From: Michael Ellerman <mpe@ellerman.id.au>
To: Benjamin Gray <bgray@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
Cc: Jordan Niethe <jniethe5@gmail.com>
Subject: Re: [PATCH] powerpc/powermac: Use early_* IO variants in via_calibrate_decr
Date: Wed, 02 Aug 2023 23:10:10 +1000 [thread overview]
Message-ID: <87y1itzj2l.fsf@mail.lhotse> (raw)
In-Reply-To: <643ebc8519d22e0ed869989490f39780c1bde09d.camel@linux.ibm.com>
Benjamin Gray <bgray@linux.ibm.com> writes:
> On Thu, 2023-07-06 at 11:08 +1000, Benjamin Gray wrote:
>> The issue is pre-existing, but is surfaced by commit 721255b9826b
>> ("genirq: Use a maple tree for interrupt descriptor management").
>> It's not clear to me why this causes it to surface.
>
> From the thread chain in [1], it looks like the maple tree
> implementation just has different allocation behaviour, which follows a
> pre-existing code path to kmem_cache_alloc_bulk(), which
> unconditionally enables interrupts.
That was a bug that was fixed before the series was merged.
See:
f5451547b831 ("mm, slab/slub: Ensure kmem_cache_alloc_bulk() is available early")
It looks like the trigger here is that the maple tree code uses
call_rcu() in ma_free_rcu(), and call_rcu() can cause TIF_NEED_RESCHED
to be set, which causes cond_resched() to actually reschedule, enabling
interrupts.
cheers
> (thanks Jordan Niethe for finding this thread)
>
> [1]: https://lore.kernel.org/all/87o7qdzfay.ffs@tglx/
prev parent reply other threads:[~2023-08-02 13:11 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-06 1:08 [PATCH] powerpc/powermac: Use early_* IO variants in via_calibrate_decr Benjamin Gray
2023-07-06 4:37 ` Christophe Leroy
2023-07-07 2:32 ` Benjamin Gray
2023-08-02 13:10 ` Michael Ellerman [this message]
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