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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [patch 0/2] x86/fpu: Make fpu_lock() RT compliant
Date: Tue, 27 Oct 2020 11:09:49 +0100	[thread overview]
Message-ID: <20201027100949.181320853@linutronix.de> (raw)

FPU serialization uses

    preempt_disable(); local_bh_disable();

which is silly because local_bh_disable() implicitly disables
preemption. So this can be reduced to local_bh_disable().

But this does not work on RT kernels because local_bh_disable() only
serializes bottom half related processing via a local lock, but does not
disable preemption.

On RT kernels preempt_disable() is the right choice because on RT bottom
half processing is always in thread context, so preempt_disable()
implicitly protects against bottom half processing there.

Thanks,

	tglx


             reply	other threads:[~2020-10-27 10:16 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-27 10:09 Thomas Gleixner [this message]
2020-10-27 10:09 ` [patch 1/2] x86/fpu: Simplify fpregs_[un]lock() Thomas Gleixner
2020-11-11 13:36   ` [tip: x86/fpu] " tip-bot2 for Thomas Gleixner
2020-10-27 10:09 ` [patch 2/2] x86/fpu: Make kernel FPU protection RT friendly Thomas Gleixner
2020-10-27 10:42   ` Sebastian Andrzej Siewior
2020-11-11 13:36   ` [tip: x86/fpu] " tip-bot2 for Thomas Gleixner

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