From: Thomas Gleixner <tglx@linutronix.de>
To: Christophe Leroy <christophe.leroy@c-s.fr>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
arnd@arndb.de, vincenzo.frascino@arm.com, luto@kernel.org
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
x86@kernel.org
Subject: Re: [RFC PATCH v2 07/10] lib: vdso: don't use READ_ONCE() in __c_kernel_time()
Date: Fri, 10 Jan 2020 22:12:06 +0100 [thread overview]
Message-ID: <87lfqfrp7d.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <fc1ff722c7cbe63a63ae02ade3a714d2049d54a5.1577111367.git.christophe.leroy@c-s.fr>
Christophe Leroy <christophe.leroy@c-s.fr> writes:
>
> diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
> index 17b4cff6e5f0..5a17a9d2e6cd 100644
> --- a/lib/vdso/gettimeofday.c
> +++ b/lib/vdso/gettimeofday.c
> @@ -144,7 +144,7 @@ __cvdso_gettimeofday(const struct vdso_data *vd, struct __kernel_old_timeval *tv
> static __maybe_unused __kernel_old_time_t
> __cvdso_time(const struct vdso_data *vd, __kernel_old_time_t *time)
> {
> - __kernel_old_time_t t = READ_ONCE(vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec);
> + __kernel_old_time_t t = vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec;
>
> if (time)
> *time = t;
Allows the compiler to load twice, i.e. the returned value might be different from the
stored value. So no.
Thanks,
tglx
WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: Christophe Leroy <christophe.leroy@c-s.fr>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
arnd@arndb.de, vincenzo.frascino@arm.com, luto@kernel.org
Cc: x86@kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org
Subject: Re: [RFC PATCH v2 07/10] lib: vdso: don't use READ_ONCE() in __c_kernel_time()
Date: Fri, 10 Jan 2020 22:12:06 +0100 [thread overview]
Message-ID: <87lfqfrp7d.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <fc1ff722c7cbe63a63ae02ade3a714d2049d54a5.1577111367.git.christophe.leroy@c-s.fr>
Christophe Leroy <christophe.leroy@c-s.fr> writes:
>
> diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
> index 17b4cff6e5f0..5a17a9d2e6cd 100644
> --- a/lib/vdso/gettimeofday.c
> +++ b/lib/vdso/gettimeofday.c
> @@ -144,7 +144,7 @@ __cvdso_gettimeofday(const struct vdso_data *vd, struct __kernel_old_timeval *tv
> static __maybe_unused __kernel_old_time_t
> __cvdso_time(const struct vdso_data *vd, __kernel_old_time_t *time)
> {
> - __kernel_old_time_t t = READ_ONCE(vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec);
> + __kernel_old_time_t t = vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec;
>
> if (time)
> *time = t;
Allows the compiler to load twice, i.e. the returned value might be different from the
stored value. So no.
Thanks,
tglx
WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: Christophe Leroy <christophe.leroy@c-s.fr>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
arnd@arndb.de, vincenzo.frascino@arm.com, luto@kernel.org
Cc: x86@kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org
Subject: Re: [RFC PATCH v2 07/10] lib: vdso: don't use READ_ONCE() in __c_kernel_time()
Date: Fri, 10 Jan 2020 22:12:06 +0100 [thread overview]
Message-ID: <87lfqfrp7d.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <fc1ff722c7cbe63a63ae02ade3a714d2049d54a5.1577111367.git.christophe.leroy@c-s.fr>
Christophe Leroy <christophe.leroy@c-s.fr> writes:
>
> diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
> index 17b4cff6e5f0..5a17a9d2e6cd 100644
> --- a/lib/vdso/gettimeofday.c
> +++ b/lib/vdso/gettimeofday.c
> @@ -144,7 +144,7 @@ __cvdso_gettimeofday(const struct vdso_data *vd, struct __kernel_old_timeval *tv
> static __maybe_unused __kernel_old_time_t
> __cvdso_time(const struct vdso_data *vd, __kernel_old_time_t *time)
> {
> - __kernel_old_time_t t = READ_ONCE(vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec);
> + __kernel_old_time_t t = vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec;
>
> if (time)
> *time = t;
Allows the compiler to load twice, i.e. the returned value might be different from the
stored value. So no.
