btrfs scrub: make fixups sync

btrfs scrub - make fixups sync, don't reuse fixup bios

Fixups are already sync for csum failures, this patch makes them sync
for EIO case as well.

Fixups are now sharing pages with the parent sbio - instead of
allocating a separate page to do a fixup we grab the page from the sbio
buffer.

Fixup bios are no longer reused.

struct fixup is no longer needed, instead pass [sbio pointer, index].

Originally this was added to look at the possibility of sharing the code
between drive swap and scrub, but it actually fixes a serious bug in
scrub code where errors that could be corrected were ignored and
reported as uncorrectable.

btrfs scrub - restore bios properly after media errors

The current code reallocates a bio after a media error.  This is a
temporary measure introduced in v3 after a serious problem related to
bio reuse was found in v2 of scrub patchset.

Basically we did not reset bv_offset and bv_len fields of the bio_vec
structure.  They are changed in case I/O error happens, for example, at
offset 512 or 1024 into the page.  Also bi_flags field wasn't properly
setup before reusing the bio.
Signed-off-by: Arne Jansen <sensille@gmx.net>

fs/btrfs/scrub.c

@@ -50,7 +50,6 @@
 struct scrub_bio;
 struct scrub_page;
 struct scrub_dev;
-struct scrub_fixup;
 static void scrub_bio_end_io(struct bio *bio, int err);
 static void scrub_checksum(struct btrfs_work *work);
 static int scrub_checksum_data(struct scrub_dev *sdev,
@@ -59,9 +58,11 @@ static int scrub_checksum_tree_block(struct scrub_dev *sdev,
 				     struct scrub_page *spag, u64 logical,
 				     void *buffer);
 static int scrub_checksum_super(struct scrub_bio *sbio, void *buffer);
-static void scrub_recheck_end_io(struct bio *bio, int err);
-static void scrub_fixup_worker(struct btrfs_work *work);
-static void scrub_fixup(struct scrub_fixup *fixup);
+static int scrub_fixup_check(struct scrub_bio *sbio, int ix);
+static void scrub_fixup_end_io(struct bio *bio, int err);
+static int scrub_fixup_io(int rw, struct block_device *bdev, sector_t sector,
+			  struct page *page);
+static void scrub_fixup(struct scrub_bio *sbio, int ix);
 
 #define SCRUB_PAGES_PER_BIO	16	/* 64k per bio */
 #define SCRUB_BIOS_PER_DEV	16	/* 1 MB per device in flight */
@@ -105,17 +106,6 @@ struct scrub_dev {
 	spinlock_t		stat_lock;
 };
 
-struct scrub_fixup {
-	struct scrub_dev	*sdev;
-	struct bio		*bio;
-	u64			logical;
-	u64			physical;
-	struct scrub_page	spag;
-	struct btrfs_work	work;
-	int			err;
-	int			recheck;
-};
-
 static void scrub_free_csums(struct scrub_dev *sdev)
 {
 	while (!list_empty(&sdev->csum_list)) {
@@ -240,107 +230,34 @@ struct scrub_dev *scrub_setup_dev(struct btrfs_device *dev)
  */
 static void scrub_recheck_error(struct scrub_bio *sbio, int ix)
 {
-	struct scrub_dev *sdev = sbio->sdev;
-	struct btrfs_fs_info *fs_info = sdev->dev->dev_root->fs_info;
-	struct bio *bio = NULL;
-	struct page *page = NULL;
-	struct scrub_fixup *fixup = NULL;
-	int ret;
-
-	/*
-	 * while we're in here we do not want the transaction to commit.
-	 * To prevent it, we increment scrubs_running. scrub_pause will
-	 * have to wait until we're finished
-	 * we can safely increment scrubs_running here, because we're
-	 * in the context of the original bio which is still marked in_flight
-	 */
-	atomic_inc(&fs_info->scrubs_running);
-
-	fixup = kzalloc(sizeof(*fixup), GFP_NOFS);
-	if (!fixup)
-		goto malloc_error;
-
-	fixup->logical = sbio->logical + ix * PAGE_SIZE;
-	fixup->physical = sbio->physical + ix * PAGE_SIZE;
-	fixup->spag = sbio->spag[ix];
-	fixup->sdev = sdev;
-
-	bio = bio_alloc(GFP_NOFS, 1);
-	if (!bio)
-		goto malloc_error;
-	bio->bi_private = fixup;
-	bio->bi_size = 0;
-	bio->bi_bdev = sdev->dev->bdev;
-	fixup->bio = bio;
-	fixup->recheck = 0;
-
-	page = alloc_page(GFP_NOFS);
-	if (!page)
-		goto malloc_error;
-
-	ret = bio_add_page(bio, page, PAGE_SIZE, 0);
-	if (!ret)
-		goto malloc_error;
-
-	if (!sbio->err) {
-		/*
-		 * shorter path: just a checksum error, go ahead and correct it
-		 */
-		scrub_fixup_worker(&fixup->work);
-		return;
+	if (sbio->err) {
+		if (scrub_fixup_io(READ, sbio->sdev->dev->bdev,
+				   (sbio->physical + ix * PAGE_SIZE) >> 9,
+				   sbio->bio->bi_io_vec[ix].bv_page) == 0) {
+			if (scrub_fixup_check(sbio, ix) == 0)
+				return;
+		}
 	}
 
