[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>

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;
 }

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

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]);
 }
 
 /**

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;
 }

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);

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);

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);
 }

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);