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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-kernel@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Will Deacon <will@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 0/8] Introduce local_lock()
Date: Tue, 19 May 2020 22:19:04 +0200	[thread overview]
Message-ID: <20200519201912.1564477-1-bigeasy@linutronix.de> (raw)

preempt_disable() and local_irq_disable/save() are in principle per CPU big
kernel locks. This has several downsides:

  - The protection scope is unknown

  - Violation of protection rules is hard to detect by instrumentation

  - For PREEMPT_RT such sections, unless in low level critical code, can
    violate the preemptability constraints.

To address this PREEMPT_RT introduced the concept of local_locks which are
strictly per CPU.

The lock operations map to preempt_disable(), local_irq_disable/save() and
the enabling counterparts on non RT enabled kernels.

If lockdep is enabled local locks gain a lock map which tracks the usage
context. This will catch cases where an area is protected by
preempt_disable() but the access also happens from interrupt context. local
locks have identified quite a few such issues over the years, the most
recent example is:

  b7d5dc21072cd ("random: add a spinlock_t to struct batched_entropy")

Aside of the lockdep coverage this also improves code readability as it
precisely annotates the protection scope.

PREEMPT_RT substitutes these local locks with 'sleeping' spinlocks to
protect such sections while maintaining preemtability and CPU locality.

The following series introduces the infrastructure including
documentation and provides a couple of examples how they are used to
adjust code to be RT ready.

Sebastian



             reply	other threads:[~2020-05-19 20:19 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-19 20:19 Sebastian Andrzej Siewior [this message]
2020-05-19 20:19 ` [PATCH 1/8] locking: " Sebastian Andrzej Siewior
2020-05-20 12:04   ` Peter Zijlstra
2020-05-22 11:05     ` Sebastian Andrzej Siewior
2020-05-22 13:01       ` Peter Zijlstra
2020-05-19 20:19 ` [PATCH 2/8] radix-tree: Use local_lock for protection Sebastian Andrzej Siewior
2020-05-19 20:45   ` Matthew Wilcox
2020-05-19 20:54     ` Steven Rostedt
2020-05-20  2:05       ` Matthew Wilcox
2020-05-20 10:13         ` Sebastian Andrzej Siewior
2020-05-20 10:21   ` Peter Zijlstra
2020-05-20 12:28     ` Thomas Gleixner
2020-05-19 20:19 ` [PATCH 3/8] srcu: Use local_lock() for per-CPU struct srcu_data access Sebastian Andrzej Siewior
2020-05-20 10:24   ` Peter Zijlstra
2020-05-20 12:06     ` Sebastian Andrzej Siewior
2020-05-20 13:27       ` Peter Zijlstra
2020-05-20 17:42       ` Joel Fernandes
2020-05-20 18:28         ` Sebastian Andrzej Siewior
2020-05-20 18:35           ` Peter Zijlstra
2020-05-20 18:44             ` Joel Fernandes
2020-05-20 18:50               ` Uladzislau Rezki
2020-05-20 18:59           ` Joel Fernandes
2020-05-20 18:43       ` Paul E. McKenney
2020-05-22 15:12         ` Sebastian Andrzej Siewior
2020-05-22 17:39           ` Paul E. McKenney
2020-05-23 15:08             ` Sebastian Andrzej Siewior
2020-05-23 16:59               ` Paul E. McKenney
2020-05-24 19:03               ` Sebastian Andrzej Siewior
2020-05-25  3:27                 ` Paul E. McKenney
2020-05-26 13:41                   ` [PATCH] srcu: Avoid local_irq_save() before acquiring spinlock_t Sebastian Andrzej Siewior
2020-05-26 16:16                     ` Paul E. McKenney
2020-05-26 16:31                       ` Sebastian Andrzej Siewior
2020-05-19 20:19 ` [PATCH 4/8] mm/swap: Use local_lock for protection Sebastian Andrzej Siewior
2020-05-19 23:58   ` Andrew Morton
2020-05-20  2:17     ` Matthew Wilcox
2020-05-20 10:53   ` Peter Zijlstra
2020-05-19 20:19 ` [PATCH 5/8] squashfs: make use of local lock in multi_cpu decompressor Sebastian Andrzej Siewior
2020-05-20 10:56   ` Peter Zijlstra
2020-05-19 20:19 ` [PATCH 6/8] connector/cn_proc: Protect send_msg() with a local lock Sebastian Andrzej Siewior
2020-05-20 11:03   ` Peter Zijlstra
2020-05-19 20:19 ` [PATCH 7/8] zram: Use local lock to protect per-CPU data Sebastian Andrzej Siewior
2020-05-20 11:07   ` Peter Zijlstra
2020-05-19 20:19 ` [PATCH 8/8] mm/zswap: " Sebastian Andrzej Siewior
2020-05-19 21:46   ` Song Bao Hua
2020-05-20 10:26     ` Sebastian Andrzej Siewior
2020-05-20 11:13       ` Song Bao Hua
2020-05-20 11:57         ` Sebastian Andrzej Siewior
2020-05-20 12:01           ` Song Bao Hua

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