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Subject: Re: [PATCH v1 2/4] powerpc/mm: print warning in
 arch_remove_linear_mapping()
To:     osalvador <osalvador@suse.de>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linuxppc-dev@lists.ozlabs.org,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Rashmica Gupta <rashmica.g@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@kernel.org>,
        Michal Hocko <mhocko@suse.com>,
        Wei Yang <richard.weiyang@linux.alibaba.com>
References: <20201029162718.29910-1-david@redhat.com>
 <20201029162718.29910-3-david@redhat.com>
 <20201104094255.GA4981@localhost.localdomain>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <78f48ca7-d801-238d-f107-11b82d8a6384@redhat.com>
Date:   Wed, 11 Nov 2020 13:10:15 +0100
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On 04.11.20 10:42, osalvador wrote:
> On Thu, Oct 29, 2020 at 05:27:16PM +0100, David Hildenbrand wrote:
>> Let's print a warning similar to in arch_add_linear_mapping() instead of
>> WARN_ON_ONCE() and eventually crashing the kernel.
>>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> Cc: Paul Mackerras <paulus@samba.org>
>> Cc: Rashmica Gupta <rashmica.g@gmail.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Mike Rapoport <rppt@kernel.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>   arch/powerpc/mm/mem.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
>> index 8a86d81f8df0..685028451dd2 100644
>> --- a/arch/powerpc/mm/mem.c
>> +++ b/arch/powerpc/mm/mem.c
>> @@ -145,7 +145,9 @@ void __ref arch_remove_linear_mapping(u64 start, u64 size)
>>   	flush_dcache_range_chunked(start, start + size, FLUSH_CHUNK_SIZE);
>>   
>>   	ret = remove_section_mapping(start, start + size);
>> -	WARN_ON_ONCE(ret);
>> +	if (ret)
>> +		pr_warn("Unable to remove linear mapping for 0x%llx..0x%llx: %d\n",
>> +			start, start + size, ret);
> 
> I guess the fear is to panic on systems that do have panic_on_warn (not
> sure how many productions systems have this out there).

Exactly.

> But anyway, being coherent with that, I think you should remove the WARN_ON
> in hash__remove_section_mapping as well.

Thanks, I'll add a patch doing that.

> 
> Besides that:
> 
> Reviewed-by: Oscar Salvador <osalvador@suse.
> 
> Not sure if the functions below that also have any sort of WARN_ON.
> native_hpte_removebolted has a VM_WARN_ON, but that is on
> CONFIG_DEBUG_VM so does not really matter.

Right. Thanks!

-- 
Thanks,

David / dhildenb