[PATCH v2 1/2] NFS: Fix O_DIRECT accounting of number of bytes read/written

[Trond Myklebust <trondmy@gmail.com>]

When a series of O_DIRECT reads or writes are truncated, either due to
eof or due to an error, then we should return the number of contiguous
bytes that were received/sent starting at the offset specified by the
application.

Currently, we are failing to correctly check contiguity, and so we're
failing the generic/465 in xfstests when the race between the read
and write RPCs causes the file to get extended while the 2 reads are
outstanding. If the first read RPC call wins the race and returns with
eof set, we should treat the second read RPC as being truncated.

Reported-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
Fixes: 1ccbad9f9f9bd ("nfs: fix DIO good bytes calculation")
Cc: stable@vger.kernel.org # 4.1+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/direct.c | 82 ++++++++++++++++++++++++++++---------------------
 1 file changed, 47 insertions(+), 35 deletions(-)

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 222d7115db71..62cb4a1a87f0 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -123,32 +123,53 @@ static inline int put_dreq(struct nfs_direct_req *dreq)
 }
 
 static void
-nfs_direct_good_bytes(struct nfs_direct_req *dreq, struct nfs_pgio_header *hdr)
+nfs_direct_handle_truncated(struct nfs_direct_req *dreq,
+			    const struct nfs_pgio_header *hdr,
+			    ssize_t dreq_len)
 {
-	int i;
-	ssize_t count;
+	struct nfs_direct_mirror *mirror = &dreq->mirrors[hdr->pgio_mirror_idx];
+	loff_t hdr_arg = hdr->io_start + hdr->args.count;
+	ssize_t expected = 0;
+
+	if (hdr_arg > dreq->io_start)
+		expected = hdr_arg - dreq->io_start;
+
+	if (dreq_len == expected)
+		return;
+	if (dreq->max_count > dreq_len) {
+		dreq->max_count = dreq_len;
+		if (dreq->count > dreq_len)
+			dreq->count = dreq_len;
+
+		if (test_bit(NFS_IOHDR_ERROR, &hdr->flags))
+			dreq->error = hdr->error;
+		else if (hdr->good_bytes > 0)
+			dreq->error = 0;
+	}
+	if (mirror->count > dreq_len)
+		mirror->count = dreq_len;
+}
 
-	WARN_ON_ONCE(dreq->count >= dreq->max_count);
+static void
+nfs_direct_count_bytes(struct nfs_direct_req *dreq,
+		       const struct nfs_pgio_header *hdr)
+{
+	struct nfs_direct_mirror *mirror = &dreq->mirrors[hdr->pgio_mirror_idx];
+	loff_t hdr_end = hdr->io_start + hdr->good_bytes;
+	ssize_t dreq_len = 0;
 
-	if (dreq->mirror_count == 1) {
-		dreq->mirrors[hdr->pgio_mirror_idx].count += hdr->good_bytes;
-		dreq->count += hdr->good_bytes;
-	} else {
-		/* mirrored writes */
-		count = dreq->mirrors[hdr->pgio_mirror_idx].count;
-		if (count + dreq->io_start < hdr->io_start + hdr->good_bytes) {
-			count = hdr->io_start + hdr->good_bytes - dreq->io_start;
-			dreq->mirrors[hdr->pgio_mirror_idx].count = count;
-		}
-		/* update the dreq->count by finding the minimum agreed count from all
-		 * mirrors */
-		count = dreq->mirrors[0].count;
+	if (hdr_end > dreq->io_start)
+		dreq_len = hdr_end - dreq->io_start;
 
-		for (i = 1; i < dreq->mirror_count; i++)
-			count = min(count, dreq->mirrors[i].count);
+	nfs_direct_handle_truncated(dreq, hdr, dreq_len);
 
-		dreq->count = count;
-	}
+	if (dreq_len > dreq->max_count)
+		dreq_len = dreq->max_count;
+
+	if (mirror->count < dreq_len)
+		mirror->count = dreq_len;
+	if (dreq->count < dreq_len)
+		dreq->count = dreq_len;
 }
 
 /*
@@ -402,20 +423,12 @@ static void nfs_direct_read_completion(struct nfs_pgio_header *hdr)
 	struct nfs_direct_req *dreq = hdr->dreq;
 
 	spin_lock(&dreq->lock);
-	if (test_bit(NFS_IOHDR_ERROR, &hdr->flags))
-		dreq->error = hdr->error;
-
 	if (test_bit(NFS_IOHDR_REDO, &hdr->flags)) {
 		spin_unlock(&dreq->lock);
 		goto out_put;
 	}
 
-	if (hdr->good_bytes != 0)
-		nfs_direct_good_bytes(dreq, hdr);
-
-	if (test_bit(NFS_IOHDR_EOF, &hdr->flags))
-		dreq->error = 0;
-
+	nfs_direct_count_bytes(dreq, hdr);
 	spin_unlock(&dreq->lock);
 
 	while (!list_empty(&hdr->pages)) {
@@ -652,6 +665,9 @@ static void nfs_direct_write_reschedule(struct nfs_direct_req *dreq)
 	nfs_direct_write_scan_commit_list(dreq->inode, &reqs, &cinfo);
 
 	dreq->count = 0;
+	dreq->max_count = 0;
+	list_for_each_entry(req, &reqs, wb_list)
+		dreq->max_count += req->wb_bytes;
 	dreq->verf.committed = NFS_INVALID_STABLE_HOW;
 	nfs_clear_pnfs_ds_commit_verifiers(&dreq->ds_cinfo);
 	for (i = 0; i < dreq->mirror_count; i++)
@@ -791,17 +807,13 @@ static void nfs_direct_write_completion(struct nfs_pgio_header *hdr)
 	nfs_init_cinfo_from_dreq(&cinfo, dreq);
 
 	spin_lock(&dreq->lock);
-
-	if (test_bit(NFS_IOHDR_ERROR, &hdr->flags))
-		dreq->error = hdr->error;
-
 	if (test_bit(NFS_IOHDR_REDO, &hdr->flags)) {
 		spin_unlock(&dreq->lock);
 		goto out_put;
 	}
 
+	nfs_direct_count_bytes(dreq, hdr);
 	if (hdr->good_bytes != 0) {
-		nfs_direct_good_bytes(dreq, hdr);
 		if (nfs_write_need_commit(hdr)) {
 			if (dreq->flags == NFS_ODIRECT_RESCHED_WRITES)
 				request_commit = true;
-- 
2.21.0