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The body uses it correctly via "desc->num_sgs" and "desc->sg_req[i].len", but the cyclic check incorrectly looks at the channel's stale current descriptor instead: if (lchan->desc->cyclic && next_sg == 0) return residue; This breaks when the function is called from the vdesc fallback path of loongson2_cmc_dma_tx_status(): if (lchan->desc && cookie == lchan->desc->vdesc.tx.cookie) state->residue = ...desc_residue(lchan, lchan->desc, ...); else if (vdesc) state->residue = ...desc_residue(lchan, to_lmdma_desc(vdesc), 0); The else-if branch is taken precisely when "lchan->desc" is NULL or points to a different descriptor than the one being queried, so dereferencing "lchan->desc->cyclic" inside the helper either NULL- derefs or reads the wrong descriptor's flag. smatch flags this: drivers/dma/loongson/loongson2-apb-cmc-dma.c:516 loongson2_cmc_dma_tx_status() error: we previously assumed 'lchan->desc' could be null (see line 512) Use the "desc" parameter, matching how the rest of the function already accesses fields of the descriptor under inspection. Signed-off-by: Stepan Ionichev --- drivers/dma/loongson/loongson2-apb-cmc-dma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/dma/loongson/loongson2-apb-cmc-dma.c b/drivers/dma/loongson/loongson2-apb-cmc-dma.c index 1c9a542ed..3b02bcd75 100644 --- a/drivers/dma/loongson/loongson2-apb-cmc-dma.c +++ b/drivers/dma/loongson/loongson2-apb-cmc-dma.c @@ -487,7 +487,7 @@ static size_t loongson2_cmc_dma_desc_residue(struct loongson2_cmc_dma_chan *lcha ndtr = loongson2_cmc_dma_read(lddev, LOONGSON2_CMCDMA_CNDTR, lchan->id); residue = ndtr << width; - if (lchan->desc->cyclic && next_sg == 0) + if (desc->cyclic && next_sg == 0) return residue; for (i = next_sg; i < desc->num_sgs; i++) -- 2.43.0