linux-kernel - Re: [PATCH] debugfs: Fix __rcu type comparison warning

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Message-ID: <d11a47c9-c422-47d8-9049-2743314a9924@kernel.org>
Date:   Tue, 10 Oct 2023 00:45:32 +0300
From:   Georgi Djakov <djakov@...nel.org>
To:     Mike Tipton <quic_mdtipton@...cinc.com>, gregkh@...uxfoundation.org
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] debugfs: Fix __rcu type comparison warning

On 22.09.23 16:45, Mike Tipton wrote:
> Sparse reports the following:
> 
> fs/debugfs/file.c:942:9: sparse: sparse: incompatible types in comparison expression (different address spaces):
> fs/debugfs/file.c:942:9: sparse:    char [noderef] __rcu *
> fs/debugfs/file.c:942:9: sparse:    char *
> 
> rcu_assign_pointer() expects that it's assigning to pointers annotated
> with __rcu. We can't annotate the generic struct file::private_data, so
> cast it instead.
> 
> Fixes: 86b5488121db ("debugfs: Add write support to debugfs_create_str()")
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202309091933.BRWlSnCq-lkp@intel.com/
> Signed-off-by: Mike Tipton <quic_mdtipton@...cinc.com>

Reviewed-by: Georgi Djakov <djakov@...nel.org>

> ---
>   fs/debugfs/file.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> index 87b3753aa4b1..c45e8c2d62e1 100644
> --- a/fs/debugfs/file.c
> +++ b/fs/debugfs/file.c
> @@ -939,7 +939,7 @@ static ssize_t debugfs_write_file_str(struct file *file, const char __user *user
>   	new[pos + count] = '\0';
>   	strim(new);
>   
> -	rcu_assign_pointer(*(char **)file->private_data, new);
> +	rcu_assign_pointer(*(char __rcu **)file->private_data, new);
>   	synchronize_rcu();
>   	kfree(old);
>