linux-kernel - Re: [PATCH v3] bcachefs: init freespace inited bits to 0 in bch2_fs

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Message-ID: <zks5hk34if64nu4t7tsnjc2om4cdyo7fs62fgyxjzetr6njo72@ajmllmpmex45>
Date: Fri, 25 Oct 2024 20:30:30 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Piotr Zalewski <pZ010001011111@...ton.me>
Cc: linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	skhan@...uxfoundation.org, syzbot+2b6a17991a6af64f9489@...kaller.appspotmail.com
Subject: Re: [PATCH v3] bcachefs: init freespace inited bits to 0 in
 bch2_fs_initialize

On Sat, Oct 26, 2024 at 12:15:49AM +0000, Piotr Zalewski wrote:
> Initialize freespace_initialized bits to 0 in member's flags and update
> member's cached version for each device in bch2_fs_initialize.
> 
> It's possible for the bits to be set to 1 before fs is initialized and if
> call to bch2_trans_mark_dev_sbs (just before bch2_fs_freespace_init) fails
> bits remain to be 1 which can later indirectly trigger BUG condition in
> bch2_bucket_alloc_freelist during shutdown.
> 
> Reported-by: syzbot+2b6a17991a6af64f9489@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2b6a17991a6af64f9489
> Fixes: bbe682c76789 ("bcachefs: Ensure devices are always correctly initialized")
> Suggested-by: Kent Overstreet <kent.overstreet@...ux.dev>
> Signed-off-by: Piotr Zalewski <pZ010001011111@...ton.me>
> ---
> 
> Notes:
>     changes in v3:
>         - v2 rebased
> 
>     changes in v2:
>         - unconditionally set freespace initialized bits to false at
>           the top of bch2_fs_initialized instead of only if
>           bch2_trans_mark_dev_sbs fails
> 
>     Link to v2: https://lore.kernel.org/linux-bcachefs/20241021174151.37692-2-pZ010001011111@proton.me/
>     Link to v1: https://lore.kernel.org/linux-bcachefs/20241020170708.67044-2-pZ010001011111@proton.me/
> 
>  fs/bcachefs/recovery.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/bcachefs/recovery.c b/fs/bcachefs/recovery.c
> index fdf2aa2ffc13..8d4c93a1f5aa 100644
> --- a/fs/bcachefs/recovery.c
> +++ b/fs/bcachefs/recovery.c
> @@ -1029,6 +1029,7 @@ int bch2_fs_initialize(struct bch_fs *c)
>  	struct bch_inode_unpacked root_inode, lostfound_inode;
>  	struct bkey_inode_buf packed_inode;
>  	struct qstr lostfound = QSTR("lost+found");
> +	struct bch_member *m;
>  	int ret;
>  
>  	bch_notice(c, "initializing new filesystem");
> @@ -1045,6 +1046,13 @@ int bch2_fs_initialize(struct bch_fs *c)
>  		SET_BCH_SB_VERSION_UPGRADE_COMPLETE(c->disk_sb.sb, bcachefs_metadata_version_current);
>  		bch2_write_super(c);
>  	}
> +
> +	for_each_member_device(c, ca) {
> +		m = bch2_members_v2_get_mut(c->disk_sb.sb, ca->dev_idx);
> +		SET_BCH_MEMBER_FREESPACE_INITIALIZED(m, false);
> +		ca->mi = bch2_mi_to_cpu(m);
> +	}
> +

I'm also adding a write_super() call here: that's what updates
ca->mi.freespace_initialized which the freespace init path will later
check.

>  	mutex_unlock(&c->sb_lock);
>  
>  	c->curr_recovery_pass = BCH_RECOVERY_PASS_NR;
> -- 
> 2.47.0
> 
>