From 2d0e88f3fd1dcb37072d499c36162baf5b009d41 Mon Sep 17 00:00:00 2001 From: Caleb Sander Mateos Date: Tue, 11 Nov 2025 12:15:29 -0700 Subject: [PATCH] io_uring/rsrc: don't use blk_rq_nr_phys_segments() as number of bvecs io_buffer_register_bvec() currently uses blk_rq_nr_phys_segments() as the number of bvecs in the request. However, bvecs may be split into multiple segments depending on the queue limits. Thus, the number of segments may overestimate the number of bvecs. For ublk devices, the only current users of io_buffer_register_bvec(), virt_boundary_mask, seg_boundary_mask, max_segments, and max_segment_size can all be set arbitrarily by the ublk server process. Set imu->nr_bvecs based on the number of bvecs the rq_for_each_bvec() loop actually yields. However, continue using blk_rq_nr_phys_segments() as an upper bound on the number of bvecs when allocating imu to avoid needing to iterate the bvecs a second time. Link: https://lore.kernel.org/io-uring/20251111191530.1268875-1-csander@purestorage.com/ Signed-off-by: Caleb Sander Mateos Fixes: 27cb27b6d5ea ("io_uring: add support for kernel registered bvecs") Reviewed-by: Ming Lei Reviewed-by: Chaitanya Kulkarni Signed-off-by: Jens Axboe --- io_uring/rsrc.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c index 2602d76d5ff0..0010c4992490 100644 --- a/io_uring/rsrc.c +++ b/io_uring/rsrc.c @@ -943,8 +943,8 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq, struct req_iterator rq_iter; struct io_mapped_ubuf *imu; struct io_rsrc_node *node; - struct bio_vec bv, *bvec; - u16 nr_bvecs; + struct bio_vec bv; + unsigned int nr_bvecs = 0; int ret = 0; io_ring_submit_lock(ctx, issue_flags); @@ -965,8 +965,11 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq, goto unlock; } - nr_bvecs = blk_rq_nr_phys_segments(rq); - imu = io_alloc_imu(ctx, nr_bvecs); + /* + * blk_rq_nr_phys_segments() may overestimate the number of bvecs + * but avoids needing to iterate over the bvecs + */ + imu = io_alloc_imu(ctx, blk_rq_nr_phys_segments(rq)); if (!imu) { kfree(node); ret = -ENOMEM; @@ -977,16 +980,15 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq, imu->len = blk_rq_bytes(rq); imu->acct_pages = 0; imu->folio_shift = PAGE_SHIFT; - imu->nr_bvecs = nr_bvecs; refcount_set(&imu->refs, 1); imu->release = release; imu->priv = rq; imu->is_kbuf = true; imu->dir = 1 << rq_data_dir(rq); - bvec = imu->bvec; rq_for_each_bvec(bv, rq, rq_iter) - *bvec++ = bv; + imu->bvec[nr_bvecs++] = bv; + imu->nr_bvecs = nr_bvecs; node->buf = imu; data->nodes[index] = node; -- 2.47.3