From a093999355084bdbfe6e97f1dd232e58a1525f0b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Beno=C3=AEt=20Monin?= Date: Wed, 1 Apr 2026 17:24:58 +0200 Subject: [PATCH] iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit iio_buffer_enqueue_dmabuf() allocates a struct iio_dma_fence (104 bytes, kmalloc-128) via kmalloc_obj()+dma_fence_init(), which sets the initial kref to 1. It then calls dma_resv_add_fence() which takes a second reference (kref=2), and stores a raw pointer in block->fence. On the success path the function returns without calling dma_fence_put() to release the initial reference, so every buffer enqueue permanently leaks one kmalloc-128 allocation. The iio_buffer_cleanup() work item only releases the temporary reference taken during completion signalling by iio_buffer_signal_dmabuf_done(); the initial reference from dma_fence_init() is never released. With four iio_rwdev instances at 240kHz and 512 samples per buffer, this produces ~1875 kmalloc-128 allocations per second matching the observed slab growth exactly. A test with ftrace confirmed that the dma_fence_destroy event was never triggered. Fix by calling dma_fence_put() after dma_resv_add_fence(), transferring ownership of the fence to the DMA reservation object. The DMA fence then gets properly discarded after being signalled. Fixes: 3e26d9f08fbe0 ("iio: core: Add new DMABUF interface infrastructure") Originally-by: James Nuss Signed-off-by: Benoît Monin Reviewed-by: Paul Cercueil Cc: Signed-off-by: Jonathan Cameron --- drivers/iio/industrialio-buffer.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c index 46f36a6ed271..5c3df993bea2 100644 --- a/drivers/iio/industrialio-buffer.c +++ b/drivers/iio/industrialio-buffer.c @@ -1909,6 +1909,7 @@ static int iio_buffer_enqueue_dmabuf(struct iio_dev_buffer_pair *ib, dma_resv_add_fence(dmabuf->resv, &fence->base, dma_to_ram ? DMA_RESV_USAGE_WRITE : DMA_RESV_USAGE_READ); + dma_fence_put(&fence->base); dma_resv_unlock(dmabuf->resv); cookie = dma_fence_begin_signalling();