NFSv4.2: Rework scratch handling for READ_PLUS (again)

I found that the read code might send multiple requests using the same
nfs_pgio_header, but nfs4_proc_read_setup() is only called once. This is
how we ended up occasionally double-freeing the scratch buffer, but also
means we set a NULL pointer but non-zero length to the xdr scratch
buffer. This results in an oops the first time decoding needs to copy
something to scratch, which frequently happens when decoding READ_PLUS
hole segments.

I fix this by moving scratch handling into the pageio read code. I
provide a function to allocate scratch space for decoding read replies,
and free the scratch buffer when the nfs_pgio_header is freed.

Fixes: fbd2a05f29a9 (NFSv4.2: Rework scratch handling for READ_PLUS)
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

1 files changed, 1 insertions, 12 deletions

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 832fa226b8f2..3c24c3c99e8a 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5438,18 +5438,8 @@ static bool nfs4_read_plus_not_supported(struct rpc_task *task,
 	return false;
 }
 
-static inline void nfs4_read_plus_scratch_free(struct nfs_pgio_header *hdr)
-{
-	if (hdr->res.scratch) {
-		kfree(hdr->res.scratch);
-		hdr->res.scratch = NULL;
-	}
-}
-
 static int nfs4_read_done(struct rpc_task *task, struct nfs_pgio_header *hdr)
 {
-	nfs4_read_plus_scratch_free(hdr);
-
 	if (!nfs4_sequence_done(task, &hdr->res.seq_res))
 		return -EAGAIN;
 	if (nfs4_read_stateid_changed(task, &hdr->args))
@@ -5469,8 +5459,7 @@ static bool nfs42_read_plus_support(struct nfs_pgio_header *hdr,
 	/* Note: We don't use READ_PLUS with pNFS yet */
 	if (nfs_server_capable(hdr->inode, NFS_CAP_READ_PLUS) && !hdr->ds_clp) {
 		msg->rpc_proc = &nfs4_procedures[NFSPROC4_CLNT_READ_PLUS];
-		hdr->res.scratch = kmalloc(32, GFP_KERNEL);
-		return hdr->res.scratch != NULL;
+		return nfs_read_alloc_scratch(hdr, READ_PLUS_SCRATCH_SIZE);
 	}
 	return false;
 }