Re: fs/locks.c: Fix sys_flock() race

[Andrew Morton]

Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> wrote:
>
> -	unlock_kernel();
>  
> -	if (new_fl->fl_type == F_UNLCK)
> -		return 0;
> +	if (request->fl_type == F_UNLCK)
> +		goto out;
>  
> +	new_fl = locks_alloc_lock();
> +	if (new_fl == NULL)
> +		goto out;
>  	/*
>  	 * If a higher-priority process was blocked on the old file lock,
>  	 * give it the opportunity to lock the file.
> @@ -769,26 +772,27 @@ static int flock_lock_file(struct file *
>  	if (found)
>  		cond_resched();
>  
> -	lock_kernel();

hm, you've extended lock_kernel() coverage (why?  Does this help fix the
race??) but we still have a cond_resched() inside the now-newly-locked
region.  If that cond_resched() drops the bkl, is the race reopened?
-
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