[V20,11/19] Btrfs: subpage-blocksize: Prevent writes to an extent buffer when PG_writeback flag is set
diff mbox

Message ID 1467606879-14181-12-git-send-email-chandan@linux.vnet.ibm.com
State New
Headers show

Commit Message

Chandan Rajendra July 4, 2016, 4:34 a.m. UTC
In non-subpage-blocksize scenario, BTRFS_HEADER_FLAG_WRITTEN flag
prevents Btrfs code from writing into an extent buffer whose pages are
under writeback. This facility isn't sufficient for achieving the same
in subpage-blocksize scenario, since we have more than one extent buffer
mapped to a page.

Hence this patch adds a new flag (i.e. EXTENT_BUFFER_HEAD_WRITEBACK) and
corresponding code to track the writeback status of the page and to
prevent writes to any of the extent buffers mapped to the page while
writeback is going on.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
---
 fs/btrfs/ctree.c       |  18 ++++++
 fs/btrfs/extent-tree.c |  10 ++++
 fs/btrfs/extent_io.c   | 150 ++++++++++++++++++++++++++++++++++++++++---------
 fs/btrfs/extent_io.h   |   1 +
 4 files changed, 152 insertions(+), 27 deletions(-)

Patch
diff mbox

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 4e35a21..0a56d1b 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1541,6 +1541,7 @@  noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
 		    struct extent_buffer *parent, int parent_slot,
 		    struct extent_buffer **cow_ret)
 {
+	struct extent_buffer_head *ebh = eb_head(buf);
 	u64 search_start;
 	int ret;
 
@@ -1555,6 +1556,14 @@  noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
 
 	if (!should_cow_block(trans, root, buf)) {
 		trans->dirty = true;
+		if (test_bit(EXTENT_BUFFER_HEAD_WRITEBACK, &ebh->bflags)) {
+			if (parent)
+				btrfs_set_lock_blocking(parent);
+			btrfs_set_lock_blocking(buf);
+			wait_on_bit_io(&ebh->bflags,
+				EXTENT_BUFFER_HEAD_WRITEBACK,
+				TASK_UNINTERRUPTIBLE);
+		}
 		*cow_ret = buf;
 		return 0;
 	}
@@ -2686,6 +2695,7 @@  int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
 		      *root, struct btrfs_key *key, struct btrfs_path *p, int
 		      ins_len, int cow)
 {
+	struct extent_buffer_head *ebh;
 	struct extent_buffer *b;
 	int slot;
 	int ret;
@@ -2790,6 +2800,14 @@  again:
 			 */
 			if (!should_cow_block(trans, root, b)) {
 				trans->dirty = true;
+				ebh = eb_head(b);
+				if (test_bit(EXTENT_BUFFER_HEAD_WRITEBACK,
+						&ebh->bflags)) {
+					btrfs_set_path_blocking(p);
+					wait_on_bit_io(&ebh->bflags,
+						EXTENT_BUFFER_HEAD_WRITEBACK,
+						TASK_UNINTERRUPTIBLE);
+				}
 				goto cow_done;
 			}
 
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 590d0e7..4ead0ff 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8224,15 +8224,25 @@  static struct extent_buffer *
 btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		      u64 bytenr, int level)
 {
+	struct extent_buffer_head *ebh;
 	struct extent_buffer *buf;
 
 	buf = btrfs_find_create_tree_block(root, bytenr, root->nodesize);
 	if (IS_ERR(buf))
 		return buf;
 
+	ebh = eb_head(buf);
 	btrfs_set_header_generation(buf, trans->transid);
 	btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
 	btrfs_tree_lock(buf);
+
+	if (test_bit(EXTENT_BUFFER_HEAD_WRITEBACK,
+			&ebh->bflags)) {
+		btrfs_set_lock_blocking(buf);
+		wait_on_bit_io(&ebh->bflags, EXTENT_BUFFER_HEAD_WRITEBACK,
+			TASK_UNINTERRUPTIBLE);
+	}
+
 	clean_tree_block(trans, root->fs_info, buf);
 	clear_bit(EXTENT_BUFFER_STALE, &buf->ebflags);
 
