* Re: Hit an assertion within lib/xarray.c from lib/test_xarray.c, would like help debugging
2025-10-28 22:34 Hit an assertion within lib/xarray.c from lib/test_xarray.c, would like help debugging Ackerley Tng
@ 2025-10-31 10:40 ` David Hildenbrand
2025-11-15 6:58 ` Dev Jain
1 sibling, 0 replies; 3+ messages in thread
From: David Hildenbrand @ 2025-10-31 10:40 UTC (permalink / raw)
To: Ackerley Tng, willy, akpm, linux-fsdevel, linux-mm, linux-kernel
Cc: michael.roth, vannapurve
On 28.10.25 23:34, Ackerley Tng wrote:
> Hi!
>
Hi!
> I'm trying to use multi-index xarrays and I was experimenting with
> test_xarray.c.
>
> I'm trying to use xa_erase() on every index after splitting the entry in the
> xarray. (and I commented out every other test case just to focus on this test)
>
> Should erasing every index within the xarray after splitting be a supported use
> case?
>
> Here's the diff:
>
> diff --git i/lib/test_xarray.c w/lib/test_xarray.c
> index 5ca0aefee9aa5..fe74f44bbbd92 100644
> --- i/lib/test_xarray.c
> +++ w/lib/test_xarray.c
> @@ -1868,6 +1868,9 @@ static void check_split_1(struct xarray *xa, unsigned long index,
> rcu_read_unlock();
> XA_BUG_ON(xa, found != 1 << (order - new_order));
>
> + for (i = 0; i < (1 << order); i++)
> + xa_erase(xa, index + i);
> +
> xa_destroy(xa);
> }
>
> And made a call to
>
> check_split_1(xa, 0, 3, 2);
>
> Here's the assertion I hit:
>
> node 0x7c4de89e01c0x offset 0 parent 0x7c4de89e0100x shift 0 count 4 values 254 array 0x55edd2dd8940x list 0x7c4de89e01d8x 0x7c4de89e01d8x marks 0 10 0
> xarray: ../shared/../../../lib/xarray.c:764: update_node: Assertion `!(1)' failed.
>
>
> I think I've narrowed down the issue to the for (;;) loop in xas_store(), which
> I believe isn't counting the `values` to be updated in update_node() correctly.
I wish i could help, but I'm not an expert on that code and it's not the
easiest code to read :) But staring at it a bit I assume you are right
on that one.
>
> Is `values += !xa_is_value(first) - !value;` intended to compute the increase in
> number of values with replacement of every slot being iterated by the new entry?
Unfortunately that I am also not 100% sure about that one.
--
Cheers
David / dhildenb
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Hit an assertion within lib/xarray.c from lib/test_xarray.c, would like help debugging
2025-10-28 22:34 Hit an assertion within lib/xarray.c from lib/test_xarray.c, would like help debugging Ackerley Tng
2025-10-31 10:40 ` David Hildenbrand
@ 2025-11-15 6:58 ` Dev Jain
1 sibling, 0 replies; 3+ messages in thread
From: Dev Jain @ 2025-11-15 6:58 UTC (permalink / raw)
To: Ackerley Tng, willy, akpm, linux-fsdevel, linux-mm, linux-kernel
Cc: david, michael.roth, vannapurve
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On 29/10/25 4:04 am, Ackerley Tng wrote:
> Hi!
>
> I'm trying to use multi-index xarrays and I was experimenting with
> test_xarray.c.
>
> I'm trying to use xa_erase() on every index after splitting the entry in the
> xarray. (and I commented out every other test case just to focus on this test)
>
> Should erasing every index within the xarray after splitting be a supported use
> case?
>
> Here's the diff:
>
> diff --git i/lib/test_xarray.c w/lib/test_xarray.c
> index 5ca0aefee9aa5..fe74f44bbbd92 100644
> --- i/lib/test_xarray.c
> +++ w/lib/test_xarray.c
> @@ -1868,6 +1868,9 @@ static void check_split_1(struct xarray *xa, unsigned long index,
> rcu_read_unlock();
> XA_BUG_ON(xa, found != 1 << (order - new_order));
>
> + for (i = 0; i < (1 << order); i++)
> + xa_erase(xa, index + i);
> +
> xa_destroy(xa);
> }
>
> And made a call to
>
> check_split_1(xa, 0, 3, 2);
>
> Here's the assertion I hit:
>
> node 0x7c4de89e01c0x offset 0 parent 0x7c4de89e0100x shift 0 count 4 values 254 array 0x55edd2dd8940x list 0x7c4de89e01d8x 0x7c4de89e01d8x marks 0 10 0
> xarray: ../shared/../../../lib/xarray.c:764: update_node: Assertion `!(1)' failed.
I changed that function to the following:
staticvoidcheck_split_1(structxarray *xa, unsignedlongindex,
unsignedintorder, unsignedintnew_order)
{
XA_STATE_ORDER(xas, xa, index, new_order);
unsignedinti;
for(i = 0; i < (1<< order); i += (1<< new_order))
xa_store_order(xa, i, new_order, xa, GFP_KERNEL);
xas_lock(&xas);
for(i = 0; i < (1<< order); i += (1<< new_order))
__xa_store(xa, index + i, xa_mk_index(index + i), 0);
xas_unlock(&xas);
xa_erase(xa, index);
xa_destroy(xa);
} and I still hit the assertion. I think the new function is still a valid code sequence -
Store multi-indices of new_order, for length = 1 << order. Then, replace those entries
with xa_mk_index(index + i). Then erase the first index.
>
>
> I think I've narrowed down the issue to the for (;;) loop in xas_store(), which
> I believe isn't counting the `values` to be updated in update_node() correctly.
>
> Is `values += !xa_is_value(first) - !value;` intended to compute the increase in
> number of values with replacement of every slot being iterated by the new entry?
>
> Why does the computation of `count` involve next and entry, and why does the
> computation for `values` only statically depend on the initial value of entry,
> and on first instead of next?
Yeah there is some issue here only - but the code seems to work, tried a lot of
different combinations in my head like throwing out a non-value and putting in
a value, then vice-versa, then putting a NULL entry - can't figure out the problem :(
>
> Thanks,
>
>
> Ackerley
>
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