linux-kernel - Re: [PATCH] xarray: Add a BUG_ON() to ensure caller is not sibling

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Message-ID: <4fb15ee4-1049-4459-a10e-9f4544545a20@arm.com>
Date: Thu, 29 May 2025 08:47:53 +0530
From: Dev Jain <dev.jain@....com>
To: Zi Yan <ziy@...dia.com>
Cc: akpm@...ux-foundation.org, willy@...radead.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, david@...hat.com, anshuman.khandual@....com,
 ryan.roberts@....com
Subject: Re: [PATCH] xarray: Add a BUG_ON() to ensure caller is not sibling


On 28/05/25 10:42 pm, Zi Yan wrote:
> On 28 May 2025, at 7:31, Dev Jain wrote:
>
>> Suppose xas is pointing somewhere near the end of the multi-entry batch.
>> Then it may happen that the computed slot already falls beyond the batch,
>> thus breaking the loop due to !xa_is_sibling(), and computing the wrong
>> order. Thus ensure that the caller is aware of this by triggering a BUG
>> when the entry is a sibling entry.
> Is it possible to add a test case in lib/test_xarray.c for this?
> You can compile the tests with “make -C tools/testing/radix-tree”
> and run “./tools/testing/radix-tree/xarray”.


Sorry forgot to Cc you.
I can surely do that later, but does this patch look fine?


>
>> This patch is motivated by code inspection and not a real bug report.
>>
>> Signed-off-by: Dev Jain <dev.jain@....com>
>> ---
>> The patch applies on 6.15 kernel.
>>
>>   lib/xarray.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/lib/xarray.c b/lib/xarray.c
>> index 9644b18af18d..0f699766c24f 100644
>> --- a/lib/xarray.c
>> +++ b/lib/xarray.c
>> @@ -1917,6 +1917,8 @@ int xas_get_order(struct xa_state *xas)
>>   	if (!xas->xa_node)
>>   		return 0;
>>
>> +	XA_NODE_BUG_ON(xas->xa_node, xa_is_sibling(xa_entry(xas->xa,
>> +		       xas->xa_node, xas->xa_offset)));
>>   	for (;;) {
>>   		unsigned int slot = xas->xa_offset + (1 << order);
>>
>> -- 
>> 2.30.2
>
> Best Regards,
> Yan, Zi