linux-kernel - Re: [PATCH 2/3] nios2: Fix flush_dcache

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Date:   Mon, 19 Jun 2023 12:10:26 +0200
From:   Helge Deller <deller@....de>
To:     Dinh Nguyen <dinguyen@...nel.org>, linux@...linux.org.uk,
        linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org
Subject: Re: [PATCH 2/3] nios2: Fix flush_dcache_page() for usage from irq
 context

Hi Dinh,

On 6/14/23 00:39, Dinh Nguyen wrote:
> Thanks for the patch. Does it need a Fixes tag?

I did not add a fixes tag for the parisc or arm version.

The code was originally correct, but later patches then suddenly started
using cache flushes from irq context (e.g. 21b40200cfe96 ("aio: use
flush_dcache_page()")) which then triggers the bug.
So, it's hard to say that it fixes one specific commit.

I suggest you backport it as far as possible.

Helge

> Dinh
>
> On 5/24/23 10:26, 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 NIOS2
>> 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: Dinh Nguyen <dinguyen@...nel.org>
>> Signed-off-by: Helge Deller <deller@....de>
>> ---
>>   arch/nios2/include/asm/cacheflush.h | 4 ++++
>>   arch/nios2/mm/cacheflush.c          | 5 +++--
>>   2 files changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/nios2/include/asm/cacheflush.h b/arch/nios2/include/asm/cacheflush.h
>> index d0b71dd71287..a37242662809 100644
>> --- a/arch/nios2/include/asm/cacheflush.h
>> +++ b/arch/nios2/include/asm/cacheflush.h
>> @@ -48,5 +48,9 @@ extern void invalidate_dcache_range(unsigned long start, unsigned long end);
>>
>>   #define flush_dcache_mmap_lock(mapping)        xa_lock_irq(&mapping->i_pages)
>>   #define flush_dcache_mmap_unlock(mapping)    xa_unlock_irq(&mapping->i_pages)
>> +#define flush_dcache_mmap_lock_irqsave(mapping, flags)        \
>> +        xa_lock_irqsave(&mapping->i_pages, flags)
>> +#define flush_dcache_mmap_unlock_irqrestore(mapping, flags)    \
>> +        xa_unlock_irqrestore(&mapping->i_pages, flags)
>>
>>   #endif /* _ASM_NIOS2_CACHEFLUSH_H */
>> diff --git a/arch/nios2/mm/cacheflush.c b/arch/nios2/mm/cacheflush.c
>> index 6aa9257c3ede..35f3b599187f 100644
>> --- a/arch/nios2/mm/cacheflush.c
>> +++ b/arch/nios2/mm/cacheflush.c
>> @@ -75,11 +75,12 @@ static void flush_aliases(struct address_space *mapping, struct page *page)
>>   {
>>       struct mm_struct *mm = current->active_mm;
>>       struct vm_area_struct *mpnt;
>> +    unsigned long flags;
>>       pgoff_t pgoff;
>>
>>       pgoff = page->index;
>>
>> -    flush_dcache_mmap_lock(mapping);
>> +    flush_dcache_mmap_lock_irqsave(mapping, flags);
>>       vma_interval_tree_foreach(mpnt, &mapping->i_mmap, pgoff, pgoff) {
>>           unsigned long offset;
>>
>> @@ -92,7 +93,7 @@ static void flush_aliases(struct address_space *mapping, struct page *page)
>>           flush_cache_page(mpnt, mpnt->vm_start + offset,
>>               page_to_pfn(page));
>>       }
>> -    flush_dcache_mmap_unlock(mapping);
>> +    flush_dcache_mmap_unlock_irqrestore(mapping, flags);
>>   }
>>
>>   void flush_cache_all(void)
>> --
>> 2.38.1
>>