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Date: Mon, 18 Jan 2021 21:56:29 +0100
From: Alexey Gladkov <>
To: Linus Torvalds <>
Cc: LKML <>,
	io-uring <>,
	Kernel Hardening <>,
	Linux Containers <>,
	Linux-MM <>,
	Andrew Morton <>,
	Christian Brauner <>,
	"Eric W . Biederman" <>,
	Jann Horn <>, Jens Axboe <>,
	Kees Cook <>, Oleg Nesterov <>
Subject: Re: [RFC PATCH v3 1/8] Use refcount_t for ucounts reference counting

On Mon, Jan 18, 2021 at 12:34:29PM -0800, Linus Torvalds wrote:
> On Mon, Jan 18, 2021 at 11:46 AM Alexey Gladkov
> <> wrote:
> >
> > Sorry about that. I thought that this code is not needed when switching
> > from int to refcount_t. I was wrong.
> Well, you _may_ be right. I personally didn't check how the return
> value is used.
> I only reacted to "it certainly _may_ be used, and there is absolutely
> no comment anywhere about why it wouldn't matter".

I have not found examples where checked the overflow after calling

For example in kernel/fork.c:2298 :


$ semind search signal_struct.sigcnt
def include/linux/sched/signal.h:83  		refcount_t		sigcnt;
m-- kernel/fork.c:723 put_signal_struct 		if (refcount_dec_and_test(&sig->sigcnt))
m-- kernel/fork.c:1571 copy_signal 		refcount_set(&sig->sigcnt, 1);
m-- kernel/fork.c:2298 copy_process 				refcount_inc(&current->signal->sigcnt);

It seems to me that the only way is to use __refcount_inc and then compare
the old value with REFCOUNT_MAX

Since I have not seen examples of such checks, I thought that this is
acceptable. Sorry once again. I have not tried to hide these changes.

Rgrds, legion

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