From: Oleg Nesterov <oleg@redhat.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Christian Brauner <christian@brauner.io>,
linux-kernel@vger.kernel.org, luto@amacapital.net,
rostedt@goodmis.org, dancol@google.com, sspatil@google.com,
jannh@google.com, surenb@google.com, timmurray@google.com,
Jonathan Kowalski <bl0pbl33p@gmail.com>,
torvalds@linux-foundation.org, kernel-team@android.com,
Andrew Morton <akpm@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Ingo Molnar <mingo@kernel.org>, Jann Horn <jann@thejh.net>,
linux-kselftest@vger.kernel.org, Michal Hocko <mhocko@suse.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Serge Hallyn <serge@hallyn.com>, Shuah Khan <shuah@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>, Thomas Gleixner <tgl>
Subject: Re: [PATCH v1 1/2] Add polling support to pidfd
Date: Mon, 29 Apr 2019 16:20:30 +0200 [thread overview]
Message-ID: <20190429142030.GA17715@redhat.com> (raw)
In-Reply-To: <20190429140245.GB233442@google.com>
On 04/29, Joel Fernandes wrote:
>
> However, in your code above, it is avoided because we get:
>
> Task A (poller) Task B (exiting task being polled)
> ------------ ----------------
> poll() called
> add_wait_queue()
> exit_state is set to non-zero
> read exit_state
> remove_wait_queue()
> wake_up_all()
just to clarify... No, sys_poll() path doesn't do remove_wait_queue() until
it returns to user mode, and that is why we can't race with set-exit_code +
wake_up().
pidfd_poll() can race with the exiting task, miss exit_code != 0, and return
zero. However, do_poll() won't block after that and pidfd_poll() will be called
again.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: oleg at redhat.com (Oleg Nesterov)
Subject: [PATCH v1 1/2] Add polling support to pidfd
Date: Mon, 29 Apr 2019 16:20:30 +0200 [thread overview]
Message-ID: <20190429142030.GA17715@redhat.com> (raw)
In-Reply-To: <20190429140245.GB233442@google.com>
On 04/29, Joel Fernandes wrote:
>
> However, in your code above, it is avoided because we get:
>
> Task A (poller) Task B (exiting task being polled)
> ------------ ----------------
> poll() called
> add_wait_queue()
> exit_state is set to non-zero
> read exit_state
> remove_wait_queue()
> wake_up_all()
just to clarify... No, sys_poll() path doesn't do remove_wait_queue() until
it returns to user mode, and that is why we can't race with set-exit_code +
wake_up().
pidfd_poll() can race with the exiting task, miss exit_code != 0, and return
zero. However, do_poll() won't block after that and pidfd_poll() will be called
again.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: oleg@redhat.com (Oleg Nesterov)
Subject: [PATCH v1 1/2] Add polling support to pidfd
Date: Mon, 29 Apr 2019 16:20:30 +0200 [thread overview]
Message-ID: <20190429142030.GA17715@redhat.com> (raw)
Message-ID: <20190429142030.IynvDqr69lr5xt-IoCFJ_k1ryS0spxCF7K6yGbK-BQo@z> (raw)
In-Reply-To: <20190429140245.GB233442@google.com>
On 04/29, Joel Fernandes wrote:
>
> However, in your code above, it is avoided because we get:
>
> Task A (poller) Task B (exiting task being polled)
> ------------ ----------------
> poll() called
> add_wait_queue()
> exit_state is set to non-zero
> read exit_state
> remove_wait_queue()
> wake_up_all()
just to clarify... No, sys_poll() path doesn't do remove_wait_queue() until
it returns to user mode, and that is why we can't race with set-exit_code +
wake_up().
pidfd_poll() can race with the exiting task, miss exit_code != 0, and return
zero. However, do_poll() won't block after that and pidfd_poll() will be called
again.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Christian Brauner <christian@brauner.io>,
linux-kernel@vger.kernel.org, luto@amacapital.net,
rostedt@goodmis.org, dancol@google.com, sspatil@google.com,
jannh@google.com, surenb@google.com, timmurray@google.com,
Jonathan Kowalski <bl0pbl33p@gmail.com>,
torvalds@linux-foundation.org, kernel-team@android.com,
Andrew Morton <akpm@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Ingo Molnar <mingo@kernel.org>, Jann Horn <jann@thejh.net>,
linux-kselftest@vger.kernel.org, Michal Hocko <mhocko@suse.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Serge Hallyn <serge@hallyn.com>, Shuah Khan <shuah@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Thomas Gleixner <tglx@linutronix.de>,
Tycho Andersen <tycho@tycho.ws>,
viro@zeniv.linux.org.uk, linux-api@vger.kernel.org
Subject: Re: [PATCH v1 1/2] Add polling support to pidfd
Date: Mon, 29 Apr 2019 16:20:30 +0200 [thread overview]
Message-ID: <20190429142030.GA17715@redhat.com> (raw)
In-Reply-To: <20190429140245.GB233442@google.com>
On 04/29, Joel Fernandes wrote:
>
> However, in your code above, it is avoided because we get:
>
> Task A (poller) Task B (exiting task being polled)
> ------------ ----------------
> poll() called
> add_wait_queue()
> exit_state is set to non-zero
> read exit_state
> remove_wait_queue()
> wake_up_all()
just to clarify... No, sys_poll() path doesn't do remove_wait_queue() until
it returns to user mode, and that is why we can't race with set-exit_code +
wake_up().
pidfd_poll() can race with the exiting task, miss exit_code != 0, and return
zero. However, do_poll() won't block after that and pidfd_poll() will be called
again.
