linux-kernel - Re: [PATCH 1/3] arm: Fix flush_dcache

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Date:   Wed, 24 May 2023 22:56:41 +0200
From:   Helge Deller <deller@....de>
To:     Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Dinh Nguyen <dinguyen@...nel.org>,
        linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] arm: Fix flush_dcache_page() for usage from irq
 context

On 5/24/23 22:00, Arnd Bergmann wrote:
> On Wed, May 24, 2023, at 17:26, Helge Deller wrote:
>> Since at least kernel 6.1, flush_dcache_page() is called with IRQs
>> disabled, e.g. from aio_complete().
>>
>> But the current implementation for flush_dcache_page() on ARM
>> unintentionally re-enables IRQs, which may lead to deadlocks.
>>
>> Fix it by using xa_lock_irqsave() and xa_unlock_irqrestore()
>> for the flush_dcache_mmap_*lock() macros instead.
>>
>> Cc: Russell King (Oracle) <linux@...linux.org.uk>
>> Cc: Arnd Bergmann <arnd@...db.de>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Signed-off-by: Helge Deller <deller@....de>
>
> Cc: stable@...r.kernel.org
> Reviewed-by: Arnd Bergmann <arnd@...db.de>

Thanks!
I assume it's picked up in the arm git tree then.

>  From what I can tell, the behavior in aio_complete has been
> there for over 10 years, since 21b40200cfe96 ("aio: use
> flush_dcache_page()").

Oh, then those arches are broken since then.

> Others may have done the same already back then.
>
> I also see you sent patches for nios2 and parisc, but not
> for csky, which appears to need the same thing.

csky doesn't use flush_dcache_mmap_lock() inside it's
flush_dcache_page() function, so I think it's not affected.

Helge