-	/*
-	 * an I/O-error occured for one of the blocks in the bio, not
-	 * necessarily for this one, so first try to read it separately
-	 */
-	fixup->work.func = scrub_fixup_worker;
-	fixup->recheck = 1;
-	bio->bi_end_io = scrub_recheck_end_io;
-	bio->bi_sector = fixup->physical >> 9;
-	bio->bi_bdev = sdev->dev->bdev;
-	submit_bio(0, bio);
-
-	return;
-
-malloc_error:
-	if (bio)
-		bio_put(bio);
-	if (page)
-		__free_page(page);
-	kfree(fixup);
-	spin_lock(&sdev->stat_lock);
-	++sdev->stat.malloc_errors;
-	spin_unlock(&sdev->stat_lock);
-	atomic_dec(&fs_info->scrubs_running);
-	wake_up(&fs_info->scrub_pause_wait);
+	scrub_fixup(sbio, ix);
 }
 
-static void scrub_recheck_end_io(struct bio *bio, int err)
-{
-	struct scrub_fixup *fixup = bio->bi_private;
-	struct btrfs_fs_info *fs_info = fixup->sdev->dev->dev_root->fs_info;
-
-	fixup->err = err;
-	btrfs_queue_worker(&fs_info->scrub_workers, &fixup->work);
-}
-
-static int scrub_fixup_check(struct scrub_fixup *fixup)
+static int scrub_fixup_check(struct scrub_bio *sbio, int ix)
 {
 	int ret = 1;
 	struct page *page;
 	void *buffer;
-	u64 flags = fixup->spag.flags;
+	u64 flags = sbio->spag[ix].flags;
 
-	page = fixup->bio->bi_io_vec[0].bv_page;
+	page = sbio->bio->bi_io_vec[ix].bv_page;
 	buffer = kmap_atomic(page, KM_USER0);
 	if (flags & BTRFS_EXTENT_FLAG_DATA) {
-		ret = scrub_checksum_data(fixup->sdev,
-					  &fixup->spag, buffer);
+		ret = scrub_checksum_data(sbio->sdev,
+					  sbio->spag + ix, buffer);
 	} else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
-		ret = scrub_checksum_tree_block(fixup->sdev,
-						&fixup->spag,
-						fixup->logical,
+		ret = scrub_checksum_tree_block(sbio->sdev,
+						sbio->spag + ix,
+						sbio->logical + ix * PAGE_SIZE,
 						buffer);
 	} else {
 		WARN_ON(1);
@@ -350,51 +267,25 @@ static int scrub_fixup_check(struct scrub_fixup *fixup)
 	return ret;
 }
 
-static void scrub_fixup_worker(struct btrfs_work *work)
-{
-	struct scrub_fixup *fixup;
-	struct btrfs_fs_info *fs_info;
-	u64 flags;
-	int ret = 1;
-
-	fixup = container_of(work, struct scrub_fixup, work);
-	fs_info = fixup->sdev->dev->dev_root->fs_info;
-	flags = fixup->spag.flags;
-
-	if (fixup->recheck && fixup->err == 0)
-		ret = scrub_fixup_check(fixup);
-
-	if (ret || fixup->err)
-		scrub_fixup(fixup);
-
-	__free_page(fixup->bio->bi_io_vec[0].bv_page);
-	bio_put(fixup->bio);
-
-	atomic_dec(&fs_info->scrubs_running);
-	wake_up(&fs_info->scrub_pause_wait);
-
-	kfree(fixup);
-}
-
 static void scrub_fixup_end_io(struct bio *bio, int err)
 {
 	complete((struct completion *)bio->bi_private);
 }
 
