Re: [PATCH v2 2/3] xfs: don't assert perag when free perag

["Darrick J. Wong" <djwong@kernel.org>]

On Sat, Dec 09, 2023 at 08:21:06PM +0800, Long Li wrote:
> When releasing the perag in xfs_free_perag(), the assertion that the
> perag in readix tree is correct in most cases. However, there is one
> corner case where the assertion is not true. During log recovery, the
> AGs become visible(that is included in mp->m_sb.sb_agcount) first, and
> then the perag is initialized. If the initialization of the perag fails,
> the assertion will be triggered. Worse yet, null pointer dereferencing
> can occur.
> 
> Signed-off-by: Long Li <leo.lilong@huawei.com>
> ---
>  fs/xfs/libxfs/xfs_ag.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> index cc10a3ca052f..11ed048c350c 100644
> --- a/fs/xfs/libxfs/xfs_ag.c
> +++ b/fs/xfs/libxfs/xfs_ag.c
> @@ -258,7 +258,8 @@ xfs_free_perag(
>  		spin_lock(&mp->m_perag_lock);
>  		pag = radix_tree_delete(&mp->m_perag_tree, agno);
>  		spin_unlock(&mp->m_perag_lock);
> -		ASSERT(pag);
> +		if (!pag)
> +			break;

Why wouldn't you continue to the next agnumber?

--D

>  		XFS_IS_CORRUPT(pag->pag_mount, atomic_read(&pag->pag_ref) != 0);
>  		xfs_defer_drain_free(&pag->pag_intents_drain);
>  
> -- 
> 2.31.1
> 
>