Thanks,
tglx
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next prev parent reply other threads:[~2020-01-10 21:12 UTC|newest]
Thread overview: 137+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-23 14:31 [RFC PATCH v2 00/10] powerpc/32: switch VDSO to C implementation Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 01/10] lib: vdso: ensure all arches have 32bit fallback Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-24 2:07 ` Andy Lutomirski
2019-12-24 2:07 ` Andy Lutomirski
2019-12-24 2:07 ` Andy Lutomirski
2020-01-10 20:56 ` Thomas Gleixner
2020-01-10 20:56 ` Thomas Gleixner
2020-01-10 20:56 ` Thomas Gleixner
2020-01-10 21:02 ` Andy Lutomirski
2020-01-10 21:02 ` Andy Lutomirski
2020-01-10 21:02 ` Andy Lutomirski
2019-12-25 2:05 ` kbuild test robot
2019-12-25 6:01 ` kbuild test robot
2019-12-30 12:27 ` Arnd Bergmann
2019-12-30 12:27 ` Arnd Bergmann
2019-12-30 12:27 ` Arnd Bergmann
2020-01-02 11:29 ` Arnd Bergmann
2020-01-02 11:29 ` Arnd Bergmann
2020-01-02 11:29 ` Arnd Bergmann
2020-01-09 15:43 ` Christophe Leroy
2020-01-09 15:43 ` Christophe Leroy
2020-01-09 15:43 ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 02/10] lib: vdso: move call to fallback out of common code Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-24 2:24 ` Andy Lutomirski
2019-12-24 2:24 ` Andy Lutomirski
2019-12-24 2:24 ` Andy Lutomirski
2019-12-24 11:41 ` christophe leroy
2019-12-24 11:41 ` christophe leroy
2019-12-24 11:41 ` christophe leroy
2019-12-24 12:09 ` Andy Lutomirski
2019-12-24 12:09 ` Andy Lutomirski
2019-12-24 12:09 ` Andy Lutomirski
2019-12-25 2:19 ` kbuild test robot
2019-12-23 14:31 ` [RFC PATCH v2 03/10] lib: vdso: Change __cvdso_clock_gettime/getres_common() to __cvdso_clock_gettime/getres() Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 04/10] lib: vdso: get pointer to vdso data from the arch Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-24 2:27 ` Andy Lutomirski
2019-12-24 2:27 ` Andy Lutomirski
2019-12-24 2:27 ` Andy Lutomirski
2019-12-24 11:53 ` christophe leroy
2019-12-24 11:53 ` christophe leroy
2019-12-24 11:53 ` christophe leroy
2019-12-24 12:15 ` Andy Lutomirski
2019-12-24 12:15 ` Andy Lutomirski
2019-12-24 12:15 ` Andy Lutomirski
2019-12-24 12:41 ` Andy Lutomirski
2019-12-24 12:41 ` Andy Lutomirski
2019-12-24 12:41 ` Andy Lutomirski
2019-12-24 14:46 ` Segher Boessenkool
2019-12-24 14:46 ` Segher Boessenkool
2019-12-24 14:46 ` Segher Boessenkool
2019-12-23 14:31 ` [RFC PATCH v2 05/10] lib: vdso: inline do_hres() Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-24 2:29 ` Andy Lutomirski
2019-12-24 2:29 ` Andy Lutomirski
2019-12-24 2:29 ` Andy Lutomirski
2019-12-30 12:07 ` Arnd Bergmann
2019-12-30 12:07 ` Arnd Bergmann
2019-12-30 12:07 ` Arnd Bergmann
2020-01-10 21:07 ` Thomas Gleixner
2020-01-10 21:07 ` Thomas Gleixner
2020-01-10 21:07 ` Thomas Gleixner
2020-01-11 9:06 ` Christophe Leroy
2020-01-11 9:06 ` Christophe Leroy
2020-01-11 9:06 ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 06/10] lib: vdso: make do_coarse() return 0 Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 07/10] lib: vdso: don't use READ_ONCE() in __c_kernel_time() Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-24 1:58 ` Andy Lutomirski
2019-12-24 1:58 ` Andy Lutomirski
2019-12-24 1:58 ` Andy Lutomirski
2019-12-24 11:12 ` christophe leroy
2019-12-24 11:12 ` christophe leroy
2019-12-24 11:12 ` christophe leroy
2019-12-24 12:04 ` Andy Lutomirski
2019-12-24 12:04 ` Andy Lutomirski
2019-12-24 12:04 ` Andy Lutomirski
2020-01-10 21:12 ` Thomas Gleixner [this message]
2020-01-10 21:12 ` Thomas Gleixner
2020-01-10 21:12 ` Thomas Gleixner
2020-01-11 8:05 ` Christophe Leroy
2020-01-11 8:05 ` Christophe Leroy
2020-01-11 8:05 ` Christophe Leroy
2020-01-11 11:07 ` Thomas Gleixner
2020-01-11 11:07 ` Thomas Gleixner
2020-01-11 11:07 ` Thomas Gleixner
2020-01-13 6:52 ` Christophe Leroy
2020-01-13 6:52 ` Christophe Leroy
2020-01-13 6:52 ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 08/10] lib: vdso: Avoid duplication in __cvdso_clock_getres() Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-24 1:59 ` Andy Lutomirski
2019-12-24 1:59 ` Andy Lutomirski
2019-12-24 1:59 ` Andy Lutomirski
2019-12-23 14:31 ` [RFC PATCH v2 09/10] powerpc/vdso32: inline __get_datapage() Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 10/10] powerpc/32: Switch VDSO to C implementation Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-23 14:31 ` Christophe Leroy
2019-12-25 6:54 ` kbuild test robot
2020-01-09 17:52 ` Surprising code generated for vdso_read_begin() Christophe Leroy
2020-01-09 20:07 ` Segher Boessenkool
2020-01-09 20:07 ` Segher Boessenkool
2020-01-09 20:07 ` Segher Boessenkool
2020-01-10 6:45 ` Christophe Leroy
2020-01-10 6:45 ` Christophe Leroy
2020-01-10 6:45 ` Christophe Leroy
2020-01-11 11:33 ` Segher Boessenkool
2020-01-11 11:33 ` Segher Boessenkool
2020-01-11 11:33 ` Segher Boessenkool
2020-02-16 18:10 ` Arnd Bergmann
2020-02-16 18:10 ` Arnd Bergmann
2020-02-16 18:10 ` Arnd Bergmann
2020-02-19 8:45 ` Christophe Leroy
2020-02-19 8:45 ` Christophe Leroy
2020-02-19 8:45 ` Christophe Leroy
2020-02-19 9:52 ` Arnd Bergmann
2020-02-19 9:52 ` Arnd Bergmann
2020-02-19 9:52 ` Arnd Bergmann
2020-02-19 13:08 ` Segher Boessenkool
2020-02-19 13:08 ` Segher Boessenkool
2020-02-19 13:08 ` Segher Boessenkool
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