@netapp.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfs/nfs42proc.c |   17 ++++++++++-------
 fs/nfs/nfs42xdr.c  |    1 -
 2 files changed, 10 insertions(+), 8 deletions(-)

Hi-

I like Olga's proposed approach. What do you think of this patch?


diff --git a/fs/nfs/nfs42proc.c b/fs/nfs/nfs42proc.c
index 2b2211d1234e..24810305ec1c 100644
--- a/fs/nfs/nfs42proc.c
+++ b/fs/nfs/nfs42proc.c
@@ -1241,7 +1241,7 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
 		.rpc_resp	= &res,
 	};
 	u32 xdrlen;
-	int ret, np;
+	int ret, np, i;
 
 
 	res.scratch = alloc_page(GFP_KERNEL);
@@ -1253,10 +1253,14 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
 		xdrlen = server->lxasize;
 	np = xdrlen / PAGE_SIZE + 1;
 
+	ret = -ENOMEM;
 	pages = kcalloc(np, sizeof(struct page *), GFP_KERNEL);
-	if (pages == NULL) {
-		__free_page(res.scratch);
-		return -ENOMEM;
+	if (pages == NULL)
+		goto out_free;
+	for (i = 0; i < np; i++) {
+		pages[i] = alloc_page(GFP_KERNEL);
+		if (!pages[i])
+			goto out_free;
 	}
 
 	arg.xattr_pages = pages;
@@ -1271,14 +1275,13 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
 		*eofp = res.eof;
 	}
 
+out_free:
 	while (--np >= 0) {
 		if (pages[np])
 			__free_page(pages[np]);
 	}
-
-	__free_page(res.scratch);
 	kfree(pages);
-
+	__free_page(res.scratch);
 	return ret;
 
 }
diff --git a/fs/nfs/nfs42xdr.c b/fs/nfs/nfs42xdr.c
index 6e060a88f98c..8432bd6b95f0 100644
--- a/fs/nfs/nfs42xdr.c
+++ b/fs/nfs/nfs42xdr.c
@@ -1528,7 +1528,6 @@ static void nfs4_xdr_enc_listxattrs(struct rpc_rqst *req,
 
 	rpc_prepare_reply_pages(req, args->xattr_pages, 0, args->count,
 	    hdr.replen);
-	req->rq_rcv_buf.flags |= XDRBUF_SPARSE_PAGES;
 
 	encode_nops(&hdr);
 }