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Date:   Thu, 13 Feb 2020 20:13:39 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     dsterba@...e.cz, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Subject: Re: [PATCH 4.9 083/116] btrfs: free block groups after freeing fs
 trees

On Thu, Feb 13, 2020 at 09:55:33PM +0100, David Sterba wrote:
>On Thu, Feb 13, 2020 at 07:20:27AM -0800, Greg Kroah-Hartman wrote:
>> From: Josef Bacik <josef@...icpanda.com>
>>
>> [ Upstream commit 4e19443da1941050b346f8fc4c368aa68413bc88 ]
>>
>> Sometimes when running generic/475 we would trip the
>> WARN_ON(cache->reserved) check when free'ing the block groups on umount.
>> This is because sometimes we don't commit the transaction because of IO
>> errors and thus do not cleanup the tree logs until at umount time.
>>
>> These blocks are still reserved until they are cleaned up, but they
>> aren't cleaned up until _after_ we do the free block groups work.  Fix
>> this by moving the free after free'ing the fs roots, that way all of the
>> tree logs are cleaned up and we have a properly cleaned fs.  A bunch of
>> loops of generic/475 confirmed this fixes the problem.
>>
>> CC: stable@...r.kernel.org # 4.9+
>> Signed-off-by: Josef Bacik <josef@...icpanda.com>
>> Reviewed-by: David Sterba <dsterba@...e.com>
>> Signed-off-by: David Sterba <dsterba@...e.com>
>> Signed-off-by: Sasha Levin <sashal@...nel.org>
>> ---
>>  fs/btrfs/disk-io.c | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index eab5a9065f093..439b5f5dc3274 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -3864,6 +3864,15 @@ void close_ctree(struct btrfs_root *root)
>>  	clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
>>  	free_root_pointers(fs_info, true);
>>
>> +	/*
>> +	 * We must free the block groups after dropping the fs_roots as we could
>> +	 * have had an IO error and have left over tree log blocks that aren't
>> +	 * cleaned up until the fs roots are freed.  This makes the block group
>> +	 * accounting appear to be wrong because there's pending reserved bytes,
>> +	 * so make sure we do the block group cleanup afterwards.
>> +	 */
>> +	btrfs_free_block_groups(fs_info);
>
>Something's wrong here.  The patch 4e19443da1 moves the
>btrfs_free_block_groups() call and the stable backport lacks the "-"
>line. However the patch applies cleanly on 4.9.213.
>
>3855         btrfs_free_block_groups(fs_info);
>^^^^
>
>3856
>3857         /*
>3858          * we must make sure there is not any read request to
>3859          * submit after we stopping all workers.
>3860          */
>3861         invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
>3862         btrfs_stop_all_workers(fs_info);
>3863
>3864         clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
>3865         free_root_pointers(fs_info, 1);
>3866
>3867         /*
>3868          * We must free the block groups after dropping the fs_roots as we could
>3869          * have had an IO error and have left over tree log blocks that aren't
>3870          * cleaned up until the fs roots are freed.  This makes the block group
>3871          * accounting appear to be wrong because there's pending reserved bytes,
>3872          * so make sure we do the block group cleanup afterwards.
>3873          */
>3874         btrfs_free_block_groups(fs_info);
>
>The first one should not be there.

Sigh, sorry about that. The story behind this is that for this patch to
apply, we first must have 5cdd7db6c5c9 ("Btrfs: fix assertion failure
when freeing block groups at close_ctree()") which moves the
btrfs_free_block_groups() call to line 3863 in your code above.

I somehow goofed up picking it up and (probably) messed up the rebase
when it went missing, sorry again.

I'll fix it up for the next release.

-- 
Thanks,
Sasha

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