Re: [PATCH 2/2] mtd: ubi: use GFP_NOIO for lock tree entry allocation

[Zhihao Cheng <chengzhihao1@huawei.com>]

在 2026/10/15 15:33, Yelin Fei 写道:
> From: Ye Linfei <yelinfei@ruijie.com.cn>
> 
> The per-LEB lock tree entry can be allocated while UBI is executing on
> behalf of a synchronous block-layer consumer (ubiblock), where issuing
> further block I/O from direct reclaim would deadlock; see the
> preceding commit "mtd: ubi: block: forbid direct reclaim I/O during
> synchronous read" for the full analysis.
> 
> Make the allocation self-contained: GFP_NOIO restricts direct reclaim
> to dropping clean page cache and shrinking slabs, page (swap) reclaim
> is left to kswapd, and the worst case is -ENOMEM, which callers
> already propagate as an ordinary recoverable I/O error.
> 
> memalloc_noio_save()/memalloc_noio_restore() in ubiblock_read()
> already enforce this for the whole read scope; keeping the allocation
> here self-contained as well means the safety property does not depend
> on every future caller remembering to set up that scope.

The ltree_add_entry() has many callers that not need GFP_NOIO, I think 
'mtd: ubi: block: forbid direct reclaim I/O during
 > synchronous read' is enough.
> 
> Signed-off-by: Ye Linfei <yelinfei@ruijie.com.cn>
> ---
>   drivers/mtd/ubi/eba.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
> index f0c549e62c55..8fe68e7fff58 100644
> --- a/drivers/mtd/ubi/eba.c
> +++ b/drivers/mtd/ubi/eba.c
> @@ -247,7 +247,7 @@ static struct ubi_ltree_entry *ltree_add_entry(struct ubi_device *ubi,
>   {
>   	struct ubi_ltree_entry *le, *le1, *le_free;
>   
> -	le = kmalloc_obj(struct ubi_ltree_entry, GFP_NOFS);
> +	le = kmalloc_obj(struct ubi_ltree_entry, GFP_NOIO); /* see ubiblock_read() */
>   	if (!le)
>   		return ERR_PTR(-ENOMEM);
>   
> 


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