Re: [PATCH v2 2/2] btrfs: fix min reserved size calculation in merge_reloc_root

[Nikolay Borisov <nborisov@suse.com>]

On 26.10.20 г. 22:57 ч., Josef Bacik wrote:
> The minimum reserve size was adjusted to take into account the height of
> the tree we are merging, however we can have a root with a level == 0.
> What we want is root_level + 1 to get the number of nodes we may have to
> cow.  This fixes the enospc_debug warning pops with btrfs/101.
> 
> 44d354abf33e ("btrfs: relocation: review the call sites which can be interrupted by signal")
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

FWIW this fixes failures on btrfs/060 btrfs/062 btrfs/063 and btrfs/195 That I was seeing, the call trace was: 

[ 3680.515564] ------------[ cut here ]------------
[ 3680.515566] BTRFS: block rsv returned -28
[ 3680.515585] WARNING: CPU: 2 PID: 8339 at fs/btrfs/block-rsv.c:521 btrfs_use_block_rsv+0x162/0x180
[ 3680.515587] Modules linked in:
[ 3680.515591] CPU: 2 PID: 8339 Comm: btrfs Tainted: G        W         5.9.0-rc8-default #95
[ 3680.515593] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
[ 3680.515595] RIP: 0010:btrfs_use_block_rsv+0x162/0x180
[ 3680.515600] RSP: 0018:ffffa01ac9753910 EFLAGS: 00010282
[ 3680.515602] RAX: 0000000000000000 RBX: ffff984b34200000 RCX: 0000000000000027
[ 3680.515604] RDX: 0000000000000027 RSI: 0000000000000000 RDI: ffff984b3bd19e28
[ 3680.515606] RBP: 0000000000004000 R08: ffff984b3bd19e20 R09: 0000000000000001
[ 3680.515608] R10: 0000000000000004 R11: 0000000000000046 R12: ffff984b264fdc00
[ 3680.515609] R13: ffff984b13149000 R14: 00000000ffffffe4 R15: ffff984b34200000
[ 3680.515613] FS:  00007f4e2912b8c0(0000) GS:ffff984b3bd00000(0000) knlGS:0000000000000000
[ 3680.515615] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3680.515617] CR2: 00007fab87122150 CR3: 0000000118e42000 CR4: 00000000000006e0
[ 3680.515620] Call Trace:
[ 3680.515627]  btrfs_alloc_tree_block+0x8b/0x340
[ 3680.515633]  ? __lock_acquire+0x51a/0xac0
[ 3680.515646]  alloc_tree_block_no_bg_flush+0x4f/0x60
[ 3680.515651]  __btrfs_cow_block+0x14e/0x7e0
[ 3680.515662]  btrfs_cow_block+0x144/0x2c0
[ 3680.515670]  merge_reloc_root+0x4d4/0x610
[ 3680.515675]  ? btrfs_lookup_fs_root+0x78/0x90
[ 3680.515686]  merge_reloc_roots+0xee/0x280
[ 3680.515695]  relocate_block_group+0x2ce/0x5e0
[ 3680.515704]  btrfs_relocate_block_group+0x16e/0x310
[ 3680.515711]  btrfs_relocate_chunk+0x38/0xf0
[ 3680.515716]  btrfs_shrink_device+0x200/0x560
[ 3680.515728]  btrfs_rm_device+0x1ae/0x6a6
[ 3680.515744]  ? _copy_from_user+0x6e/0xb0
[ 3680.515750]  btrfs_ioctl+0x1afe/0x28c0
[ 3680.515755]  ? find_held_lock+0x2b/0x80
[ 3680.515760]  ? do_user_addr_fault+0x1f8/0x418
[ 3680.515773]  ? __x64_sys_ioctl+0x77/0xb0
[ 3680.515775]  __x64_sys_ioctl+0x77/0xb0
[ 3680.515781]  do_syscall_64+0x31/0x70
[ 3680.515785]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Tested-by: Nikolay Borisov <nborisov@suse.com>


> ---
>  fs/btrfs/relocation.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 3602806d71bd..9ba92d86da0b 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -1648,6 +1648,7 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc,
>  	struct btrfs_root_item *root_item;
>  	struct btrfs_path *path;
>  	struct extent_buffer *leaf;
> +	int reserve_level;
>  	int level;
>  	int max_level;
>  	int replaced = 0;
> @@ -1696,7 +1697,8 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc,
>  	 * Thus the needed metadata size is at most root_level * nodesize,
>  	 * and * 2 since we have two trees to COW.
>  	 */
> -	min_reserved = fs_info->nodesize * btrfs_root_level(root_item) * 2;
> +	reserve_level = max_t(int, 1, btrfs_root_level(root_item));
> +	min_reserved = fs_info->nodesize * reserve_level * 2;
>  	memset(&next_key, 0, sizeof(next_key));
>  
>  	while (1) {
>