Re: [PATCH v2] erofs: add GFP_NOIO in the bio completion if needed

[Chao Yu]

On 2026/3/11 17:11, Jiucheng Xu via B4 Relay wrote:
> From: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>
>
> 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, vm_map_ram() 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.
>
> Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,