The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 5a8067c0d17feb7579db0476191417b441a8996e Mon Sep 17 00:00:00 2001
From: Filipe Manana fdmanana@suse.com Date: Mon, 19 Nov 2018 09:48:12 +0000 Subject: [PATCH] Btrfs: fix access to available allocation bits when starting balance
The available allocation bits members from struct btrfs_fs_info are protected by a sequence lock, and when starting balance we access them incorrectly in two different ways:
1) In the read sequence lock loop at btrfs_balance() we use the values we read from fs_info->avail_*_alloc_bits and we can immediately do actions that have side effects and can not be undone (printing a message and jumping to a label). This is wrong because a retry might be needed, so our actions must not have side effects and must be repeatable as long as read_seqretry() returns a non-zero value. In other words, we were essentially ignoring the sequence lock;
2) Right below the read sequence lock loop, we were reading the values from avail_metadata_alloc_bits and avail_data_alloc_bits without any protection from concurrent writers, that is, reading them outside of the read sequence lock critical section.
So fix this by making sure we only read the available allocation bits while in a read sequence lock critical section and that what we do in the critical section is repeatable (has nothing that can not be undone) so that any eventual retry that is needed is handled properly.
Fixes: de98ced9e743 ("Btrfs: use seqlock to protect fs_info->avail_{data, metadata, system}_alloc_bits") Fixes: 14506127979a ("btrfs: fix a bogus warning when converting only data or metadata") Reviewed-by: Nikolay Borisov nborisov@suse.com Signed-off-by: Filipe Manana fdmanana@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 a89596c3de56..2ebc827bed88 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -3938,6 +3938,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, int ret; u64 num_devices; unsigned seq; + bool reducing_integrity;
if (btrfs_fs_closing(fs_info) || atomic_read(&fs_info->balance_pause_req) || @@ -4017,24 +4018,30 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, !(bctl->sys.target & allowed)) || ((bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) && (fs_info->avail_metadata_alloc_bits & allowed) && - !(bctl->meta.target & allowed))) { - if (bctl->flags & BTRFS_BALANCE_FORCE) { - btrfs_info(fs_info, - "balance: force reducing metadata integrity"); - } else { - btrfs_err(fs_info, - "balance: reduces metadata integrity, use --force if you want this"); - ret = -EINVAL; - goto out; - } - } + !(bctl->meta.target & allowed))) + reducing_integrity = true; + else + reducing_integrity = false; + + /* if we're not converting, the target field is uninitialized */ + meta_target = (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) ? + bctl->meta.target : fs_info->avail_metadata_alloc_bits; + data_target = (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) ? + bctl->data.target : fs_info->avail_data_alloc_bits; } while (read_seqretry(&fs_info->profiles_lock, seq));
- /* if we're not converting, the target field is uninitialized */ - meta_target = (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) ? - bctl->meta.target : fs_info->avail_metadata_alloc_bits; - data_target = (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) ? - bctl->data.target : fs_info->avail_data_alloc_bits; + if (reducing_integrity) { + if (bctl->flags & BTRFS_BALANCE_FORCE) { + btrfs_info(fs_info, + "balance: force reducing metadata integrity"); + } else { + btrfs_err(fs_info, + "balance: reduces metadata integrity, use --force if you want this"); + ret = -EINVAL; + goto out; + } + } + if (btrfs_get_num_tolerated_disk_barrier_failures(meta_target) < btrfs_get_num_tolerated_disk_barrier_failures(data_target)) { int meta_index = btrfs_bg_flags_to_raid_index(meta_target);