From: ebiederm@xmission.com (Eric W. Biederman)
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Rich Felker <dalias@libc.org>,
Alistair Francis <alistair.francis@wdc.com>,
GNU C Library <libc-alpha@sourceware.org>,
Adhemerval Zanella <adhemerval.zanella@linaro.org>,
Florian Weimer <fweimer@redhat.com>,
Palmer Dabbelt <palmer@sifive.com>,
macro@wdc.com, Zong Li <zongbox@gmail.com>,
Alistair Francis <alistair23@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <christian@brauner.io>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [RFC v3 03/23] sysdeps/wait: Use waitid if avaliable
Date: Sun, 21 Jul 2019 21:40:00 -0000 [thread overview]
Message-ID: <87blxn83sk.fsf@xmission.com> (raw)
In-Reply-To: <CAHk-=wjtGaJFceL+YB6=mTxQCvyNvBTavqgGTm-d5FA9xLQ0Cw@mail.gmail.com> (Linus Torvalds's message of "Sun, 21 Jul 2019 10:16:19 -0700")
Linus Torvalds <torvalds@linux-foundation.org> writes:
> On Sun, Jul 21, 2019 at 8:45 AM Eric W. Biederman <ebiederm@xmission.com> wrote:
>>
>> We either add P_PROCESS_PGID to the kernel's waitid or we add wait4.
>
> Do we actually need a new flag?
>
> Why not just allow people to pass in pid = 0 with the existing P_PGID flag?
>
> Those are the traditional and documented waitpid() semantics. Why
> wouldn't we use those semantics for waitid() too?
>
> And since our current (broken) waitid() returns EINVAL for that case,
> it's even trivial to test for in user space (and fall back on the
> broken racy code in user space - which you have to do anyway).
Our current waitid implementation when serving as waitid is not broken.
What is broken is the waitpid emulation on top of waitid.
The way waitid is defined waitid P_PGID with a pid of 0 means
wait for the process group id of 0. Which in theory and in limited
practice exists. AKA that is the pid and process group of the idle
thread.
Further there is the outstanding question. Should P_PROCESS_PGID refer
to the curent processes process group id at the time of the waitid call,
or should P_PROCESS_PGID refer to the process group id when a child is
found?
It has been suggested elswehere in this conversation that 161550d74c07
("pid: sys_wait... fixes") may have introduced a regression. If so
the current wait4 behavior of capturing the process group at the time
of call is wrong and needs to be fixed.
Not capuring the pid at time time of call is a very different behavior
of P_PROCESS_PGID vs all of the other waitid cases which do have the pid
fixed at the time of the call which further argues a separate flag
because the behavior would be distinctly different.
> Honestly, that seems like the simplest soilution, but also like the
> only sane model. The fact that P_PGID with a zero pid doesn't work
> seems to simply be a bug right now, and keeps waitid() from being a
> proper superset of waitpid().
In the context of waitid it does not look sane. Unlike the other wait
functions waitid does not have any magic ids and by having an idtype
field makes that kind of magic unnecessary. Further it is trivial
to add one line to the architecture independent enumeration and have 0
risk of confusion or of regressing user space.
