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 6926A50C28B; Wed, 30 Sep 2026 18:11:51 +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=1790791912; cv=none; b=JtokWclR3FGzEBrxLGHTVUD4iduOYgoZ1l2597tOGYK6r5VObYvqrI/oYqL2mm9oUSDPE154Iux1h2RGC343ybY++0/8QDm4CPff2xgvepZZ/OgI2Z/5//M4ESp/c66dxrFWRbq0Z4yFgElFP92//TpVgzwJl4bS90A7nELg+2U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790791912; c=relaxed/simple; bh=sWkRx2mdguSwtwT1RJoD1A0fP0QfLXfDeXCVSzLqT6k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RhJHTCC8id4OPwS9m5y/MDgeeQWvuyn78DSlLnv/KQ7+XAWE5JBcRKfCIJxX6xXGYylDfOndLJL7fP9sYej5iJyPFWMgOT7bv72kXk3A0XWkPGoeBdn1sx1c/y97pXtDPlHUYZBwiWAwoRyUNynQUj1nEfpJ5/GEYZBijp4EgWw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=EXrJ6l6V; 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="EXrJ6l6V" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D7451F000FF; Wed, 30 Sep 2026 18:11:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790791911; bh=/fc79w0b0XUa/BXd529OLnaBpcyuGlYWt0eVnS5RB+A=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=EXrJ6l6VZ65sM6nfV24ezEpHKdIGFbKzougQEQJxtZLkdoFVdMz+2Wb5T1dCTueKt 9p11p6UeTD53GoO9OhmyMlgfUlpr3hfuAjgB/+9NgXQZAHDWzX6mwbTybudBQm1Jh8 oLxQ1UzGrn7C7tWt6XZq/Rh6BhcER9ji6TN7Q180= 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 5.15 470/752] dmaengine: Fix device kref underflow in dma_chan_put() Date: Wed, 30 Sep 2026 17:25:40 +0200 Message-ID: <20260930152408.443825950@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152358.131179731@linuxfoundation.org> References: <20260930152358.131179731@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 5.15-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 68078e83d5756..7eb3ec8323ccc 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