linux-kernel - Re: [PATCH v3] mm: fix unexpected changes to {failslab|fail_page

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Date:   Sat, 19 Nov 2022 08:48:36 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     akinobu.mita@...il.com, dvyukov@...gle.com, jgg@...dia.com,
        willy@...radead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] mm: fix unexpected changes to
 {failslab|fail_page_alloc}.attr



On 2022/11/19 05:42, Andrew Morton wrote:
> On Fri, 18 Nov 2022 18:00:11 +0800 Qi Zheng <zhengqi.arch@...edance.com> wrote:
> 
>> When we specify __GFP_NOWARN, we only expect that no warnings
>> will be issued for current caller. But in the __should_failslab()
>> and __should_fail_alloc_page(), the local GFP flags alter the
>> global {failslab|fail_page_alloc}.attr, which is persistent and
>> shared by all tasks. This is not what we expected, let's fix it.
>>
>> Cc: stable@...r.kernel.org
>> Fixes: 3f913fc5f974 ("mm: fix missing handler for __GFP_NOWARN")
>> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>> Reviewed-by: Akinobu Mita <akinobu.mita@...il.com>
>>
>> ...
>>
>> -bool should_fail(struct fault_attr *attr, ssize_t size)
>> +bool should_fail_ex(struct fault_attr *attr, ssize_t size, int flags)
>>   {
>>   	bool stack_checked = false;
>>   
>> @@ -152,13 +149,20 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
>>   		return false;
>>   
>>   fail:
>> -	fail_dump(attr);
>> +	if (!(flags & FAULT_NOWARN))
>> +		fail_dump(attr);
>>   
>>   	if (atomic_read(&attr->times) != -1)
>>   		atomic_dec_not_zero(&attr->times);
>>   
>>   	return true;
>>   }
>> +EXPORT_SYMBOL_GPL(should_fail_ex);
> 
> I don't see a need to export this?

Yes, my initial thought was that there might be a driver using this
function, but there really isn't one yet.

And I see you've helped remove this, thanks a lot. :)

> 
> 

-- 
Thanks,
Qi