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From: Oleg Nesterov <oleg@redhat.com>
To: Marco Elver <elver@google.com>
Cc: LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Alexander Potapenko <glider@google.com>,
	Andrea Parri <parri.andrea@gmail.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>, Boqun Feng <boqun.feng@gmail.com>,
	Borislav Petkov <bp@alien8.de>, Daniel Axtens <dja@axtens.net>,
	Daniel Lustig <dlustig@nvidia.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	David Howells <dhowells@redhat.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Joel Fernandes <joel@joelfernandes.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Luc Maranget <luc.maranget@inria.fr>,
	Mark Rutland <mark.rutland@arm.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	linux-efi@vger.kernel.org,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [PATCH v2 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure
Date: Wed, 23 Oct 2019 18:24:32 +0200	[thread overview]
Message-ID: <20191023162432.GC14327@redhat.com> (raw)
In-Reply-To: <CANpmjNPUT2B3rWaa=5Ee2Xs3HHDaUiBGpG09Q4h9Gemhsp9KFw@mail.gmail.com>

On 10/22, Marco Elver wrote:
>
> On Tue, 22 Oct 2019 at 17:49, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > Just for example. Suppose that task->state = TASK_UNINTERRUPTIBLE, this task
> > does __set_current_state(TASK_RUNNING), another CPU does wake_up_process(task)
> > which does the same UNINTERRUPTIBLE -> RUNNING transition.
> >
> > Looks like, this is the "data race" according to kcsan?
>
> Yes, they are "data races". They are probably not "race conditions" though.
>
> This is a fair distinction to make, and we never claimed to find "race
> conditions" only

I see, thanks, just wanted to be sure...

> KCSAN's goal is to find *data races* according to the LKMM.  Some data
> races are race conditions (usually the more interesting bugs) -- but
> not *all* data races are race conditions. Those are what are usually
> referred to as "benign", but they can still become bugs on the wrong
> arch/compiler combination. Hence, the need to annotate these accesses
> with READ_ONCE, WRITE_ONCE or use atomic_t:

Well, if I see READ_ONCE() in the code I want to understand why it was
used. Is it really needed for correctness or we want to shut up kcsan?
Say, why should wait_event(wq, *ptr) use READ_ONCE()? Nevermind, please
forget.

Btw, why __kcsan_check_watchpoint() does user_access_save() before
try_consume_watchpoint() ?

Oleg.


WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: Marco Elver <elver@google.com>
Cc: LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Alexander Potapenko <glider@google.com>,
	Andrea Parri <parri.andrea@gmail.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>, Boqun Feng <boqun.feng@gmail.com>,
	Borislav Petkov <bp@alien8.de>, Daniel Axtens <dja@axtens.net>,
	Daniel Lustig <dlustig@nvidia.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	David Howells <dhowells@redhat.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Joel Fernandes <joel@joelfernandes.org>,
	Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH v2 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure
Date: Wed, 23 Oct 2019 18:24:32 +0200	[thread overview]
Message-ID: <20191023162432.GC14327@redhat.com> (raw)
In-Reply-To: <CANpmjNPUT2B3rWaa=5Ee2Xs3HHDaUiBGpG09Q4h9Gemhsp9KFw@mail.gmail.com>

On 10/22, Marco Elver wrote:
>
> On Tue, 22 Oct 2019 at 17:49, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > Just for example. Suppose that task->state = TASK_UNINTERRUPTIBLE, this task
> > does __set_current_state(TASK_RUNNING), another CPU does wake_up_process(task)
> > which does the same UNINTERRUPTIBLE -> RUNNING transition.
> >
> > Looks like, this is the "data race" according to kcsan?
>
> Yes, they are "data races". They are probably not "race conditions" though.
>
> This is a fair distinction to make, and we never claimed to find "race
> conditions" only

I see, thanks, just wanted to be sure...

> KCSAN's goal is to find *data races* according to the LKMM.  Some data
> races are race conditions (usually the more interesting bugs) -- but
> not *all* data races are race conditions. Those are what are usually
> referred to as "benign", but they can still become bugs on the wrong
> arch/compiler combination. Hence, the need to annotate these accesses
> with READ_ONCE, WRITE_ONCE or use atomic_t:

Well, if I see READ_ONCE() in the code I want to understand why it was
used. Is it really needed for correctness or we want to shut up kcsan?
Say, why should wait_event(wq, *ptr) use READ_ONCE()? Nevermind, please
forget.

Btw, why __kcsan_check_watchpoint() does user_access_save() before
try_consume_watchpoint() ?