Eric
next prev parent reply other threads:[~2019-07-21 21:40 UTC|newest]
Thread overview: 127+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-17 0:11 [RFC v3 00/23] RISC-V glibc port for the 32-bit Alistair Francis
2019-07-17 0:11 ` [RFC v3 03/23] sysdeps/wait: Use waitid if avaliable Alistair Francis
2019-07-17 5:31 ` Florian Weimer
2019-07-19 17:52 ` Alistair Francis
2019-07-22 15:58 ` Florian Weimer
2019-07-22 21:06 ` Alistair Francis
2019-07-21 4:03 ` Rich Felker
2019-07-21 4:20 ` Rich Felker
2019-07-21 11:59 ` Eric W. Biederman
2019-07-21 23:00 ` Rich Felker
2019-07-21 7:57 ` Arnd Bergmann
2019-07-21 12:15 ` Eric W. Biederman
2019-07-21 12:28 ` Christian Brauner
2019-07-21 14:31 ` Arnd Bergmann
2019-07-21 15:45 ` Eric W. Biederman
2019-07-21 17:06 ` Arnd Bergmann
2019-07-21 17:22 ` Linus Torvalds
2019-07-21 21:40 ` Eric W. Biederman [this message]
2019-07-21 23:24 ` Rich Felker
2019-07-23 0:01 ` Eric W. Biederman
2019-07-23 8:12 ` Arnd Bergmann
2019-07-23 8:29 ` Christian Brauner
2019-07-23 8:45 ` Arnd Bergmann
2019-07-25 0:08 ` Alistair Francis
2019-07-25 4:40 ` Rich Felker
2019-07-25 13:23 ` Arnd Bergmann
2019-07-25 16:06 ` Christian Brauner
2019-07-25 17:14 ` Eric W. Biederman
2019-07-25 17:30 ` Christian Brauner
2019-08-13 22:25 ` Alistair Francis
2019-08-13 23:12 ` Rich Felker
2019-08-14 5:07 ` Christian Brauner
2019-08-14 11:40 ` [PATCH v1 0/1] waitid: process group enhancement christian.brauner
2019-08-14 11:40 ` [PATCH v1 1/1] waitid: Add support for waiting for the current process group christian.brauner
2019-08-14 12:29 ` Oleg Nesterov
2019-08-14 12:46 ` Christian Brauner
2019-08-14 12:50 ` Oleg Nesterov
2019-08-14 12:53 ` Christian Brauner
2019-08-14 13:10 ` [PATCH v2 0/1] waitid: process group enhancement Christian Brauner
2019-08-14 13:10 ` [PATCH v2 1/1] waitid: Add support for waiting for the current process group Christian Brauner
2019-08-14 14:20 ` Oleg Nesterov
2019-08-14 14:35 ` Christian Brauner
2019-08-14 15:27 ` Oleg Nesterov
2019-08-14 15:30 ` Christian Brauner
2019-08-14 15:46 ` [PATCH v3 0/1] waitid: process group enhancement Christian Brauner
2019-08-14 15:46 ` [PATCH v3 1/1] waitid: Add support for waiting for the current process group Christian Brauner
2019-08-14 16:09 ` Oleg Nesterov
2019-08-14 16:15 ` Christian Brauner
2019-08-14 16:34 ` Christian Brauner
2019-08-14 16:55 ` Rich Felker
2019-08-14 17:02 ` Christian Brauner
2019-08-14 17:06 ` Linus Torvalds
2019-08-14 18:00 ` Rich Felker
2019-08-14 20:50 ` Christian Brauner
2019-08-14 15:58 ` [PATCH v3 0/1] waitid: process group enhancement Rich Felker
2019-08-14 16:13 ` Christian Brauner
2019-07-26 23:39 ` [RFC v3 03/23] sysdeps/wait: Use waitid if avaliable Alistair Francis
2019-07-17 0:11 ` [RFC v3 08/23] RISC-V: define __NR_futex as __NR_futex_time64 for 32-bit Alistair Francis
2019-07-17 0:11 ` [RFC v3 01/23] sysdeps/nanosleep: Use clock_nanosleep_time64 if avaliable Alistair Francis
2019-07-17 5:16 ` Florian Weimer
2019-07-19 17:29 ` Alistair Francis
2019-07-20 14:24 ` Stepan Golosunov
2019-07-22 21:17 ` Alistair Francis
2019-07-17 0:11 ` [RFC v3 02/23] sysdeps/gettimeofday: Use clock_gettime64 " Alistair Francis
2019-07-17 7:09 ` Florian Weimer
2019-07-20 3:21 ` Rich Felker
2019-07-25 20:54 ` Joseph Myers
2019-07-17 12:43 ` Lukasz Majewski