-static void scrub_fixup(struct scrub_fixup *fixup)
+static void scrub_fixup(struct scrub_bio *sbio, int ix)
 {
-	struct scrub_dev *sdev = fixup->sdev;
+	struct scrub_dev *sdev = sbio->sdev;
 	struct btrfs_fs_info *fs_info = sdev->dev->dev_root->fs_info;
 	struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
 	struct btrfs_multi_bio *multi = NULL;
-	struct bio *bio = fixup->bio;
+	u64 logical = sbio->logical + ix * PAGE_SIZE;
 	u64 length;
 	int i;
 	int ret;
 	DECLARE_COMPLETION_ONSTACK(complete);
 
-	if ((fixup->spag.flags & BTRFS_EXTENT_FLAG_DATA) &&
-	    (fixup->spag.have_csum == 0)) {
+	if ((sbio->spag[ix].flags & BTRFS_EXTENT_FLAG_DATA) &&
+	    (sbio->spag[ix].have_csum == 0)) {
 		/*
 		 * nodatasum, don't try to fix anything
 		 * FIXME: we can do better, open the inode and trigger a
@@ -404,71 +295,49 @@ static void scrub_fixup(struct scrub_fixup *fixup)
 	}
 
 	length = PAGE_SIZE;
-	ret = btrfs_map_block(map_tree, REQ_WRITE, fixup->logical, &length,
+	ret = btrfs_map_block(map_tree, REQ_WRITE, logical, &length,
 			      &multi, 0);
 	if (ret || !multi || length < PAGE_SIZE) {
 		printk(KERN_ERR
 		       "scrub_fixup: btrfs_map_block failed us for %llu\n",
-		       (unsigned long long)fixup->logical);
+		       (unsigned long long)logical);
 		WARN_ON(1);
 		return;
 	}
 
-	if (multi->num_stripes == 1) {
+	if (multi->num_stripes == 1)
 		/* there aren't any replicas */
 		goto uncorrectable;
-	}
 
 	/*
 	 * first find a good copy
 	 */
 	for (i = 0; i < multi->num_stripes; ++i) {
-		if (i == fixup->spag.mirror_num)
+		if (i == sbio->spag[ix].mirror_num)
 			continue;
 
-		bio->bi_sector = multi->stripes[i].physical >> 9;
-		bio->bi_bdev = multi->stripes[i].dev->bdev;
-		bio->bi_size = PAGE_SIZE;
-		bio->bi_next = NULL;
-		bio->bi_flags |= 1 << BIO_UPTODATE;
-		bio->bi_comp_cpu = -1;
-		bio->bi_end_io = scrub_fixup_end_io;
-		bio->bi_private = &complete;
-
-		submit_bio(0, bio);
-
-		wait_for_completion(&complete);
-
-		if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
+		if (scrub_fixup_io(READ, multi->stripes[i].dev->bdev,
+				   multi->stripes[i].physical >> 9,
+				   sbio->bio->bi_io_vec[ix].bv_page)) {
 			/* I/O-error, this is not a good copy */
 			continue;
+		}
 
-		ret = scrub_fixup_check(fixup);
-		if (ret == 0)
+		if (scrub_fixup_check(sbio, ix) == 0)
 			break;
 	}
 	if (i == multi->num_stripes)
 		goto uncorrectable;
 
 	/*
-	 * the bio now contains good data, write it back
+	 * bi_io_vec[ix].bv_page now contains good data, write it back
 	 */
-	bio->bi_sector = fixup->physical >> 9;
-	bio->bi_bdev = sdev->dev->bdev;
-	bio->bi_size = PAGE_SIZE;
-	bio->bi_next = NULL;
-	bio->bi_flags |= 1 << BIO_UPTODATE;
-	bio->bi_comp_cpu = -1;
-	bio->bi_end_io = scrub_fixup_end_io;
-	bio->bi_private = &complete;
-
-	submit_bio(REQ_WRITE, bio);
-
-	wait_for_completion(&complete);
-
-	if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
+	if (scrub_fixup_io(WRITE, sdev->dev->bdev,
+			   (sbio->physical + ix * PAGE_SIZE) >> 9,
+			   sbio->bio->bi_io_vec[ix].bv_page)) {
 		/* I/O-error, writeback failed, give up */
 		goto uncorrectable;
+	}
 
