tjh.dev / kernel
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padata: use integer wrap around to prevent deadlock on seq_nr overflow

When submitting more than 2^32 padata objects to padata_do_serial, the
current sorting implementation incorrectly sorts padata objects with
overflowed seq_nr, causing them to be placed before existing objects in
the reorder list. This leads to a deadlock in the serialization process
as padata_find_next cannot match padata->seq_nr and pd->processed
because the padata instance with overflowed seq_nr will be selected
next.

To fix this, we use an unsigned integer wrap around to correctly sort
padata objects in scenarios with integer overflow.

Fixes: bfde23ce200e ("padata: unbind parallel jobs from specific CPUs")
Cc: <stable@vger.kernel.org>
Co-developed-by: Christian Gafert <christian.gafert@rohde-schwarz.com>
Signed-off-by: Christian Gafert <christian.gafert@rohde-schwarz.com>
Co-developed-by: Max Ferger <max.ferger@rohde-schwarz.com>
Signed-off-by: Max Ferger <max.ferger@rohde-schwarz.com>
Signed-off-by: Van Giang Nguyen <vangiang.nguyen@rohde-schwarz.com>
Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

authored by

VanGiang Nguyen and committed by
Herbert Xu 9a22b281 f2f853e7

+2 -1
+2 -1
kernel/padata.c
··· 404 404 /* Sort in ascending order of sequence number. */ 405 405 list_for_each_prev(pos, &reorder->list) { 406 406 cur = list_entry(pos, struct padata_priv, list); 407 - if (cur->seq_nr < padata->seq_nr) 407 + /* Compare by difference to consider integer wrap around */ 408 + if ((signed int)(cur->seq_nr - padata->seq_nr) < 0) 408 409 break; 409 410 } 410 411 list_add(&padata->list, pos);