Re: [PATCH 9/9] filemap: Remove FGP_NOFS

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Undeclared identifier 'FGP_NOFS' causes compilation failure in f2fs, and trivial removal introduces a filesystem reclaim deadlock.
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commit 1683abf08ae4fef5fa05b44d804e2e0ac6771ec5
Author: Matthew Wilcox (Oracle) <willy@infradead.org>

filemap: Remove FGP_NOFS

This commit removes the FGP_NOFS flag and its associated __GFP_FS clearing
logic, stating that there are no more users of it.

> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 3974b063a0496..bff8b7264fb02 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
[ ... ]
> @@ -710,11 +709,10 @@ typedef unsigned int __bitwise fgf_t;
>  #define FGP_LOCK		((__force fgf_t)0x00000002)
>  #define FGP_CREAT		((__force fgf_t)0x00000004)
>  #define FGP_WRITE		((__force fgf_t)0x00000008)
> -#define FGP_NOFS		((__force fgf_t)0x00000010)

[Severity: Low]
Does this removal break the build for f2fs?

Looking at f2fs_write_begin() in fs/f2fs/data.c, it still relies on the
removed FGP_NOFS flag:

	folio = f2fs_filemap_get_folio(mapping, index,
				FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_NOFS,
				mapping_gfp_mask(mapping));

> diff --git a/mm/filemap.c b/mm/filemap.c
> index 6afec636881fb..e6580291f2185 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1994,8 +1994,6 @@ struct folio *__filemap_get_folio_mpol(struct address_space *mapping,
>  
>  		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
>  			gfp |= __GFP_WRITE;
> -		if (fgp_flags & FGP_NOFS)
> -			gfp &= ~__GFP_FS;

[Severity: Low]
If the build failure is trivially fixed by simply deleting FGP_NOFS from
f2fs_write_begin() without adding a memalloc_nofs_save() wrapper, will this
introduce an ABBA deadlock during direct reclaim?

Because __filemap_get_folio_mpol() no longer clears __GFP_FS, this could
allow __GFP_FS to bleed into the allocator while f2fs calls this holding
internal filesystem locks.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260830041901.2668-1-willy@infradead.org?part=9