 	kfree(multi);
 	spin_lock(&sdev->stat_lock);
@@ -477,7 +346,7 @@ static void scrub_fixup(struct scrub_fixup *fixup)
 
 	if (printk_ratelimit())
 		printk(KERN_ERR "btrfs: fixed up at %llu\n",
-		       (unsigned long long)fixup->logical);
+		       (unsigned long long)logical);
 	return;
 
 uncorrectable:
@@ -488,7 +357,32 @@ static void scrub_fixup(struct scrub_fixup *fixup)
 
 	if (printk_ratelimit())
 		printk(KERN_ERR "btrfs: unable to fixup at %llu\n",
-			 (unsigned long long)fixup->logical);
+			 (unsigned long long)logical);
+}
+
+static int scrub_fixup_io(int rw, struct block_device *bdev, sector_t sector,
+			 struct page *page)
+{
+	struct bio *bio = NULL;
+	int ret;
+	DECLARE_COMPLETION_ONSTACK(complete);
+
+	/* we are going to wait on this IO */
+	rw |= REQ_SYNC | REQ_UNPLUG;
+
+	bio = bio_alloc(GFP_NOFS, 1);
+	bio->bi_bdev = bdev;
+	bio->bi_sector = sector;
+	bio_add_page(bio, page, PAGE_SIZE, 0);
+	bio->bi_end_io = scrub_fixup_end_io;
+	bio->bi_private = &complete;
+	submit_bio(rw, bio);
+
+	wait_for_completion(&complete);
+
+	ret = !test_bit(BIO_UPTODATE, &bio->bi_flags);
+	bio_put(bio);
+	return ret;
 }
 
 static void scrub_bio_end_io(struct bio *bio, int err)
@@ -514,44 +408,24 @@ static void scrub_checksum(struct btrfs_work *work)
 	int ret;
 
 	if (sbio->err) {
-		struct bio *bio;
-		struct bio *old_bio;
-
 		for (i = 0; i < sbio->count; ++i)
 			scrub_recheck_error(sbio, i);
+
+		sbio->bio->bi_flags &= ~(BIO_POOL_MASK - 1);
+		sbio->bio->bi_flags |= 1 << BIO_UPTODATE;
+		sbio->bio->bi_phys_segments = 0;
+		sbio->bio->bi_idx = 0;
+
+		for (i = 0; i < sbio->count; i++) {
+			struct bio_vec *bi;
+			bi = &sbio->bio->bi_io_vec[i];
+			bi->bv_offset = 0;
+			bi->bv_len = PAGE_SIZE;
+		}
+
 		spin_lock(&sdev->stat_lock);
 		++sdev->stat.read_errors;
 		spin_unlock(&sdev->stat_lock);
-
-		/*
-		 * FIXME: allocate a new bio after a media error. I haven't
-		 * figured out how to reuse this one
-		 */
-		old_bio = sbio->bio;
-		bio = bio_kmalloc(GFP_NOFS, SCRUB_PAGES_PER_BIO);
-		if (!bio) {
-			/*
-			 * alloc failed. cancel the scrub and don't requeue
-			 * this sbio
-			 */
-			printk(KERN_ERR "btrfs scrub: allocation failure, "
-					"cancelling scrub\n");
-			atomic_inc(&sdev->dev->dev_root->fs_info->
-				   scrub_cancel_req);
-			goto out_no_enqueue;
-		}
-		sbio->bio = bio;
-		bio->bi_private = sbio;
-		bio->bi_end_io = scrub_bio_end_io;
-		bio->bi_sector = 0;
-		bio->bi_bdev = sbio->sdev->dev->bdev;
-		bio->bi_size = 0;
-		for (i = 0; i < SCRUB_PAGES_PER_BIO; ++i) {
-			struct page *page;
-			page = old_bio->bi_io_vec[i].bv_page;
-			bio_add_page(bio, page, PAGE_SIZE, 0);
-		}
-		bio_put(old_bio);
 		goto out;
 	}
 	for (i = 0; i < sbio->count; ++i) {
@@ -581,7 +455,6 @@ static void scrub_checksum(struct btrfs_work *work)
 	sbio->next_free = sdev->first_free;
 	sdev->first_free = sbio->index;
 	spin_unlock(&sdev->list_lock);
-out_no_enqueue:
 	atomic_dec(&sdev->in_flight);
 	wake_up(&sdev->list_wait);
 }