From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Adhemerval Zanella <adhemerval.zanella@linaro.org>,
Lukasz Majewski <lukma@denx.de>,
Florian Weimer <fweimer@redhat.com>,
Carlos O'Donell <carlos@redhat.com>,
"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Ingo Molnar <mingo@kernel.org>,
Darren Hart <dvhart@infradead.org>,
Andrei Vagin <avagin@gmail.com>,
Kurt Kanzenbach <kurt@linutronix.de>
Subject: [patch 0/6] futex: Bugfixes and FUTEX_LOCK_PI2
Date: Thu, 22 Apr 2021 21:44:17 +0200 [thread overview]
Message-ID: <20210422194417.866740847@linutronix.de> (raw)
The following series started off looking into supporting selectable clocks
for FUTEX_LOCK_PI which is hardcoded to CLOCK_REALTIME and cannot be
changed.
On the way I found two bugs related to the timeout handling:
- The allowance for FUTEX_WAIT to use FUTEX_CLOCK_REALTIME is broken and
never worked.
- The recent time namespace support wreckaged FUTEX_LOCK_PI timeouts when
the task belongs to a namespace which has an CLOCK_MONOTONIC offset.
Both should have been caught by that Gleixner dude when merging them,
but it seems he's getting old.
Not having a selectable clock for PI futexes is inconsistent because all
other interfaces have it. Unfortunately this was figured out by glibc folks
quite some time ago, but nobody told us :(
The nasty hack to support it would be to treat FUTEX_CLOCK_REALTIME inverse
for FUTEX_LOCK_PI, but that's a horrible idea. Adding a new flag to the
futex op, i.e. FUTEX_CLOCK_MONOTONIC would be possible, but that's yet
another variant which makes is harder for libraries to have a consistent
clock selection handling.
So I went the way to let FUTEX_LOCK_PI alone and to add FUTEX_LOCK_PI2
which handles the clocks the same way as the other operands.
Thoughts?
The series is also available from git:
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git futex
Thanks,
tglx
---
include/uapi/linux/futex.h | 1
kernel/futex.c | 89 +++++++++++++++++++++++----------------------
2 files changed, 47 insertions(+), 43 deletions(-)
next reply other threads:[~2021-04-22 20:29 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 19:44 Thomas Gleixner [this message]
2021-04-22 19:44 ` [patch 1/6] Revert 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op") Thomas Gleixner
2021-05-06 18:14 ` [tip: locking/urgent] " tip-bot2 for Thomas Gleixner
2021-04-22 19:44 ` [patch 2/6] futex: Do not apply time namespace adjustment on FUTEX_LOCK_PI Thomas Gleixner
2021-05-06 18:14 ` [tip: locking/urgent] " tip-bot2 for Thomas Gleixner
2021-04-22 19:44 ` [patch 3/6] futex: Get rid of the val2 conditional dance Thomas Gleixner
2021-04-23 21:40 ` André Almeida
2021-04-23 22:34 ` Thomas Gleixner
2021-04-23 23:21 ` André Almeida
2021-05-06 18:20 ` [tip: locking/urgent] " tip-bot2 for Thomas Gleixner
2021-04-22 19:44 ` [patch 4/6] futex: Make syscall entry points less convoluted Thomas Gleixner
2021-05-06 18:20 ` [tip: locking/urgent] " tip-bot2 for Thomas Gleixner
2021-04-22 19:44 ` [patch 5/6] futex: Prepare futex_lock_pi() for runtime clock selection Thomas Gleixner
2021-04-23 9:34 ` Lukasz Majewski
2021-04-23 10:08 ` Thomas Gleixner
2021-06-23 8:19 ` [tip: locking/core] " tip-bot2 for Thomas Gleixner
2021-04-22 19:44 ` [patch 6/6] futex: Provide FUTEX_LOCK_PI2 to support " Thomas Gleixner
2021-04-23 22:20 ` André Almeida
2021-04-23 22:36 ` Thomas Gleixner
2021-06-23 8:19 ` [tip: locking/core] " tip-bot2 for Thomas Gleixner
2021-05-05 12:59 ` [patch 0/6] futex: Bugfixes and FUTEX_LOCK_PI2 Peter Zijlstra
2021-05-05 13:51 ` Kurt Kanzenbach
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