linux-kernel - Re: [PATCH] mm: shmem: avoid build warning for CONFIG

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Message-ID: <861plamuoc.fsf@kernel.org>
Date: Thu, 04 Dec 2025 11:02:27 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Hugh Dickins <hughd@...gle.com>,  Andrew Morton
 <akpm@...ux-foundation.org>,  "Mike Rapoport (Microsoft)"
 <rppt@...nel.org>,  Pasha Tatashin <pasha.tatashin@...een.com>,  Pratyush
 Yadav <pratyush@...nel.org>,  Arnd Bergmann <arnd@...db.de>,  Baolin Wang
 <baolin.wang@...ux.alibaba.com>,  Kairui Song <kasong@...cent.com>,  David
 Hildenbrand <david@...nel.org>,  Christian Brauner <brauner@...nel.org>,
  Kemeng Shi <shikemeng@...weicloud.com>,  Lorenzo Stoakes
 <lorenzo.stoakes@...cle.com>,  Guo Weikang <guoweikang.kernel@...il.com>,
  linux-mm@...ck.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: shmem: avoid build warning for CONFIG_SHMEM=n

Hi Arnd,

On Thu, Dec 04 2025, Arnd Bergmann wrote:

> From: Arnd Bergmann <arnd@...db.de>
>
> The newly added 'flags' variable is unused and causes a warning if
> CONFIG_SHMEM is disabled, since the shmem_acct_size() macro it is passed
> into does nothing:
>
> mm/shmem.c: In function '__shmem_file_setup':
> mm/shmem.c:5816:23: error: unused variable 'flags' [-Werror=unused-variable]
>  5816 |         unsigned long flags = (vm_flags & VM_NORESERVE) ? SHMEM_F_NORESERVE : 0;
>       |                       ^~~~~
>
> Replace the macro with an equivalent inline function to get the
> argument checking.
>
> Fixes: 6ff1610ced56 ("mm: shmem: use SHMEM_F_* flags instead of VM_* flags")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for the fix!

I recall that the kernel test robot also reported something similar, and
Andrew sent out a fix for that [0]. But I guess it got dropped in the
later re-rolls of the patchset.

> ---
>  mm/shmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 3f194c9842a8..93746270c459 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -5794,7 +5794,7 @@ EXPORT_SYMBOL_GPL(shmem_truncate_range);
>  #define shmem_vm_ops				generic_file_vm_ops
>  #define shmem_anon_vm_ops			generic_file_vm_ops
>  #define shmem_file_operations			ramfs_file_operations
> -#define shmem_acct_size(flags, size)		0
> +static inline int shmem_acct_size(unsigned long flags, loff_t size) { return 0; }
>  #define shmem_unacct_size(flags, size)		do {} while (0)

Can you please also make shmem_unacct_size() an inline function for
consistency?

>  
>  static inline struct inode *shmem_get_inode(struct mnt_idmap *idmap,

[0] https://lore.kernel.org/all/20251108084308.8640699dc4f737c520841391@linux-foundation.org/

-- 
Regards,
Pratyush Yadav