linux-kernel - Re: [PATCH] fs: drop assert in file_seek_cur_needs_f

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Message-ID: <tsevuodksvhftqyobfu6ana5ibbbdtbqo46j5r3hir5kvmpozo@g3vcsirgdioe>
Date: Thu, 12 Jun 2025 13:08:19 +0200
From: Jan Kara <jack@...e.cz>
To: Luis Henriques <luis@...lia.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kernel-dev@...lia.com
Subject: Re: [PATCH] fs: drop assert in file_seek_cur_needs_f_lock

On Thu 12-06-25 10:41:01, Luis Henriques wrote:
> The assert in function file_seek_cur_needs_f_lock() can be triggered very
> easily because, as Jan Kara suggested, the file reference may get
> incremented after checking it with fdget_pos().
> 
> Fixes: da06e3c51794 ("fs: don't needlessly acquire f_lock")
> Signed-off-by: Luis Henriques <luis@...lia.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
> ---
> Hi Christian,
> 
> It wasn't clear whether you'd be queueing this fix yourself.  Since I don't
> see it on vfs.git, I decided to explicitly send the patch so that it doesn't
> slip through the cracks.
> 
> Cheers,
> -- 
> Luis
> 
>  fs/file.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/fs/file.c b/fs/file.c
> index 3a3146664cf3..075f07bdc977 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -1198,8 +1198,6 @@ bool file_seek_cur_needs_f_lock(struct file *file)
>  	if (!(file->f_mode & FMODE_ATOMIC_POS) && !file->f_op->iterate_shared)
>  		return false;
>  
> -	VFS_WARN_ON_ONCE((file_count(file) > 1) &&
> -			 !mutex_is_locked(&file->f_pos_lock));
>  	return true;
>  }
>  
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR