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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Sultan Alsawaf <sultan@kerneltoast.com>
Cc: "Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Theodore Ts'o" <tytso@mit.edu>,
	"Jonathan Neuschäfer" <j.neuschaefer@gmx.net>
Subject: Re: [PATCH RFC v1] random: do not take spinlocks in irq handler
Date: Sat, 5 Feb 2022 13:50:42 +0100	[thread overview]
Message-ID: <CAHmME9q1bdSeX5Eu+sNfJkch+odKTWFZ53Jo-ma98SDqouEF6w@mail.gmail.com> (raw)
In-Reply-To: <Yf320i+tVl6MXnD7@sultan-box.localdomain>

Hi Sultan,

On Sat, Feb 5, 2022 at 5:02 AM Sultan Alsawaf <sultan@kerneltoast.com> wrote:
> The __this_cpu_{ATOMIC_OP}() functions are for atomically performing a single
> per-CPU operation for the current CPU from contexts that permit CPU migration.
> Since this code is safe from CPU migrations (add_interrupt_randomness() runs in
> hardirq context), the atomic per-CPU helpers are unneeded. Instead of using
> __this_cpu_inc_return() and __this_cpu_or(), we can operate on the per-CPU
> pointer directly without any extra safety (e.g., `++fast_pool->count` can be
> used in place of `__this_cpu_inc_return(irq_randomness.count)`).

Oh, right, thanks. We're already in irq so we don't have to worried
about load,add,store being cut up in any way. I'll go back to simple
increments for v3.

Jason

      reply	other threads:[~2022-02-05 12:51 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-07 12:17 [PATCH 0/5] random: Add PREEMPT_RT support Sebastian Andrzej Siewior
2021-12-07 12:17 ` [PATCH 1/5] random: Remove unused irq_flags argument from add_interrupt_randomness() Sebastian Andrzej Siewior
2021-12-07 12:44   ` Wei Liu
2021-12-07 17:35   ` Jason A. Donenfeld
2021-12-07 12:17 ` [PATCH 2/5] irq: Remove unsued flags argument from __handle_irq_event_percpu() Sebastian Andrzej Siewior
2021-12-07 17:41   ` Jason A. Donenfeld
2021-12-11 22:39     ` Thomas Gleixner
2021-12-12 21:13       ` Jason A. Donenfeld
2021-12-07 12:17 ` [PATCH 3/5] random: Split add_interrupt_randomness() Sebastian Andrzej Siewior
2021-12-07 12:17 ` [PATCH 4/5] random: Move the fast_pool reset into the caller Sebastian Andrzej Siewior
2021-12-07 12:17 ` [PATCH 5/5] random: Defer processing of randomness on PREEMPT_RT Sebastian Andrzej Siewior
2021-12-07 18:14   ` Jason A. Donenfeld
2021-12-07 20:10     ` Sebastian Andrzej Siewior
2021-12-13 15:16       ` Sebastian Andrzej Siewior
2021-12-17  2:23       ` Herbert Xu
2021-12-17  9:00         ` Sebastian Andrzej Siewior
2021-12-18  3:24           ` Herbert Xu
2021-12-19  9:48             ` Sebastian Andrzej Siewior
2021-12-20  2:56               ` Herbert Xu
2021-12-20 14:38       ` Jason A. Donenfeld
2022-01-12 17:49         ` Sebastian Andrzej Siewior
2022-01-30 22:55           ` Jason A. Donenfeld
2022-01-31 16:33             ` Sebastian Andrzej Siewior
2022-02-04 15:31               ` [PATCH RFC v1] random: do not take spinlocks in irq handler Jason A. Donenfeld
2022-02-04 15:58                 ` Jason A. Donenfeld
2022-02-04 20:53                   ` Sebastian Andrzej Siewior
2022-02-04 20:47                 ` Sebastian Andrzej Siewior
2022-02-04 22:08                   ` Jason A. Donenfeld
2022-02-04 23:09                     ` [PATCH v2] random: defer fast pool mixing to worker Jason A. Donenfeld
2022-02-05  4:02                   ` [PATCH RFC v1] random: do not take spinlocks in irq handler Sultan Alsawaf
2022-02-05 12:50                     ` Jason A. Donenfeld [this message]

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