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 694d2dc..0bdb27d 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3725,6 +3725,52 @@  void wait_on_extent_buffer_writeback(struct extent_buffer *eb)
 		    TASK_UNINTERRUPTIBLE);
 }
 
+static void lock_extent_buffers(struct extent_buffer_head *ebh,
+				struct extent_page_data *epd)
+{
+	struct extent_buffer *locked_eb = NULL;
+	struct extent_buffer *eb;
+again:
+	eb = &ebh->eb;
+	do {
+		if (eb == locked_eb)
+			continue;
+
+		if (!btrfs_try_tree_write_lock(eb))
+			goto backoff;
+
+	} while ((eb = eb->eb_next) != NULL);
+
+	return;
+
+backoff:
+	if (locked_eb && (locked_eb->start > eb->start))
+		btrfs_tree_unlock(locked_eb);
+
+	locked_eb = eb;
+
+	eb = &ebh->eb;
+	while (eb != locked_eb) {
+		btrfs_tree_unlock(eb);
+		eb = eb->eb_next;
+	}
+
+	flush_write_bio(epd);
+
+	btrfs_tree_lock(locked_eb);
+
+	goto again;
+}
+
+static void unlock_extent_buffers(struct extent_buffer_head *ebh)
+{
+	struct extent_buffer *eb = &ebh->eb;
+
+	do {
+		btrfs_tree_unlock(eb);
+	} while ((eb = eb->eb_next) != NULL);
+}
+
 static void lock_extent_buffer_pages(struct extent_buffer_head *ebh,
 				struct extent_page_data *epd)
 {
@@ -3744,21 +3790,17 @@  static void lock_extent_buffer_pages(struct extent_buffer_head *ebh,
 }
 
 static int noinline_for_stack
-lock_extent_buffer_for_io(struct extent_buffer *eb,
+mark_extent_buffer_writeback(struct extent_buffer *eb,
 			struct btrfs_fs_info *fs_info,
 			struct extent_page_data *epd)
 {
+	struct extent_buffer_head *ebh = eb_head(eb);
+	struct extent_buffer *cur;
 	int dirty;
 	int ret = 0;
 
-	if (!btrfs_try_tree_write_lock(eb)) {
-		flush_write_bio(epd);
-		btrfs_tree_lock(eb);
-	}
-
 	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->ebflags)) {
 		dirty = test_bit(EXTENT_BUFFER_DIRTY, &eb->ebflags);
-		btrfs_tree_unlock(eb);
 		if (!epd->sync_io) {
 			if (!dirty)
 				return 1;
@@ -3766,15 +3808,23 @@  lock_extent_buffer_for_io(struct extent_buffer *eb,
 				return 2;
 		}
 
+		cur = &ebh->eb;
+		do {
+			btrfs_set_lock_blocking(cur);
+		} while ((cur = cur->eb_next) != NULL);
+
 		flush_write_bio(epd);
 
 		while (1) {
 			wait_on_extent_buffer_writeback(eb);
-			btrfs_tree_lock(eb);
 			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->ebflags))
 				break;
-			btrfs_tree_unlock(eb);
 		}
+
+		cur = &ebh->eb;
+		do {
+			btrfs_clear_lock_blocking(cur);
+		} while ((cur = cur->eb_next) != NULL);
 	}
 
 	/*
@@ -3782,22 +3832,20 @@  lock_extent_buffer_for_io(struct extent_buffer *eb,
 	 * under IO since we can end up having no IO bits set for a short period
 	 * of time.
 	 */
-	spin_lock(&eb_head(eb)->refs_lock);
+	spin_lock(&ebh->refs_lock);
 	if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->ebflags)) {
 		set_bit(EXTENT_BUFFER_WRITEBACK, &eb->ebflags);
-		spin_unlock(&eb_head(eb)->refs_lock);
+		spin_unlock(&ebh->refs_lock);
 		btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
 		__percpu_counter_add(&fs_info->dirty_metadata_bytes,
 				     -eb->len,
 				     fs_info->dirty_metadata_batch);
 		ret = 0;
 	} else {
-		spin_unlock(&eb_head(eb)->refs_lock);
+		spin_unlock(&ebh->refs_lock);
 		ret = 1;
 	}
 
