1 files changed, 35 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 63600dc2ac4c..d60b6caf09e8 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -747,6 +747,7 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
         struct btrfs_pending_snapshot *pending_snapshot;
         struct btrfs_trans_handle *trans;
         int ret;
+        bool snapshot_force_cow = false;
 
         if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
                 return -EINVAL;
@@ -763,6 +764,11 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
                 goto free_pending;
         }
 
+        /*
+         * Force new buffered writes to reserve space even when NOCOW is
+         * possible. This is to avoid later writeback (running dealloc) to
+         * fallback to COW mode and unexpectedly fail with ENOSPC.
+         */
         atomic_inc(&root->will_be_snapshotted);
         smp_mb__after_atomic();
         /* wait for no snapshot writes */
@@ -773,6 +779,14 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
         if (ret)
                 goto dec_and_free;
 
+        /*
+         * All previous writes have started writeback in NOCOW mode, so now
+         * we force future writes to fallback to COW mode during snapshot
+         * creation.
+         */
+        atomic_inc(&root->snapshot_force_cow);
+        snapshot_force_cow = true;
+
         btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
 
         btrfs_init_block_rsv(&pending_snapshot->block_rsv,
@@ -837,6 +851,8 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
 fail:
         btrfs_subvolume_release_metadata(fs_info, &pending_snapshot->block_rsv);
 dec_and_free:
+        if (snapshot_force_cow)
+                atomic_dec(&root->snapshot_force_cow);
         if (atomic_dec_and_test(&root->will_be_snapshotted))
                 wake_up_var(&root->will_be_snapshotted);
 free_pending:
@@ -3453,6 +3469,25 @@ static int btrfs_extent_same_range(struct inode *src, u64 loff, u64 olen,
 
                 same_lock_start = min_t(u64, loff, dst_loff);
                 same_lock_len = max_t(u64, loff, dst_loff) + len - same_lock_start;
+        } else {
+                /*
+                 * If the source and destination inodes are different, the
+                 * source's range end offset matches the source's i_size, that
+                 * i_size is not a multiple of the sector size, and the
+                 * destination range does not go past the destination's i_size,
+                 * we must round down the length to the nearest sector size
+                 * multiple. If we don't do this adjustment we end replacing
+                 * with zeroes the bytes in the range that starts at the
+                 * deduplication range's end offset and ends at the next sector
+                 * size multiple.
+                 */
+                if (loff + olen == i_size_read(src) &&
+                    dst_loff + len < i_size_read(dst)) {
+                        const u64 sz = BTRFS_I(src)->root->fs_info->sectorsize;
+
+                        len = round_down(i_size_read(src), sz) - loff;
+                        olen = len;
+                }
         }
 
 again: