Re: [PATCH] erofs: fix missing folio_unlock causing lock imbalance

[Gao Xiang]

Hi Zhan,

On 2026/3/31 10:33, Zhan Xusheng wrote:
> folio_trylock() in erofs_try_to_free_all_cached_folios() may
> successfully acquire the folio lock, but the subsequent check
> for erofs_folio_is_managed() can skip unlocking when the folio
> is not managed by EROFS.

Do you find some real timing?

I don't think it can really happen, because:

> This leads to a lock imbalance and leaves the folio permanently
> locked, which may cause reclaim stalls or interfere with memory
> management.
>
> Fix this by ensuring folio_unlock() is called before continuing.

If a folio links to a pcluster, folio->private will be non-NULL,
and pcl->compressed_bvecs[i] points to that folios.

And z_erofs_cache_release_folio() will be called with folio lock,
and pcl->compressed_bvecs[i] will be set NULL here.

So I don't think erofs_try_to_free_all_cached_folios() can find
!erofs_folio_is_managed(sbi, folio) in the real world.

> Signed-off-by: Zhan Xusheng <zhanxusheng@xxxxxxxxxx>
> ---
>   fs/erofs/zdata.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index fe8121df9ef2..9d7ff22f1622 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -605,8 +605,10 @@ static int erofs_try_to_free_all_cached_folios(struct erofs_sb_info *sbi,
>   			if (!folio_trylock(folio))
>   				return -EBUSY;
>   
> -			if (!erofs_folio_is_managed(sbi, folio))
> +			if (!erofs_folio_is_managed(sbi, folio)) {
> +				folio_unlock(folio);
>   				continue;
> +			}
>   			pcl->compressed_bvecs[i].page = NULL;
>   			folio_detach_private(folio);

But I admit that we should rewrite in function as:

			if (!erofs_folio_is_managed(sbi, folio)) {
				DBG_BUGON(1);
			} else {
				pcl->compressed_bvecs[i].page = NULL;
				folio_detach_private(folio);
			}
			folio_unlock(folio);

Thanks,
Gao Xiang


>   			folio_unlock(folio);