Re: [PATCH] erofs: use GFP_NOIO in endio decompression path of erofs

[Gao Xiang]

Hi Jiucheng,

On 2026/3/11 15:22, Jiucheng Xu via B4 Relay wrote:
> From: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>
>
> The endio decompression path of erofs calls vm_map_ram(). Due to


updated subject:

erofs: add GFP_NOIO in the bio completion if needed

The bio completion path in the process context (e.g. dm-verity)
will directly call into decompression rather than trigger another
workqueue context for minimal scheduling latencies, which can
then call vm_map_ram() with GFP_KERNEL.

Due to insufficient memory, ...

> insufficient memory, this function may generate memory swapping I/O,
> which can cause submit_bio_wait to deadlock in some scenarios.
>
> Trimmed down the call stack, as follows:
>
> f2fs_submit_read_io
>    submit_bio                      //bio_list is initialized.
>      mmc_blk_mq_recovery
>        z_erofs_endio
>          vm_map_ram
>            __pte_alloc_kernel
>              __alloc_pages_direct_reclaim
>                shrink_folio_list
>                  __swap_writepage
>                    submit_bio_wait  //bio_list is non-NULL, hang!!!
>
> Use memalloc_noio_{save,restore}() to wrap up this path.
>
> Signed-off-by: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

You can send a v2 to refine the subject and commit message.

Thanks,
Gao Xiang

> ---
>   fs/erofs/zdata.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index 3977e42b9516861bf3d59c072b6b8aaa6898dd8a..fe8121df9ef2f2404fc6e3f0fbbd6367f9ec2c67 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -1445,6 +1445,7 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
>   				       int bios)
>   {
>   	struct erofs_sb_info *const sbi = EROFS_SB(io->sb);
> +	int gfp_flag;
>   
>   	/* wake up the caller thread for sync decompression */
>   	if (io->sync) {
> @@ -1477,7 +1478,9 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
>   			sbi->sync_decompress = EROFS_SYNC_DECOMPRESS_FORCE_ON;
>   		return;
>   	}
> +	gfp_flag = memalloc_noio_save();
>   	z_erofs_decompressqueue_work(&io->u.work);
> +	memalloc_noio_restore(gfp_flag);
>   }
>   
>   static void z_erofs_fill_bio_vec(struct bio_vec *bvec,
>
> ---
> base-commit: 11439c4635edd669ae435eec308f4ab8a0804808
> change-id: 20260311-origin-dev-1c9665798204
>
> Best regards,