linux-kernel - Re: [PATCH 1/5] sched: convert sighand_struct.count to refcount

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Date:   Mon, 21 Jan 2019 18:05:12 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Elena Reshetova <elena.reshetova@...el.com>
Cc:     mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        keescook@...omium.org, tglx@...utronix.de
Subject: Re: [PATCH 1/5] sched: convert sighand_struct.count to refcount_t

On 01/18, Elena Reshetova wrote:
>
> --- a/fs/proc/task_nommu.c
> +++ b/fs/proc/task_nommu.c
> @@ -64,7 +64,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
>  	else
>  		bytes += kobjsize(current->files);
>  
> -	if (current->sighand && atomic_read(&current->sighand->count) > 1)
> +	if (current->sighand && refcount_read(&current->sighand->count) > 1)
>  		sbytes += kobjsize(current->sighand);
>  	else
>  		bytes += kobjsize(current->sighand);

I fail to understand this code with or without the patch... I do not see
how is it possible to hit ->sighand == NULL or sighand->count == 0 in
proc_pid_status() paths.

Nevermind, this is off-topic.

Reviewed-by: Oleg Nesterov <oleg@...hat.com>