Oleg.

  reply	other threads:[~2019-10-23 16:24 UTC|newest]

Thread overview: 88+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-17 14:12 [PATCH v2 0/8] Add Kernel Concurrency Sanitizer (KCSAN) Marco Elver
2019-10-17 14:12 ` Marco Elver
2019-10-17 14:12 ` [PATCH v2 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure Marco Elver
2019-10-17 14:12   ` Marco Elver
2019-10-21 13:37   ` Alexander Potapenko
2019-10-21 13:37     ` Alexander Potapenko
2019-10-21 13:37     ` Alexander Potapenko
2019-10-21 15:54     ` Marco Elver
2019-10-21 15:54       ` Marco Elver
2019-10-21 15:54       ` Marco Elver
2019-10-21 15:54       ` Marco Elver
2019-10-22 14:11   ` Mark Rutland
2019-10-22 16:52     ` Marco Elver
2019-10-22 16:52       ` Marco Elver
2019-10-22 16:52       ` Marco Elver
2019-10-22 15:48   ` Oleg Nesterov
2019-10-22 17:42     ` Marco Elver
2019-10-22 17:42       ` Marco Elver
2019-10-22 17:42       ` Marco Elver
2019-10-23 16:24       ` Oleg Nesterov [this message]
2019-10-23 16:24         ` Oleg Nesterov
2019-10-24 11:02         ` Marco Elver
2019-10-24 11:02           ` Marco Elver
2019-10-24 11:02           ` Marco Elver
2019-10-23  9:41   ` Dmitry Vyukov
2019-10-23  9:41     ` Dmitry Vyukov
2019-10-23  9:41     ` Dmitry Vyukov
2019-10-23  9:56   ` Dmitry Vyukov
2019-10-23  9:56     ` Dmitry Vyukov
2019-10-23  9:56     ` Dmitry Vyukov
2019-10-23 10:03   ` Dmitry Vyukov
2019-10-23 10:03     ` Dmitry Vyukov
2019-10-23 10:03     ` Dmitry Vyukov
2019-10-23 10:09   ` Dmitry Vyukov
2019-10-23 10:09     ` Dmitry Vyukov
2019-10-23 10:09     ` Dmitry Vyukov
2019-10-23 10:28   ` Dmitry Vyukov
2019-10-23 10:28     ` Dmitry Vyukov
2019-10-23 10:28     ` Dmitry Vyukov
2019-10-23 11:08   ` Dmitry Vyukov
2019-10-23 11:08     ` Dmitry Vyukov
2019-10-23 11:08     ` Dmitry Vyukov
2019-10-23 11:20   ` Dmitry Vyukov
2019-10-23 11:20     ` Dmitry Vyukov
2019-10-23 11:20     ` Dmitry Vyukov
2019-10-23 12:05   ` Dmitry Vyukov
2019-10-23 12:05     ` Dmitry Vyukov
2019-10-23 12:05     ` Dmitry Vyukov
2019-10-23 12:32   ` Dmitry Vyukov
2019-10-23 12:32     ` Dmitry Vyukov
2019-10-23 12:32     ` Dmitry Vyukov
2019-10-17 14:12 ` [PATCH v2 2/8] objtool, kcsan: Add KCSAN runtime functions to whitelist Marco Elver
2019-10-17 14:12   ` Marco Elver
2019-10-21 15:15   ` Dmitry Vyukov
2019-10-21 15:15     ` Dmitry Vyukov
2019-10-21 15:15     ` Dmitry Vyukov
2019-10-21 15:43     ` Marco Elver
2019-10-21 15:43       ` Marco Elver
2019-10-21 15:43       ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 3/8] build, kcsan: Add KCSAN build exceptions Marco Elver
2019-10-17 14:13   ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 4/8] seqlock, kcsan: Add annotations for KCSAN Marco Elver
2019-10-17 14:13   ` Marco Elver
2019-10-24 12:28   ` Mark Rutland
2019-10-24 14:17     ` Marco Elver
2019-10-24 14:17       ` Marco Elver
2019-10-24 14:17       ` Marco Elver
2019-10-24 16:35       ` Mark Rutland
2019-10-24 16:35         ` Mark Rutland
2019-10-24 17:09         ` Marco Elver
2019-10-24 17:09           ` Marco Elver
2019-10-24 17:09           ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 5/8] seqlock: Require WRITE_ONCE surrounding raw_seqcount_barrier Marco Elver
2019-10-17 14:13   ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 6/8] asm-generic, kcsan: Add KCSAN instrumentation for bitops Marco Elver
2019-10-17 14:13   ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 7/8] locking/atomics, kcsan: Add KCSAN instrumentation Marco Elver
2019-10-17 14:13   ` Marco Elver
2019-10-22 12:33   ` Mark Rutland
2019-10-22 18:17     ` Marco Elver
2019-10-22 18:17       ` Marco Elver
2019-10-22 18:17       ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 8/8] x86, kcsan: Enable KCSAN for x86 Marco Elver
2019-10-17 14:13   ` Marco Elver
2019-10-22 12:59   ` Mark Rutland
2019-10-22 13:02     ` Marco Elver
2019-10-22 13:02       ` Marco Elver
2019-10-22 13:02       ` Marco Elver

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