dmaengine: Fix device kref underflow in dma_chan_put()

Browse source

dma_chan_get() takes chan->device->ref only on the slow path:

	/* no kref on fast path */
	if (chan->client_count) {
		__module_get(owner);
		chan->client_count++;
		return 0;
	}
	if (!try_module_get(owner))
		return -ENODEV;
	if (!dma_device_get(chan->device)) { // calls kref_get_unless_zero()

dma_chan_put() drops the ref unconditionally, so every fast-path
get/put pair drops one extra device reference.

The bug fires when two conditions hold together: a non-private
provider has a persistent client holding chan->client_count > 0
and another client cycles dmaengine_get()/dmaengine_put().
When the kref hits zero, the subsequent dma_find_channel() returns
NULL even though the provider module is still loaded.

Fix this by dropping device->ref only on the last put, matching the
single slow-path get.

Fixes: 8ad342a863 ("dmaengine: Add reference counting to dma_device struct")
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
Link: https://patch.msgid.link/20260822-dmaengine-kref-fix-v5-2-d4a4ee47d927@amd.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

...

This commit is contained in:

Shivank Garg 2026-08-22 19:22:04 +00:00 • committed by Vinod Koul

parent 424103642d

commit 44dab65906

1 changed files with 3 additions and 1 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

4

drivers/dma/dmaengine.c

View file