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io_uring: only post the dummy skip CQE on CQE_MIXED rings

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io_cqe_cache_refill() posts a dummy skip CQE when a 32b CQE would
straddle the end of the ring, so the real one can start at offset 0. That
only makes sense on CQE_MIXED rings, where slots are 16b and a 32b CQE
needs two of them back to back. On a CQE32 ring every slot is already
32b, but io_fill_cqe_aux32() still passes cqe32 == true, and the dummy
then gets written at cqes[off] rather than cqes[off << 1], inside another
CQE.

Limit the dummy to CQE_MIXED rings.

Fixes: e26dca67fd ("io_uring: add support for IORING_SETUP_CQE_MIXED")
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
Link: https://patch.msgid.link/20260919203516.2581409-1-benquike@gmail.com
[axboe: split from Hui's original patch, edited commit message]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Hui Peng 2026-09-19 20:35:16 +00:00 committed by Jens Axboe
parent 50b617ba78
commit 2107751744
1 changed files with 2 additions and 1 deletions
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3
io_uring/io_uring.c
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@ -733,7 +733,8 @@ bool io_cqe_cache_refill(struct io_ring_ctx *ctx, bool overflow, bool cqe32)
* Post dummy CQE if a 32b CQE is needed and there's only room for a
* 16b CQE before the ring wraps.
*/
if (cqe32 && off + 1 == ctx->cq_entries) {
if (cqe32 && (ctx->flags & IORING_SETUP_CQE_MIXED) &&
off + 1 == ctx->cq_entries) {
if (!io_fill_nop_cqe(ctx, off))
return false;
off = 0;