Oleg.
next prev parent reply other threads:[~2019-04-29 14:20 UTC|newest]
Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-25 19:00 [PATCH v1 1/2] Add polling support to pidfd joel
2019-04-25 19:00 ` Joel Fernandes (Google)
2019-04-25 19:00 ` Joel Fernandes (Google)
2019-04-25 19:00 ` [PATCH v1 2/2] Add selftests for pidfd polling joel
2019-04-25 19:00 ` Joel Fernandes (Google)
2019-04-25 19:00 ` Joel Fernandes (Google)
2019-04-25 20:00 ` tycho
2019-04-25 20:00 ` Tycho Andersen
2019-04-25 20:00 ` Tycho Andersen
2019-04-26 13:47 ` joel
2019-04-26 13:47 ` Joel Fernandes
2019-04-26 13:47 ` Joel Fernandes
2019-04-25 21:29 ` christian
2019-04-25 21:29 ` Christian Brauner
2019-04-25 21:29 ` Christian Brauner
2019-04-25 22:07 ` dancol
2019-04-25 22:07 ` Daniel Colascione
2019-04-25 22:07 ` Daniel Colascione
2019-04-26 17:26 ` joel
2019-04-26 17:26 ` Joel Fernandes
2019-04-26 17:26 ` Joel Fernandes
2019-04-26 19:35 ` dancol
2019-04-26 19:35 ` Daniel Colascione
2019-04-26 19:35 ` Daniel Colascione
2019-04-26 20:31 ` joel
2019-04-26 20:31 ` Joel Fernandes
2019-04-26 20:31 ` Joel Fernandes
2019-04-26 13:42 ` joel
2019-04-26 13:42 ` Joel Fernandes
2019-04-26 13:42 ` Joel Fernandes
2019-04-25 22:24 ` [PATCH v1 1/2] Add polling support to pidfd Christian Brauner
2019-04-25 22:24 ` Christian Brauner
2019-04-25 22:24 ` Christian Brauner
2019-04-25 22:24 ` christian
2019-04-26 14:23 ` Joel Fernandes
2019-04-26 14:23 ` Joel Fernandes
2019-04-26 14:23 ` Joel Fernandes
2019-04-26 14:23 ` joel
2019-04-26 15:21 ` Christian Brauner
2019-04-26 15:21 ` Christian Brauner
2019-04-26 15:21 ` Christian Brauner
2019-04-26 15:21 ` christian
2019-04-26 15:31 ` Christian Brauner
2019-04-26 15:31 ` Christian Brauner
2019-04-26 15:31 ` Christian Brauner
2019-04-26 15:31 ` christian
2019-04-28 16:24 ` Oleg Nesterov
2019-04-28 16:24 ` Oleg Nesterov
2019-04-28 16:24 ` Oleg Nesterov
2019-04-28 16:24 ` oleg
2019-04-29 14:02 ` Joel Fernandes
2019-04-29 14:02 ` Joel Fernandes
2019-04-29 14:02 ` Joel Fernandes
2019-04-29 14:02 ` joel
2019-04-29 14:07 ` Joel Fernandes
2019-04-29 14:07 ` Joel Fernandes
2019-04-29 14:07 ` Joel Fernandes
2019-04-29 14:07 ` joel
2019-04-29 14:25 ` Oleg Nesterov
2019-04-29 14:25 ` Oleg Nesterov
2019-04-29 14:25 ` Oleg Nesterov
2019-04-29 14:25 ` oleg
2019-04-29 14:20 ` Oleg Nesterov [this message]
2019-04-29 14:20 ` Oleg Nesterov
2019-04-29 14:20 ` Oleg Nesterov
2019-04-29 14:20 ` oleg
2019-04-29 16:32 ` Joel Fernandes
2019-04-29 16:32 ` Joel Fernandes
2019-04-29 16:32 ` Joel Fernandes
2019-04-29 16:32 ` joel
2019-04-30 11:53 ` Oleg Nesterov
2019-04-30 11:53 ` Oleg Nesterov
2019-04-30 11:53 ` Oleg Nesterov
2019-04-30 11:53 ` oleg
2019-04-30 12:07 ` Oleg Nesterov
2019-04-30 12:07 ` Oleg Nesterov
2019-04-30 12:07 ` Oleg Nesterov
2019-04-30 12:07 ` oleg
2019-04-30 15:49 ` Joel Fernandes
2019-04-30 15:49 ` Joel Fernandes
2019-04-30 15:49 ` Joel Fernandes
2019-04-30 15:49 ` joel
2019-04-26 14:58 ` christian
2019-04-26 14:58 ` Christian Brauner
2019-04-26 14:58 ` Christian Brauner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190429142030.GA17715@redhat.com \
--to=oleg@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=bl0pbl33p@gmail.com \
--cc=christian@brauner.io \
--cc=dancol@google.com \
--cc=ebiederm@xmission.com \
--cc=gregkh@linuxfoundation.org \
--cc=jann@thejh.net \
--cc=jannh@google.com \
--cc=joel@joelfernandes.org \
--cc=kernel-team@android.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=mhocko@suse.com \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=serge@hallyn.com \
--cc=sfr@canb.auug.org.au \
--cc=shuah@kernel.org \
--cc=sspatil@google.com \
--cc=surenb@google.com \
--cc=timmurray@google.com \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.