linux-kernel - [PATCH rcu 0/4] NMI-safe SRCU reader API

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Message-ID: <20220921144620.GA1200846@paulmck-ThinkPad-P17-Gen-1>
Date:   Wed, 21 Sep 2022 07:46:20 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, tglx@...utronix.de, john.ogness@...utronix.de,
        pmladek@...e.com
Subject: [PATCH rcu 0/4] NMI-safe SRCU reader API

Hello!

This RFC series provides an NMI-safe SRCU reader API in the guise
of srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe().  A given
srcu_struct structure must use either the traditional srcu_read_lock()
and srcu_read_unlock() API or the new _nmisafe() API:  Mixing and matching
is not permitted.  So much so that kernels built with CONFIG_PROVE_RCU=y
will complain if you try it.

The reason for this restriction is that I have yet to find a use case
that is not a accident waiting to happen.  And if free intermixing
were permitted, it is pretty much a given that someone somewhere will
get confused and use srcu_read_lock_nmisafe() within NMI handlers and
srcu_read_lock() elsewhere, which will not (repeat, NOT) provide NMI
safety.

The series is as follows:

1.	Convert ->srcu_lock_count and ->srcu_unlock_count to atomic.

2.	Create and srcu_read_lock_nmisafe() and
	srcu_read_unlock_nmisafe().

3.	Check for consistent per-CPU per-srcu_struct NMI safety.

4.	Check for consistent global per-srcu_struct NMI safety.

						Thanx, Paul

------------------------------------------------------------------------

 b/include/linux/srcu.h     |   37 ++++++++++++++++++++
 b/include/linux/srcutiny.h |   11 ++++++
 b/include/linux/srcutree.h |    4 +-
 b/kernel/rcu/Kconfig       |    3 +
 b/kernel/rcu/rcutorture.c  |   11 ++++--
 b/kernel/rcu/srcutree.c    |   24 ++++++-------
 include/linux/srcu.h       |    4 +-
 include/linux/srcutiny.h   |    4 +-
 include/linux/srcutree.h   |   12 +++++-
 kernel/rcu/srcutree.c      |   82 +++++++++++++++++++++++++++++++++++++++------
 10 files changed, 160 insertions(+), 32 deletions(-)