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From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
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	Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [patch 00/13] preempt: Make preempt count unconditional
Date: Wed, 16 Sep 2020 11:32:00 -0700
Message-ID: <CAHk-=wjsMycgMHJrCmeetR3r+K5bpSRtmVWfd8iaoQCYd_VYAg@mail.gmail.com> (raw)
In-Reply-To: <20200916152956.GV29330@paulmck-ThinkPad-P72>

On Wed, Sep 16, 2020 at 8:29 AM Paul E. McKenney <paulmck@kernel.org> wrote:
>
> All fair, but some of us need to write code that must handle being
> invoked from a wide variety of contexts.

Note that I think that core functionality is different from random drivers.

Of course core code can (and will) look at things like

        if (in_interrupt())
            .. schedule work asynchronously ..

because core code ends up being called from odd places, and code like
that is expected to have understanding of the rules it plays with.

But something like RCU is a very different beast from some "walk the
scatter-gather list" code.

RCU does its work in the background, and works with lots of different
things. And it's so core and used everywhere that it knows about these
things. I mean, we literally have special code explicitly to let RCU
know "we entered kernel context now".

But something like a driver list walking thing should not be doing
different things behind peoples back depending on whether they hold
spinlocks or not. It should either just work regardless, or there
should be a flag (or special interface) for the "you're being called
in a crtitical region".

Because dynamically changing behavior really is very confusing.

               Linus
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  reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-14 20:42 Thomas Gleixner
2020-09-14 20:42 ` [patch 01/13] lib/debug: Remove pointless ARCH_NO_PREEMPT dependencies Thomas Gleixner
2020-09-14 20:42 ` [patch 02/13] preempt: Make preempt count unconditional Thomas Gleixner
2020-09-14 20:42 ` [patch 03/13] preempt: Clenaup PREEMPT_COUNT leftovers Thomas Gleixner
2020-09-14 20:42 ` [patch 04/13] lockdep: " Thomas Gleixner
2020-09-15 16:11   ` Will Deacon
2020-09-14 20:42 ` [patch 05/13] mm/pagemap: " Thomas Gleixner
2020-09-14 20:42 ` [patch 06/13] locking/bitspinlock: " Thomas Gleixner
2020-09-15 16:10   ` Will Deacon
2020-09-14 20:42 ` [patch 07/13] uaccess: " Thomas Gleixner
2020-09-14 20:42 ` [patch 08/13] sched: " Thomas Gleixner
2020-09-14 20:42 ` [patch 09/13] ARM: " Thomas Gleixner
2020-09-14 20:42 ` [patch 10/13] xtensa: " Thomas Gleixner
2020-09-14 20:42 ` [patch 11/13] drm/i915: " Thomas Gleixner
2020-09-14 20:42 ` [patch 12/13] rcutorture: " Thomas Gleixner
2020-09-14 20:42 ` [patch 13/13] preempt: Remove PREEMPT_COUNT from Kconfig Thomas Gleixner
2020-09-14 20:54 ` [patch 00/13] preempt: Make preempt count unconditional Steven Rostedt
2020-09-14 20:59 ` Linus Torvalds
2020-09-14 21:55   ` Thomas Gleixner
2020-09-14 22:24     ` Linus Torvalds
2020-09-14 22:37       ` Linus Torvalds
2020-09-15  3:21         ` [PATCH] crypto: lib/chacha20poly1305 - Set SG_MITER_ATOMIC unconditionally Herbert Xu
2020-09-15  6:20         ` [patch 00/13] preempt: Make preempt count unconditional Ard Biesheuvel
2020-09-15  6:22           ` Herbert Xu
2020-09-15  6:39             ` Linus Torvalds
     [not found]               ` <87een35woz.fsf@nanos.tec.linutronix.de>
2020-09-15 17:29                 ` Linus Torvalds
     [not found]       ` <87bli75t7v.fsf@nanos.tec.linutronix.de>
2020-09-15 17:35         ` Linus Torvalds
2020-09-15 19:57           ` Thomas Gleixner
2020-09-16 18:34             ` Linus Torvalds
2020-09-16  7:37           ` Daniel Vetter
2020-09-16 15:29             ` Paul E. McKenney
2020-09-16 18:32               ` Linus Torvalds [this message]
2020-09-16 20:43                 ` Paul E. McKenney
2020-09-17  6:38                 ` Ard Biesheuvel
2020-09-16 20:29               ` Daniel Vetter
2020-09-16 20:58                 ` Paul E. McKenney
2020-09-16 21:43                   ` Daniel Vetter
2020-09-16 22:39                     ` Paul E. McKenney
2020-09-17  7:52                       ` Daniel Vetter
2020-09-17 16:28                         ` Paul E. McKenney
2020-09-29  8:19                     ` Michal Hocko
2020-09-29  8:19                       ` Michal Hocko
2020-09-29  8:20                       ` Michal Hocko
2020-09-29  8:21                       ` Michal Hocko
2020-09-29  8:23                       ` Michal Hocko
2020-09-29  9:00                       ` Daniel Vetter
2020-09-29 14:54                         ` Michal Hocko
2020-09-16 19:23     ` Matthew Wilcox
2020-09-16 20:48       ` Paul E. McKenney
2020-09-15 17:25   ` Paul E. McKenney

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