From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [GIT pull] sched/core for v5.16-rc1
Date: Tue, 2 Nov 2021 09:54:02 +0100 [thread overview]
Message-ID: <YYD8qi/GsTrTlPMh@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAHk-=whEbr+0ZSRMkQ1wqLCeBEiK7o2-Hm=55aTBpdeVxnFbVQ@mail.gmail.com>
On Mon, Nov 01, 2021 at 02:01:13PM -0700, Linus Torvalds wrote:
> On Sun, Oct 31, 2021 at 6:16 PM Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > - Make wchan() more robust and work with all kind of unwinders by
> > enforcing that the task stays blocked while unwinding is in progress.
>
> Ugh. This not-very-important data is protected by a rather core lock.
>
> Is this yet another example of "unwinding is so fragile that it can
> screw up unless we take a lock that is seriously overkill for a not
> very important operation"?
>
> Unwinders that need locks because they can do bad things if they are
> working on unstable data are EVIL and WRONG.
Because of that :/ The eventual plan was to implement wchan in core code
using the 'regular' stack unwinding functions we have, the diffstats are
nice, but the unwinders not so. Also see my other reply.
https://lkml.kernel.org/r/20211022152104.487919043@infradead.org
> I guess I don't care too much about the pi_lock, and the actual
> unwinding is hopefully done on tasks that don't care about it, but
> this smells suspicious to me.
You do in fact care about pi_lock. The name is very wrong these days
(and I've been very tardy with renaming it because I can't seem to come
up with a good name).
It is in fact the core lock involved with regular wakeups. The lock was
initially PI only, but it got co-opted into common scheduler use a fair
number of years ago. These days it serializes pretty much all per-task
scheduling state, not only the pi-chain. So perhaps I should do:
s/pi_lock/sched_lock/ ?
next prev parent reply other threads:[~2021-11-02 8:56 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-01 1:15 [GIT pull] irq/core for v5.16-rc1 Thomas Gleixner
2021-11-01 1:15 ` [GIT pull] locking/core " Thomas Gleixner
2021-11-01 21:20 ` pr-tracker-bot
2021-11-01 1:16 ` [GIT pull] objtool/core " Thomas Gleixner
2021-11-01 20:44 ` Linus Torvalds
2021-11-02 8:00 ` Peter Zijlstra
2021-11-02 8:06 ` Borislav Petkov
2021-11-02 9:05 ` Stackleak vs noinstr (Was: [GIT pull] objtool/core for v5.16-rc1) Peter Zijlstra
2021-11-02 10:03 ` Peter Zijlstra
2021-11-02 17:50 ` Linus Torvalds
2021-11-02 21:18 ` Borislav Petkov
2021-11-03 7:18 ` Alexander Popov
2021-11-03 8:19 ` Peter Zijlstra
2022-02-01 23:59 ` Kees Cook
2021-11-01 21:20 ` [GIT pull] objtool/core for v5.16-rc1 pr-tracker-bot
2021-11-01 1:16 ` [GIT pull] perf/core " Thomas Gleixner
2021-11-01 21:20 ` pr-tracker-bot
2021-11-01 1:16 ` [GIT pull] sched/core " Thomas Gleixner
2021-11-01 21:01 ` Linus Torvalds
2021-11-01 21:27 ` Linus Torvalds
2021-11-02 8:41 ` Peter Zijlstra
2021-11-03 13:52 ` Mark Rutland
2021-11-03 16:23 ` Linus Torvalds
2021-11-02 8:54 ` Peter Zijlstra [this message]
2021-11-01 21:20 ` pr-tracker-bot
2021-11-01 1:16 ` [GIT pull] timers/core " Thomas Gleixner
2021-11-01 21:20 ` pr-tracker-bot
2021-11-01 1:16 ` [GIT pull] x86/apic " Thomas Gleixner
2021-11-01 21:20 ` pr-tracker-bot
2021-11-01 1:52 ` [GIT pull RESEND] x86/fpu " Thomas Gleixner
2021-11-01 21:20 ` pr-tracker-bot
2021-11-01 21:19 ` [GIT pull] irq/core " pr-tracker-bot
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