From: Peter Zijlstra <peterz@infradead•org>
To: Dmitry Vyukov <dvyukov@google•com>
Cc: "Paul E. McKenney" <paulmck@linux•ibm.com>,
Trond Myklebust <trondmy@hammerspace•com>,
"mark.rutland@arm•com" <mark.rutland@arm•com>,
"linux-kernel@vger•kernel.org" <linux-kernel@vger•kernel.org>,
"ralf@linux-mips•org" <ralf@linux-mips•org>,
"jlayton@kernel•org" <jlayton@kernel•org>,
"linuxppc-dev@lists•ozlabs.org" <linuxppc-dev@lists•ozlabs.org>,
"bfields@fieldses•org" <bfields@fieldses•org>,
"linux-mips@linux-mips•org" <linux-mips@linux-mips•org>,
"linux@roeck-us•net" <linux@roeck-us•net>,
"linux-nfs@vger•kernel.org" <linux-nfs@vger•kernel.org>,
"akpm@linux-foundation•org" <akpm@linux-foundation•org>,
"will.deacon@arm•com" <will.deacon@arm•com>,
"boqun.feng@gmail•com" <boqun.feng@gmail•com>,
"paul.burton@mips•com" <paul.burton@mips•com>,
"anna.schumaker@netapp•com
Subject: Re: [RFC PATCH] lib: Introduce generic __cmpxchg_u64() and use it where needed
Date: Thu, 1 Nov 2018 22:45:29 +0100 [thread overview]
Message-ID: <20181101214529.GB3339@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <CACT4Y+aC45BtS88DXarn3A+LV2RRRsPQoSs_3_DnKjU4O3AMHQ@mail.gmail.com>
On Thu, Nov 01, 2018 at 06:46:50PM +0100, Dmitry Vyukov wrote:
> If there is a warning that we don't want to see at all, then we can
> disable it. It supposed to be a useful tool, rather than a thing in
> itself that lives own life. We already I think removed 1 particularly
> noisy warning and made another optional via a config.
> But the thing with overflows is that, even if it's defined, it's not
> necessary the intended behavior. For example, take allocation size
> calculation done via unsigned size_t. If it overflows it does not help
> if C defines result or not, it still gives a user controlled write
> primitive. We've seen similar cases with timeout/deadline calculation
> in kernel, we really don't want it to just wrap modulo-2, right. Some
> user-space projects even test with unsigned overflow warnings or
> implicit truncation warnings, which are formally legal, but frequently
> bugs.
Sure; but then don't call it UB.
If we want to have an additional integer over/underflow checker (ideally
with a gcc plugin that has explicit annotations like __wrap to make it
go away) that is fine; and it can be done on unsigned and signed.
next prev parent reply other threads:[~2018-11-01 21:45 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1541015538-11382-1-git-send-email-linux@roeck-us.net>
[not found] ` <20181031213240.zhh7dfcm47ucuyfl@pburton-laptop>
[not found] ` <20181031220253.GA15505@roeck-us.net>
2018-10-31 23:32 ` [RFC PATCH] lib: Introduce generic __cmpxchg_u64() and use it where needed Paul Burton
2018-11-01 0:17 ` Trond Myklebust
2018-11-01 13:18 ` Mark Rutland
2018-11-01 14:59 ` Peter Zijlstra
2018-11-01 15:22 ` Trond Myklebust
2018-11-01 16:32 ` Peter Zijlstra
2018-11-01 16:59 ` Eric Dumazet
2018-11-01 17:14 ` Peter Zijlstra
2018-11-01 17:27 ` Peter Zijlstra
2018-11-01 20:29 ` Paul E. McKenney
2018-11-01 21:38 ` Peter Zijlstra
2018-11-01 22:26 ` Paul E. McKenney
2018-11-01 17:43 ` Paul E. McKenney
2018-11-01 17:01 ` Paul E. McKenney
2018-11-01 17:18 ` Peter Zijlstra
2018-11-01 17:34 ` Paul E. McKenney
2018-11-01 17:46 ` Dmitry Vyukov
2018-11-01 21:45 ` Peter Zijlstra [this message]
2018-11-02 10:56 ` David Laight
2018-11-02 12:23 ` Peter Zijlstra
2018-11-02 13:38 ` Paul E. McKenney
2018-11-02 13:37 ` Paul E. McKenney
2018-11-02 16:19 ` Andrey Ryabinin
2018-11-05 10:38 ` Peter Zijlstra
2018-11-05 14:24 ` Peter Zijlstra
2018-11-01 17:51 ` [PATCH] SUNRPC: Use atomic(64)_t for seq_send(64) Paul Burton
2018-11-01 17:57 ` Trond Myklebust
2018-11-01 17:54 ` [RFC PATCH] lib: Introduce generic __cmpxchg_u64() and use it where needed Paul Burton
2018-11-01 1:18 ` Guenter Roeck
2018-11-01 6:30 ` Trond Myklebust
2018-11-01 15:28 ` Guenter Roeck
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