From 69f4cb526bd02ae5af35846f9a710c099eec3347 Mon Sep 17 00:00:00 2001
From: Arne Jansen <sensille@gmx.net>
Date: Fri, 11 Nov 2011 08:17:10 -0500
Subject: [PATCH] Btrfs: handle bio_add_page failure gracefully in scrub

Currently scrub fails with ENOMEM when bio_add_page fails. Unfortunately
dm based targets accept only one page per bio, thus making scrub always
fails. This patch just submits the current bio when an error is encountered
and starts a new one.

Signed-off-by: Arne Jansen <sensille@gmx.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
---
 fs/btrfs/scrub.c | 64 ++++++++++++++++++++++--------------------------
 1 file changed, 29 insertions(+), 35 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index ed11d3866afd..f4190f22edfb 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -944,50 +944,18 @@ static int scrub_checksum_super(struct scrub_bio *sbio, void *buffer)
 static int scrub_submit(struct scrub_dev *sdev)
 {
 	struct scrub_bio *sbio;
-	struct bio *bio;
-	int i;
 
 	if (sdev->curr == -1)
 		return 0;
 
 	sbio = sdev->bios[sdev->curr];
-
-	bio = bio_alloc(GFP_NOFS, sbio->count);
-	if (!bio)
-		goto nomem;
-
-	bio->bi_private = sbio;
-	bio->bi_end_io = scrub_bio_end_io;
-	bio->bi_bdev = sdev->dev->bdev;
-	bio->bi_sector = sbio->physical >> 9;
-
-	for (i = 0; i < sbio->count; ++i) {
-		struct page *page;
-		int ret;
-
-		page = alloc_page(GFP_NOFS);
-		if (!page)
-			goto nomem;
-
-		ret = bio_add_page(bio, page, PAGE_SIZE, 0);
-		if (!ret) {
-			__free_page(page);
-			goto nomem;
-		}
-	}
-
 	sbio->err = 0;
 	sdev->curr = -1;
 	atomic_inc(&sdev->in_flight);
 
-	submit_bio(READ, bio);
+	submit_bio(READ, sbio->bio);
 
 	return 0;
-
-nomem:
-	scrub_free_bio(bio);
-
-	return -ENOMEM;
 }
 
 static int scrub_page(struct scrub_dev *sdev, u64 logical, u64 len,
@@ -995,6 +963,8 @@ static int scrub_page(struct scrub_dev *sdev, u64 logical, u64 len,
 		      u8 *csum, int force)
 {
 	struct scrub_bio *sbio;
+	struct page *page;
+	int ret;
 
 again:
 	/*
@@ -1015,12 +985,22 @@ static int scrub_page(struct scrub_dev *sdev, u64 logical, u64 len,
 	}
 	sbio = sdev->bios[sdev->curr];
 	if (sbio->count == 0) {
+		struct bio *bio;
+
 		sbio->physical = physical;
 		sbio->logical = logical;
+		bio = bio_alloc(GFP_NOFS, SCRUB_PAGES_PER_BIO);
+		if (!bio)
+			return -ENOMEM;
+
+		bio->bi_private = sbio;
+		bio->bi_end_io = scrub_bio_end_io;
+		bio->bi_bdev = sdev->dev->bdev;
+		bio->bi_sector = sbio->physical >> 9;
+		sbio->err = 0;
+		sbio->bio = bio;
 	} else if (sbio->physical + sbio->count * PAGE_SIZE != physical ||
 		   sbio->logical + sbio->count * PAGE_SIZE != logical) {
-		int ret;
-
 		ret = scrub_submit(sdev);
 		if (ret)
 			return ret;
@@ -1030,6 +1010,20 @@ static int scrub_page(struct scrub_dev *sdev, u64 logical, u64 len,
 	sbio->spag[sbio->count].generation = gen;
 	sbio->spag[sbio->count].have_csum = 0;
 	sbio->spag[sbio->count].mirror_num = mirror_num;
+
+	page = alloc_page(GFP_NOFS);
+	if (!page)
+		return -ENOMEM;
+
+	ret = bio_add_page(sbio->bio, page, PAGE_SIZE, 0);
+	if (!ret) {
+		__free_page(page);
+		ret = scrub_submit(sdev);
+		if (ret)
+			return ret;
+		goto again;
+	}
+
 	if (csum) {
 		sbio->spag[sbio->count].have_csum = 1;
 		memcpy(sbio->spag[sbio->count].csum, csum, sdev->csum_size);
-- 
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