linux-ext4 - [PATCH 0/7] jbd2: Bit spinlock conversions

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Date:   Fri,  2 Aug 2019 17:13:49 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ted Tso <tytso@....edu>
Cc:     <linux-ext4@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Julia Cartwright <julia@...com>, Jan Kara <jack@...e.cz>
Subject: [PATCH 0/7] jbd2: Bit spinlock conversions

Hello,

This series is derived from Thomas' series to get rid of bit spinlocks in
buffer head code. These patches convert BH_State bit spinlock to an ordinary
spinlock inside struct journal_head and somewhat reduce the critical section
under BH_JournalHead bit spinlock so that it is fine for RT. 

Motivation from original Thomas' series:

Bit spinlocks are problematic if PREEMPT_RT is enabled. They disable
preemption, which is undesired for latency reasons and breaks when regular
spinlocks are taken within the bit_spinlock locked region because regular
spinlocks are converted to 'sleeping spinlocks' on RT.

Bit spinlocks are also not covered by lock debugging, e.g. lockdep. With
the spinlock substitution in place, they can be exposed via a new config
switch: CONFIG_DEBUG_BIT_SPINLOCKS.

WRT patch routing: Since these are non-trivial changes to JBD2 and independent
of the rest of the series from Thomas, I think it would be safest to route
them through ext4 tree where they get most testing. Thoughts?

								Honza