Btrfs: implement repair function when direct read fails

This patch implement data repair function when direct read fails.

The detail of the implementation is:
- When we find the data is not right, we try to read the data from the other
  mirror.
- When the io on the mirror ends, we will insert the endio work into the
  dedicated btrfs workqueue, not common read endio workqueue, because the
  original endio work is still blocked in the btrfs endio workqueue, if we
  insert the endio work of the io on the mirror into that workqueue, deadlock
  would happen.
- After we get right data, we write it back to the corrupted mirror.
- And if the data on the new mirror is still corrupted, we will try next
  mirror until we read right data or all the mirrors are traversed.
- After the above work, we set the uptodate flag according to the result.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 255 insertions, 21 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 09d8c5e..c3c3269 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7242,30 +7242,267 @@ unlock_err:
 	return ret;
 }
 
-static int btrfs_subio_endio_read(struct inode *inode,
-				  struct btrfs_io_bio *io_bio)
+static inline int submit_dio_repair_bio(struct inode *inode, struct bio *bio,
+					int rw, int mirror_num)
+{
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	int ret;
+
+	BUG_ON(rw & REQ_WRITE);
+
+	bio_get(bio);
+
+	ret = btrfs_bio_wq_end_io(root->fs_info, bio,
+				  BTRFS_WQ_ENDIO_DIO_REPAIR);
+	if (ret)
+		goto err;
+
+	ret = btrfs_map_bio(root, rw, bio, mirror_num, 0);
+err:
+	bio_put(bio);
+	return ret;
+}
+
+static int btrfs_check_dio_repairable(struct inode *inode,
+				      struct bio *failed_bio,
+				      struct io_failure_record *failrec,
+				      int failed_mirror)
+{
+	int num_copies;
+
+	num_copies = btrfs_num_copies(BTRFS_I(inode)->root->fs_info,
+				      failrec->logical, failrec->len);
+	if (num_copies == 1) {
+		/*
+		 * we only have a single copy of the data, so don't bother with
+		 * all the retry and error correction code that follows. no
+		 * matter what the error is, it is very likely to persist.
+		 */
+		pr_debug("Check DIO Repairable: cannot repair, num_copies=%d, next_mirror %d, failed_mirror %d\n",
+			 num_copies, failrec->this_mirror, failed_mirror);
+		return 0;
+	}
+
+	failrec->failed_mirror = failed_mirror;
+	failrec->this_mirror++;
+	if (failrec->this_mirror == failed_mirror)
+		failrec->this_mirror++;
+
+	if (failrec->this_mirror > num_copies) {
+		pr_debug("Check DIO Repairable: (fail) num_copies=%d, next_mirror %d, failed_mirror %d\n",
+			 num_copies, failrec->this_mirror, failed_mirror);
+		return 0;
+	}
+
+	return 1;
+}
+
+static int dio_read_error(struct inode *inode, struct bio *failed_bio,
+			  struct page *page, u64 start, u64 end,
+			  int failed_mirror, bio_end_io_t *repair_endio,
+			  void *repair_arg)
+{
+	struct io_failure_record *failrec;
+	struct bio *bio;
+	int isector;
+	int read_mode;
+	int ret;
+
+	BUG_ON(failed_bio->bi_rw & REQ_WRITE);
+
+	ret = btrfs_get_io_failure_record(inode, start, end, &failrec);
+	if (ret)
+		return ret;
+
+	ret = btrfs_check_dio_repairable(inode, failed_bio, failrec,
+					 failed_mirror);
+	if (!ret) {
+		free_io_failure(inode, failrec);
+		return -EIO;
+	}
+
+	if (failed_bio->bi_vcnt > 1)
+		read_mode = READ_SYNC | REQ_FAILFAST_DEV;
+	else
+		read_mode = READ_SYNC;
+
+	isector = start - btrfs_io_bio(failed_bio)->logical;
+	isector >>= inode->i_sb->s_blocksize_bits;
+	bio = btrfs_create_repair_bio(inode, failed_bio, failrec, page,
+				      0, isector, repair_endio, repair_arg);
+	if (!bio) {
+		free_io_failure(inode, failrec);
+		return -EIO;
+	}
+
+	btrfs_debug(BTRFS_I(inode)->root->fs_info,
+		    "Repair DIO Read Error: submitting new dio read[%#x] to this_mirror=%d, in_validation=%d\n",
+		    read_mode, failrec->this_mirror, failrec->in_validation);
+
+	ret = submit_dio_repair_bio(inode, bio, read_mode,
+				    failrec->this_mirror);
+	if (ret) {
+		free_io_failure(inode, failrec);
+		bio_put(bio);
+	}
+
+	return ret;
+}
+
+struct btrfs_retry_complete {
+	struct completion done;
+	struct inode *inode;
+	u64 start;
+	int uptodate;
+};
+
+static void btrfs_retry_endio_nocsum(struct bio *bio, int err)
+{
+	struct btrfs_retry_complete *done = bio->bi_private;
+	struct bio_vec *bvec;
+	int i;
+
+	if (err)
+		goto end;
+
+	done->uptodate = 1;
+	bio_for_each_segment_all(bvec, bio, i)
+		clean_io_failure(done->inode, done->start, bvec->bv_page, 0);
+end:
+	complete(&done->done);
+	bio_put(bio);
+}
+
+static int __btrfs_correct_data_nocsum(struct inode *inode,
+				       struct btrfs_io_bio *io_bio)
 {
 	struct bio_vec *bvec;
+	struct btrfs_retry_complete done;
 	u64 start;
 	int i;
 	int ret;
-	int err = 0;
 
