From: Christian Brauner <christian.brauner@ubuntu.com>
To: Rich Felker <dalias@libc.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
linux-kernel@vger.kernel.org, libc-alpha@sourceware.org,
alistair23@gmail.com, ebiederm@xmission.com, arnd@arndb.de,
torvalds@linux-foundation.org, adhemerval.zanella@linaro.org,
fweimer@redhat.com, palmer@sifive.com, macro@wdc.com,
zongbox@gmail.com, akpm@linux-foundation.org,
viro@zeniv.linux.org.uk, hpa@zytor.com
Subject: Re: [PATCH v3 1/1] waitid: Add support for waiting for the current process group
Date: Wed, 14 Aug 2019 17:02:00 -0000 [thread overview]
Message-ID: <20190814170200.kqkygob7yo5hciau@wittgenstein> (raw)
In-Reply-To: <20190814165501.GJ9017@brightrain.aerifal.cx>
On Wed, Aug 14, 2019 at 12:55:01PM -0400, Rich Felker wrote:
> On Wed, Aug 14, 2019 at 06:34:44PM +0200, Christian Brauner wrote:
> > On Wed, Aug 14, 2019 at 06:15:17PM +0200, Christian Brauner wrote:
> > > On Wed, Aug 14, 2019 at 06:09:17PM +0200, Oleg Nesterov wrote:
> > > > On 08/14, Christian Brauner wrote:
> > > > >
> > > > > and a signal could come in between the system call that
> > > > > retrieved the process gorup and the call to waitid that changes the
> > > > ^^^^^
> > > > > current process group.
> > > >
> > > > I noticed this typo only because I spent 2 minutes or more trying to
> > > > understand this sentence ;) But yes, a signal handler or another thread
> > >
> > > I'll try to rewrite it. :)
> >
> > Ok, here's what I changed it to:
> >
> > It was recently discovered that the linux version of waitid is not a
> > superset of the other wait functions because it does not include
> > support for waiting for the current process group. This has two
> > downsides:
> > 1. An extra system call is needed to get the current process group.
> > 2. After the current process group is received and before it is passed
> > to waitid a signal could arrive causing the current process group to change.
>
> I don't think "downsides" sufficiently conveys that this is hard
> breakage of a requirement for waitpid. How about something like the
> following?
>
> "It was recently discovered that the linux version of waitid is not a
> superset of the other wait functions because it does not include
> support for waiting for the current process group. Userspace cannot
> simply emulate this functionality with an additional getpgid syscall
> due to inherent race conditions that violate the async-signal safety
> requirements for waitpid."
I like the rather specific example in there. How about we add that after
this section like so:
It was recently discovered that the linux version of waitid is not a
superset of the other wait functions because it does not include
support for waiting for the current process group. This has two
downsides:
1. An extra system call is needed to get the current process group.
2. After the current process group is received and before it is passed
to waitid a signal could arrive causing the current process group to change.
Such inherent race-conditions as mentioned in 2. make it impossible for
userspace to emulate this functionaly and thus violate the async-signal
safety requirements for waitpid.
Christian
next prev parent reply other threads:[~2019-08-14 17:02 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
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 [this message]
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 04/23] sysdeps/clock_gettime: Use clock_gettime64 " 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 0:11 ` [RFC v3 02/23] sysdeps/gettimeofday: " 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 0:12 ` [RFC v3 05/23] sysdeps/timespec_get: " 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 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 10/23] RISC-V: define __NR_clock_getres as __NR_*_time64 for 32-bit Alistair Francis
2019-07-17 0:12 ` [RFC v3 12/23] RISC-V: define __vdso_clock_gettime as __vdso_clock_gettime64 " Alistair Francis
2019-07-17 8:16 ` Arnd Bergmann
2019-07-19 17:19 ` 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 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 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 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 18/23] RISC-V: Regenerate ULPs of RISC-V 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 16/23] RISC-V: The ABI implementation for the 32-bit 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 20/23] RISC-V: Build Infastructure 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 17/23] RISC-V: Hard float support for the 32 bit 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 19/23] RISC-V: Add ABI lists 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
2019-07-19 17:18 ` [RFC v3 00/23] RISC-V glibc port for the 32-bit Alistair Francis
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