[SG] Get rid of __sg_mark_end()

sg_mark_end() overwrites the page_link information, but all users want
__sg_mark_end() behaviour where we just set the end bit. That is the most
natural way to use the sg list, since you'll fill it in and then mark the
end point.

So change sg_mark_end() to only set the termination bit. Add a sg_magic
debug check as well, and clear a chain pointer if it is set.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

8 files changed, 21 insertions, 19 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 56f2646612e..54fd3858967 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1369,7 +1369,7 @@ new_segment:
 	} /* segments in rq */
 
 	if (sg)
-		__sg_mark_end(sg);
+		sg_mark_end(sg);
 
 	return nsegs;
 }
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 61fdaf02f25..88de771d356 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -785,7 +785,7 @@ struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
 		 * end-of-list
 		 */
 		if (!left)
-			sg_mark_end(sgl, this);
+			sg_mark_end(&sgl[this - 1]);
 
 		/*
 		 * don't allow subsequent mempool allocs to sleep, it would
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index d5e1876daf3..25973504414 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -188,21 +188,23 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 
 /**
  * sg_mark_end - Mark the end of the scatterlist
- * @sgl:	Scatterlist
- * @nents:	Number of entries in sgl
+ * @sg:		 SG entryScatterlist
  *
  * Description:
- *   Marks the last entry as the termination point for sg_next()
+ *   Marks the passed in sg entry as the termination point for the sg
+ *   table. A call to sg_next() on this entry will return NULL.
  *
  **/
-static inline void sg_mark_end(struct scatterlist *sgl, unsigned int nents)
-{
-	sgl[nents - 1].page_link = 0x02;
-}
-
-static inline void __sg_mark_end(struct scatterlist *sg)
+static inline void sg_mark_end(struct scatterlist *sg)
 {
+#ifdef CONFIG_DEBUG_SG
+	BUG_ON(sg->sg_magic != SG_MAGIC);
+#endif
+	/*
+	 * Set termination bit, clear potential chain bit
+	 */
 	sg->page_link |= 0x02;
+	sg->page_link &= ~0x01;
 }
 
 /**
@@ -218,7 +220,6 @@ static inline void __sg_mark_end(struct scatterlist *sg)
 static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 {
 	memset(sgl, 0, sizeof(*sgl) * nents);
-	sg_mark_end(sgl, nents);
 #ifdef CONFIG_DEBUG_SG
 	{
 		unsigned int i;
@@ -226,6 +227,7 @@ static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 			sgl[i].sg_magic = SG_MAGIC;
 	}
 #endif
+	sg_mark_end(&sgl[nents - 1]);
 }
 
 /**
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 64b50ff7a41..32d5826b717 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2095,7 +2095,7 @@ int skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int le
 {
 	int nsg = __skb_to_sgvec(skb, sg, offset, len);
 
-	__sg_mark_end(&sg[nsg - 1]);
+	sg_mark_end(&sg[nsg - 1]);
 
 	return nsg;
 }
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index eec02b29ffc..d438dfb0c8f 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1083,7 +1083,7 @@ static int tcp_v4_do_calc_md5_hash(char *md5_hash, struct tcp_md5sig_key *key,
 	sg_set_buf(&sg[block++], key->key, key->keylen);
 	nbytes += key->keylen;
 
-	__sg_mark_end(&sg[block - 1]);
+	sg_mark_end(&sg[block - 1]);
 
 	/* Now store the Hash into the packet */
 	err = crypto_hash_init(desc);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 4b903288095..06be2a1f273 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -781,7 +781,7 @@ static int tcp_v6_do_calc_md5_hash(char *md5_hash, struct tcp_md5sig_key *key,
 	sg_set_buf(&sg[block++], key->key, key->keylen);
 	nbytes += key->keylen;
 
-	__sg_mark_end(&sg[block - 1]);
+	sg_mark_end(&sg[block - 1]);
 
 	/* Now store the hash into the packet */
 	err = crypto_hash_init(desc);
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index c387cf68a08..e09a95aa68f 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -702,7 +702,7 @@ static void rxkad_sg_set_buf2(struct scatterlist sg[2],
 		nsg++;
 	}
 
-	__sg_mark_end(&sg[nsg - 1]);
+	sg_mark_end(&sg[nsg - 1]);
 
 	ASSERTCMP(sg[0].length + sg[1].length, ==, buflen);
 }
diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
index ab7cbd6575c..0dd792338fa 100644
--- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
+++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
@@ -211,8 +211,8 @@ encryptor(struct scatterlist *sg, void *data)
 	if (thislen == 0)
 		return 0;
 
-	__sg_mark_end(&desc->infrags[desc->fragno - 1]);
-	__sg_mark_end(&desc->outfrags[desc->fragno - 1]);
+	sg_mark_end(&desc->infrags[desc->fragno - 1]);
+	sg_mark_end(&desc->outfrags[desc->fragno - 1]);
 
 	ret = crypto_blkcipher_encrypt_iv(&desc->desc, desc->outfrags,
 					  desc->infrags, thislen);
@@ -293,7 +293,7 @@ decryptor(struct scatterlist *sg, void *data)
 	if (thislen == 0)
 		return 0;
 
-	__sg_mark_end(&desc->frags[desc->fragno - 1]);
+	sg_mark_end(&desc->frags[desc->fragno - 1]);
 
 	ret = crypto_blkcipher_decrypt_iv(&desc->desc, desc->frags,
 					  desc->frags, thislen);