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 C7CAD25F7A9; Wed, 30 Sep 2026 16:29:21 +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=1790785762; cv=none; b=hpBByM/DTH9WAysMxwGXetg3UFsyR3CUWzZWHYCZcYAvzY56nqsyzIpBRkhoi/VtHakU3d+sxA9MULhTa/vrTjmAhHUMX0ZyT9VVj8ZzIiUI33x9sG20F7YuV31M44+32ke1EwdMXuVfB5vSErGkvpafMcCnWvAu6Qm34WqFXAI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790785762; c=relaxed/simple; bh=SI4/7w4lp2yIUsYufSJw9Xe104tnX9n3U2zeLqN35uw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=iZzAp6uQy8ohmz+6YeW1qWhbo1Mb8WNBc5PQF3CdSUcoexd8h3JmrXvkRFbplaLZsveLFWapw8oRP6coabrr9YVU/or70UZTd9+3qne4/FLYP8pmrG0cweJkCSncVCxaaiwM7/kavspaMOmqWF+7HNr6Fmodjfez/jlPinsX7nY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=kNH8x9Lv; 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="kNH8x9Lv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2ADCF1F00893; Wed, 30 Sep 2026 16:29:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790785761; bh=HMjGaCy7ULgtqrRsFazwnJsCgF4H5vsVfS2nS5++j/A=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=kNH8x9Lv7u3AiEIGekiLe+N6sMqCAEeNB8QUSAnCJ9QiyjrakOw21u4saSVq2Gza3 qsce66+DABk0leJksPQcVY39et7kGTY4mBRXJSoieq3EojljjoXA9UpeWxjtLpIR7g 8FLvi3O+gP3WkEK09z0RBrQJolCWmg/D1IeEV02Y= 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 6.1 622/982] dmaengine: Fix device kref underflow in dma_chan_put() Date: Wed, 30 Sep 2026 17:22:38 +0200 Message-ID: <20260930152430.134747674@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152416.775402466@linuxfoundation.org> References: <20260930152416.775402466@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 6.1-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 d89827d0927e4..294a00ea56990 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