-	if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
-		return 0;
+	start = io_bio->logical;
+	done.inode = inode;
+
+	bio_for_each_segment_all(bvec, &io_bio->bio, i) {
+try_again:
+		done.uptodate = 0;
+		done.start = start;
+		init_completion(&done.done);
+
+		ret = dio_read_error(inode, &io_bio->bio, bvec->bv_page, start,
+				     start + bvec->bv_len - 1,
+				     io_bio->mirror_num,
+				     btrfs_retry_endio_nocsum, &done);
+		if (ret)
+			return ret;
+
+		wait_for_completion(&done.done);
+
+		if (!done.uptodate) {
+			/* We might have another mirror, so try again */
+			goto try_again;
+		}
+
+		start += bvec->bv_len;
+	}
+
+	return 0;
+}
+
+static void btrfs_retry_endio(struct bio *bio, int err)
+{
+	struct btrfs_retry_complete *done = bio->bi_private;
+	struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
+	struct bio_vec *bvec;
+	int uptodate;
+	int ret;
+	int i;
+
+	if (err)
+		goto end;
+
+	uptodate = 1;
+	bio_for_each_segment_all(bvec, bio, i) {
+		ret = __readpage_endio_check(done->inode, io_bio, i,
+					     bvec->bv_page, 0,
+					     done->start, bvec->bv_len);
+		if (!ret)
+			clean_io_failure(done->inode, done->start,
+					 bvec->bv_page, 0);
+		else
+			uptodate = 0;
+	}
+
+	done->uptodate = uptodate;
+end:
+	complete(&done->done);
+	bio_put(bio);
+}
 
+static int __btrfs_subio_endio_read(struct inode *inode,
+				    struct btrfs_io_bio *io_bio, int err)
+{
+	struct bio_vec *bvec;
+	struct btrfs_retry_complete done;
+	u64 start;
+	u64 offset = 0;
+	int i;
+	int ret;
+
+	err = 0;
 	start = io_bio->logical;
+	done.inode = inode;
+
 	bio_for_each_segment_all(bvec, &io_bio->bio, i) {
 		ret = __readpage_endio_check(inode, io_bio, i, bvec->bv_page,
 					     0, start, bvec->bv_len);
-		if (ret)
-			err = -EIO;
+		if (likely(!ret))
+			goto next;
+try_again:
+		done.uptodate = 0;
+		done.start = start;
+		init_completion(&done.done);
+
+		ret = dio_read_error(inode, &io_bio->bio, bvec->bv_page, start,
+				     start + bvec->bv_len - 1,
+				     io_bio->mirror_num,
+				     btrfs_retry_endio, &done);
+		if (ret) {
+			err = ret;
+			goto next;
+		}
+
+		wait_for_completion(&done.done);
+
+		if (!done.uptodate) {
+			/* We might have another mirror, so try again */
+			goto try_again;
+		}
+next:
+		offset += bvec->bv_len;
 		start += bvec->bv_len;
 	}
 
 	return err;
 }
 
+static int btrfs_subio_endio_read(struct inode *inode,
+				  struct btrfs_io_bio *io_bio, int err)
+{
+	bool skip_csum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;
+
+	if (skip_csum) {
+		if (unlikely(err))
+			return __btrfs_correct_data_nocsum(inode, io_bio);
+		else
+			return 0;
+	} else {
+		return __btrfs_subio_endio_read(inode, io_bio, err);
+	}
+}
+
 static void btrfs_endio_direct_read(struct bio *bio, int err)
 {
 	struct btrfs_dio_private *dip = bio->bi_private;
@@ -7273,8 +7510,8 @@ static void btrfs_endio_direct_read(struct bio *bio, int err)
 	struct bio *dio_bio;
 	struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
 
-	if (!err && (dip->flags & BTRFS_DIO_ORIG_BIO_SUBMITTED))
-		err = btrfs_subio_endio_read(inode, io_bio);
+	if (dip->flags & BTRFS_DIO_ORIG_BIO_SUBMITTED)
+		err = btrfs_subio_endio_read(inode, io_bio, err);
 
 	unlock_extent(&BTRFS_I(inode)->io_tree, dip->logical_offset,
 		      dip->logical_offset + dip->bytes - 1);
@@ -7353,19 +7590,16 @@ static int __btrfs_submit_bio_start_direct_io(struct inode *inode, int rw,
 static void btrfs_end_dio_bio(struct bio *bio, int err)
 {
 	struct btrfs_dio_private *dip = bio->bi_private;
-	int ret;
 
-	if (err) {
-		btrfs_err(BTRFS_I(dip->inode)->root->fs_info,
-			  "direct IO failed ino %llu rw %lu sector %#Lx len %u err no %d",
-		      btrfs_ino(dip->inode), bio->bi_rw,
-		      (unsigned long long)bio->bi_iter.bi_sector,
-		      bio->bi_iter.bi_size, err);
-	} else if (dip->subio_endio) {
-		ret = dip->subio_endio(dip->inode, btrfs_io_bio(bio));
-		if (ret)
-			err = ret;
-	}
+	if (err)
+		btrfs_warn(BTRFS_I(dip->inode)->root->fs_info,
+			   "direct IO failed ino %llu rw %lu sector %#Lx len %u err no %d",
+			   btrfs_ino(dip->inode), bio->bi_rw,
+			   (unsigned long long)bio->bi_iter.bi_sector,
+			   bio->bi_iter.bi_size, err);
+
+	if (dip->subio_endio)
+		err = dip->subio_endio(dip->inode, btrfs_io_bio(bio), err);
 
 	if (err) {
 		dip->errors = 1;