patch "iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf()" added to char-misc-linus

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf()

to my char-misc git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-linus branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.

If you have any questions about this process, please let me know.


From a093999355084bdbfe6e97f1dd232e58a1525f0b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20Monin?= <benoit.monin@bootlin.com>
Date: Wed, 1 Apr 2026 17:24:58 +0200
Subject: iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf()
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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 <jamesnuss@nanometrics.ca>
Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
---
 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();
-- 
2.54.0