2019-07-17 12:48 ` Lukasz Majewski
2019-07-19 22:29 ` Alistair Francis
2019-07-17 0:11 ` [RFC v3 04/23] sysdeps/clock_gettime: " Alistair Francis
2019-07-17 5:39 ` Florian Weimer
2019-07-17 8:04 ` Arnd Bergmann
2019-07-17 8:44 ` Florian Weimer
2019-07-17 9:10 ` Arnd Bergmann
2019-07-17 15:16 ` Florian Weimer
2019-07-18 7:39 ` Arnd Bergmann
2019-07-18 8:19 ` Florian Weimer
2019-07-18 9:15 ` Arnd Bergmann
2019-07-18 18:10 ` Adhemerval Zanella
2019-07-19 21:06 ` Alistair Francis
2019-07-17 7:03 ` Andreas Schwab
2019-07-17 12:37 ` Lukasz Majewski
2019-07-17 0:12 ` [RFC v3 12/23] RISC-V: define __vdso_clock_gettime as __vdso_clock_gettime64 for 32-bit Alistair Francis
2019-07-17 8:16 ` Arnd Bergmann
2019-07-19 17:19 ` Alistair Francis
2019-07-17 0:12 ` [RFC v3 10/23] RISC-V: define __NR_clock_getres as __NR_*_time64 " Alistair Francis
2019-07-17 0:12 ` [RFC v3 21/23] RISC-V: Fix llrint and llround missing exceptions on RV32 Alistair Francis
2019-07-17 12:22 ` Florian Weimer
2019-07-17 22:35 ` Alistair Francis
2019-07-17 0:12 ` [RFC v3 05/23] sysdeps/timespec_get: Use clock_gettime64 if avaliable Alistair Francis
2019-07-17 5:08 ` Florian Weimer
2019-07-17 7:59 ` Arnd Bergmann
2019-07-17 8:12 ` Florian Weimer
2019-07-17 8:23 ` Arnd Bergmann
2019-07-17 8:41 ` Florian Weimer
2019-07-17 8:54 ` Arnd Bergmann
2019-07-25 20:14 ` Joseph Myers
2019-07-17 12:23 ` Lukasz Majewski
2019-07-17 0:12 ` [RFC v3 13/23] RISC-V: Use 64-bit timespec in clock_gettime vdso calls Alistair Francis
2019-07-17 8:14 ` Arnd Bergmann
2019-07-17 0:12 ` [RFC v3 15/23] RISC-V: Add path of library directories for the 32-bit Alistair Francis
2019-07-17 12:20 ` Florian Weimer
2019-07-17 0:12 ` [RFC v3 11/23] RISC-V: define __vdso_clock_getres as __vdso_clock_getres_time64 for 32-bit Alistair Francis
2019-07-17 0:12 ` [RFC v3 14/23] RISC-V: Support dynamic loader for the 32-bit Alistair Francis
2019-07-17 0:12 ` [RFC v3 06/23] Documentation for the RISC-V 32-bit port Alistair Francis
2019-07-17 0:12 ` [RFC v3 18/23] RISC-V: Regenerate ULPs of RISC-V Alistair Francis
2019-07-17 0:12 ` [RFC v3 22/23] Add RISC-V 32-bit target to build-many-glibcs.py Alistair Francis
2019-07-17 0:12 ` [RFC v3 16/23] RISC-V: The ABI implementation for the 32-bit Alistair Francis
2019-07-17 0:12 ` [RFC v3 20/23] RISC-V: Build Infastructure " Alistair Francis
2019-07-17 0:12 ` [RFC v3 17/23] RISC-V: Hard float support for the 32 bit Alistair Francis
2019-07-17 0:12 ` [RFC v3 07/23] RISC-V: Use 64-bit time_t and off_t for RV32 and RV64 Alistair Francis
2019-07-17 8:27 ` Arnd Bergmann
2019-07-17 22:43 ` Alistair Francis
2019-07-18 7:41 ` Arnd Bergmann
2019-07-18 17:36 ` Alistair Francis
2019-07-19 6:44 ` Arnd Bergmann
2019-07-19 17:06 ` Alistair Francis
2019-07-17 0:12 ` [RFC v3 09/23] RISC-V: define __NR_* as __NR_*_time64/64 for 32-bit Alistair Francis
2019-07-17 0:12 ` [RFC v3 23/23] RISC-V: Use 64-bit vdso syscalls Alistair Francis
2019-07-17 5:33 ` Florian Weimer
2019-07-17 8:02 ` Arnd Bergmann
2019-07-17 22:27 ` Alistair Francis
2019-07-17 23:46 ` Alistair Francis
2019-07-18 0:05 ` Alistair Francis
2019-07-17 0:12 ` [RFC v3 19/23] RISC-V: Add ABI lists Alistair Francis
2019-07-19 17:18 ` [RFC v3 00/23] RISC-V glibc port for the 32-bit Alistair Francis
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