From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4F0D137A825; Wed, 30 Sep 2026 19:19:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790795985; cv=none; b=LJvZSTANaErjcqFBM68UCN0mMvSuCIBMTN0SNG6xVzRD4o92Ikfe3j6m27GN8sQrBSVmPISTasGNRhrV3TcUrpJiCxmCV0OEidc/BCnfSOS3zI22g9Xw2PXoKM4Ghjjo7kinttXompYKDM490qAxnAnIEHFzMZwQgSxLGZDTKIQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790795985; c=relaxed/simple; bh=EI+rSQ3BCicZ9lVahciKvKWmYUMlliGMOXKAf2uJ5BE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mzwKTz4C96RO6sJ4XYSJoQ8qrz2x7xS0ETl3DHjZ0jkXdlnHwBs0rYe+2AuptyvDFkDoIbecbuLPHLaEQDWxBbo9bhj5V/puolt9Jlme2zpVrY4htjsCNUVD+d2Y+DIVwu8P66ukZF0H6gz+HWl2u9LnF1oNCvdVy1lZv1q1qqs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ZuUUEw1D; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ZuUUEw1D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AAB691F000FF; Wed, 30 Sep 2026 19:19:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790795984; bh=R2+F/WeRQeVpkOOeyHSR7xUaULGNqWz6MR+zVN0ep6c=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ZuUUEw1DWxjaq6UxgXCbLJH0SiCj8G7xCUUic72ZH7mgMEOJI8zYgtlIiunNcxuae Oan3dknNelyCTTIJBhWjjv2WDUFz6ZOXfFDDbNse/e1WyP3QGe4nmbiN7PwpWCByM0 eqAzObTEuKiTTxoAEBjpcSSxFCiOpJK71z3g/Xb0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Frank Li , Logan Gunthorpe , Shivank Garg , Vinod Koul , Sasha Levin Subject: [PATCH 6.6 0751/1193] dmaengine: Fix device kref underflow in dma_chan_put() Date: Wed, 30 Sep 2026 17:23:55 +0200 Message-ID: <20260930152450.937153159@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152434.301151190@linuxfoundation.org> References: <20260930152434.301151190@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Shivank Garg [ Upstream commit 44dab659064eb5c10adb0306510eebe848ed592d ] 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: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct") Reviewed-by: Frank Li Reviewed-by: Logan Gunthorpe Signed-off-by: Shivank Garg Link: https://patch.msgid.link/20260822-dmaengine-kref-fix-v5-2-d4a4ee47d927@amd.com Signed-off-by: Vinod Koul Signed-off-by: Sasha Levin --- drivers/dma/dmaengine.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index b1c9187602d53..daaab1078d050 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -513,7 +513,9 @@ static void dma_chan_put(struct dma_chan *chan) chan->route_data = NULL; } - dma_device_put(chan->device); + /* This channel is not in use anymore, drop the device ref */ + if (!chan->client_count) + dma_device_put(chan->device); module_put(dma_chan_to_owner(chan)); } -- 2.53.0