btrfs: relocation: review the call sites which can be interrupted by signal
Since most metadata reservation calls can return -EINTR when get
interrupted by fatal signal, we need to review the all the metadata
reservation call sites.
In relocation code, the metadata reservation happens in the following
sites:
- btrfs_block_rsv_refill() in merge_reloc_root()
merge_reloc_root() is a pretty critical section, we don't want to be
interrupted by signal, so change the flush status to
BTRFS_RESERVE_FLUSH_LIMIT, so it won't get interrupted by signal.
Since such change can be ENPSPC-prone, also shrink the amount of
metadata to reserve least amount avoid deadly ENOSPC there.
- btrfs_block_rsv_refill() in reserve_metadata_space()
It calls with BTRFS_RESERVE_FLUSH_LIMIT, which won't get interrupted
by signal.
- btrfs_block_rsv_refill() in prepare_to_relocate()
- btrfs_block_rsv_add() in prepare_to_relocate()
- btrfs_block_rsv_refill() in relocate_block_group()
- btrfs_delalloc_reserve_metadata() in relocate_file_extent_cluster()
- btrfs_start_transaction() in relocate_block_group()
- btrfs_start_transaction() in create_reloc_inode()
Can be interrupted by fatal signal and we can handle it easily.
For these call sites, just catch the -EINTR value in btrfs_balance()
and count them as canceled.
CC: stable@vger.kernel.org # 5.4+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index c1a4dab..537ccf6 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4135,7 +4135,22 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
mutex_lock(&fs_info->balance_mutex);
if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req))
btrfs_info(fs_info, "balance: paused");
- else if (ret == -ECANCELED && atomic_read(&fs_info->balance_cancel_req))
+ /*
+ * Balance can be canceled by:
+ *
+ * - Regular cancel request
+ * Then ret == -ECANCELED and balance_cancel_req > 0
+ *
+ * - Fatal signal to "btrfs" process
+ * Either the signal caught by wait_reserve_ticket() and callers
+ * got -EINTR, or caught by btrfs_should_cancel_balance() and
+ * got -ECANCELED.
+ * Either way, in this case balance_cancel_req = 0, and
+ * ret == -EINTR or ret == -ECANCELED.
+ *
+ * So here we only check the return value to catch canceled balance.
+ */
+ else if (ret == -ECANCELED || ret == -EINTR)
btrfs_info(fs_info, "balance: canceled");
else
btrfs_info(fs_info, "balance: ended with status: %d", ret);