-	btrfs_tree_unlock(eb);
-
 	return ret;
 }
 
@@ -3947,8 +3995,8 @@  static void set_btree_ioerr(struct extent_buffer *eb, struct page *page)
 
 static void end_bio_subpagesize_blocksize_ebh_writepage(struct bio *bio)
 {
-	struct bio_vec *bvec;
 	struct extent_buffer *eb;
+	struct bio_vec *bvec;
 	int i, done;
 
 	bio_for_each_segment_all(bvec, bio, i) {
@@ -3980,6 +4028,15 @@  static void end_bio_subpagesize_blocksize_ebh_writepage(struct bio *bio)
 
 			end_extent_buffer_writeback(eb);
 
+			if (done) {
+				struct extent_buffer_head *ebh = eb_head(eb);
+
+				clear_bit(EXTENT_BUFFER_HEAD_WRITEBACK,
+					&ebh->bflags);
+				smp_mb__after_atomic();
+				wake_up_bit(&ebh->bflags,
+					EXTENT_BUFFER_HEAD_WRITEBACK);
+			}
 		} while ((eb = eb->eb_next) != NULL);
 
 	}
@@ -3989,6 +4046,7 @@  static void end_bio_subpagesize_blocksize_ebh_writepage(struct bio *bio)
 
 static void end_bio_regular_ebh_writepage(struct bio *bio)
 {
+	struct extent_buffer_head *ebh;
 	struct extent_buffer *eb;
 	struct bio_vec *bvec;
 	int i, done;
@@ -3999,7 +4057,9 @@  static void end_bio_regular_ebh_writepage(struct bio *bio)
 		eb = (struct extent_buffer *)page->private;
 		BUG_ON(!eb);
 
-		done = atomic_dec_and_test(&eb_head(eb)->io_bvecs);
+		ebh = eb_head(eb);
+
+		done = atomic_dec_and_test(&ebh->io_bvecs);
 
 		if (bio->bi_error ||
 		    test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->ebflags)) {
@@ -4013,6 +4073,10 @@  static void end_bio_regular_ebh_writepage(struct bio *bio)
 			continue;
 
 		end_extent_buffer_writeback(eb);
+
+		clear_bit(EXTENT_BUFFER_HEAD_WRITEBACK, &ebh->bflags);
+		smp_mb__after_atomic();
+		wake_up_bit(&ebh->bflags, EXTENT_BUFFER_HEAD_WRITEBACK);
 	}
 
 	bio_put(bio);
@@ -4054,8 +4118,14 @@  write_regular_ebh(struct extent_buffer_head *ebh,
 			set_btree_ioerr(eb, p);
 			end_page_writeback(p);
 			if (atomic_sub_and_test(num_pages - i,
-							&eb_head(eb)->io_bvecs))
+							&ebh->io_bvecs)) {
 				end_extent_buffer_writeback(eb);
+				clear_bit(EXTENT_BUFFER_HEAD_WRITEBACK,
+					&ebh->bflags);
+				smp_mb__after_atomic();
+				wake_up_bit(&ebh->bflags,
+					EXTENT_BUFFER_HEAD_WRITEBACK);
+			}
 			ret = -EIO;
 			break;
 		}
@@ -4089,6 +4159,7 @@  static int write_subpagesize_blocksize_ebh(struct extent_buffer_head *ebh,
 	unsigned long i;
 	unsigned long bio_flags = 0;
 	int rw = (epd->sync_io ? WRITE_SYNC : WRITE) | REQ_META;
+	int nr_eb_submitted = 0;
 	int ret = 0, err = 0;
 
 	eb = &ebh->eb;
@@ -4101,7 +4172,7 @@  static int write_subpagesize_blocksize_ebh(struct extent_buffer_head *ebh,
 			continue;
 
 		clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->ebflags);
-		atomic_inc(&eb_head(eb)->io_bvecs);
+		atomic_inc(&ebh->io_bvecs);
 
 		if (btrfs_header_owner(eb) == BTRFS_TREE_LOG_OBJECTID)
 			bio_flags = EXTENT_BIO_TREE_LOG;
@@ -4119,6 +4190,8 @@  static int write_subpagesize_blocksize_ebh(struct extent_buffer_head *ebh,
 			atomic_dec(&eb_head(eb)->io_bvecs);
 			end_extent_buffer_writeback(eb);
 			err = -EIO;
+		} else {
+			++nr_eb_submitted;
 		}
 	} while ((eb = eb->eb_next) != NULL);
 
@@ -4126,6 +4199,12 @@  static int write_subpagesize_blocksize_ebh(struct extent_buffer_head *ebh,
 		update_nr_written(p, wbc, 1);
 	}
 
+	if (!nr_eb_submitted) {
+		clear_bit(EXTENT_BUFFER_HEAD_WRITEBACK, &ebh->bflags);
+		smp_mb__after_atomic();
+		wake_up_bit(&ebh->bflags, EXTENT_BUFFER_HEAD_WRITEBACK);
+	}
+
 	unlock_page(p);
 
 	return ret;
@@ -4237,24 +4316,31 @@  retry:
 
 			j = 0;
 			ebs_to_write = dirty_ebs = 0;
+
+			lock_extent_buffers(ebh, &epd);
+
+			set_bit(EXTENT_BUFFER_HEAD_WRITEBACK, &ebh->bflags);
+
 			eb = &ebh->eb;
 			do {
 				BUG_ON(j >= BITS_PER_LONG);
 
-				ret = lock_extent_buffer_for_io(eb, fs_info, &epd);
+				ret = mark_extent_buffer_writeback(eb, fs_info,
+								&epd);
 				switch (ret) {
 				case 0:
 					/*
-					  EXTENT_BUFFER_DIRTY was set and we were able to
-					  clear it.
+					  EXTENT_BUFFER_DIRTY was set and we were
+					  able to clear it.
 					*/
 					set_bit(j, &ebs_to_write);
 					break;
 				case 2:
 					/*
-					  EXTENT_BUFFER_DIRTY was set, but we were unable
-					  to clear EXTENT_BUFFER_WRITEBACK that was set
-					  before we got the extent buffer locked.
+					  EXTENT_BUFFER_DIRTY was set, but we were
+					  unable to clear EXTENT_BUFFER_WRITEBACK
+					  that was set before we got the extent
+					  buffer locked.
 					 */
 					set_bit(j, &dirty_ebs);
 				default:
@@ -4268,22 +4354,32 @@  retry:
 
 			ret = 0;
 
+			unlock_extent_buffers(ebh);
+
 			if (!ebs_to_write) {
+				clear_bit(EXTENT_BUFFER_HEAD_WRITEBACK,
+					&ebh->bflags);
+				smp_mb__after_atomic();
+				wake_up_bit(&ebh->bflags,
+					EXTENT_BUFFER_HEAD_WRITEBACK);
 				free_extent_buffer(&ebh->eb);
 				continue;
 			}
 
 			/*
-			  Now that we know that atleast one of the extent buffer
+			  Now that we know that atleast one of the extent buffers
 			  belonging to the extent buffer head must be written to
 			  the disk, lock the extent_buffer_head's pages.
 			 */
 			lock_extent_buffer_pages(ebh, &epd);
 
 			if (ebh->eb.len < PAGE_SIZE) {
-				ret = write_subpagesize_blocksize_ebh(ebh, fs_info, wbc, &epd, ebs_to_write);
+				ret = write_subpagesize_blocksize_ebh(ebh, fs_info,
+								wbc, &epd,
+								ebs_to_write);
 				if (dirty_ebs) {
-					redirty_extent_buffer_pages_for_writepage(&ebh->eb, wbc);
+					redirty_extent_buffer_pages_for_writepage(&ebh->eb,
+										wbc);
 				}
 			} else {
 				ret = write_regular_ebh(ebh, fs_info, wbc, &epd);
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 2ea8451..e8e504c 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -35,6 +35,7 @@ 
 #define EXTENT_BUFFER_HEAD_TREE_REF 0
 #define EXTENT_BUFFER_HEAD_DUMMY 1
 #define EXTENT_BUFFER_HEAD_IN_TREE 2
+#define EXTENT_BUFFER_HEAD_WRITEBACK 3
 
 /* these are bit numbers for test/set bit on extent buffer */
 #define EXTENT_BUFFER_UPTODATE 0