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Date: Wed, 7 Aug 2024 09:29:36 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: "Tze-nan Wu (=?UTF-8?B?5ZCz5r6k5Y2X?=)" <Tze-nan.Wu@mediatek.com>
Cc: "zanussi@kernel.org" <zanussi@kernel.org>,
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 "mathieu.desnoyers@efficios.com" <mathieu.desnoyers@efficios.com>
Subject: Re: [PATCH RESEND] tracing: Fix overflow in get_free_elt()
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On Wed, 7 Aug 2024 11:34:43 +0000
Tze-nan Wu (=E5=90=B3=E6=BE=A4=E5=8D=97) <Tze-nan.Wu@mediatek.com> wrote:

> > > -idx =3D atomic_inc_return(&map->next_elt);
> > > +idx =3D atomic_fetch_add_unless(&map->next_elt, 1, map->max_elts); =
=20
> >=20
> > I guess we need to add (with a comment):
> >=20
> > idx--;
> >  =20
> Thanks for reviewing this!
>=20
> By reference to "/include/linux/atomic/atomic-instrumented.h",
> `atomic_fetch_add_unless` will return the original value before the
> adding happens on operands.

Ah, right. I haven't used that before and was thinking this was the same as
the inc_return().

-- Steve