Messages in this thread Patch in this message |  | | From | Bjorn Andersson <> | | Date | Tue, 31 Mar 2026 22:22:49 -0500 | | Subject | [PATCH v2 7/7] slimbus: qcom-ngd-ctrl: Avoid ABBA on tx_lock/ctrl->lock |
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During the SSR/PDR down notification the tx_lock is taken with the intent to provide synchronization with active DMA transfers.
But during this period qcom_slim_ngd_down() is invoked, which ends up in slim_report_absent(), which takes the slim_controller lock. In multiple other codepaths these two locks are taken in the opposite order (i.e. slim_controller then tx_lock).
The result is a lockdep splat, and a possible deadlock:
rprocctl/449 is trying to acquire lock: ffff00009793e620 (&ctrl->lock){+.+.}-{4:4}, at: slim_report_absent (drivers/slimbus/core.c:322) slimbus
but task is already holding lock: ffff00009793fb50 (&ctrl->tx_lock){+.+.}-{4:4}, at: qcom_slim_ngd_ssr_pdr_notify (drivers/slimbus/qcom-ngd-ctrl.c:1475) slim_qcom_ngd_ctrl
which lock already depends on the new lock.
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&ctrl->tx_lock); lock(&ctrl->lock); lock(&ctrl->tx_lock); lock(&ctrl->lock);
The assumption is that the comment refers to the desire to not call qcom_slim_ngd_exit_dma() while we have an ongoing DMA TX transaction. But any such transaction is initiated and completed within a single qcom_slim_ngd_xfer_msg().
Prior to calling qcom_slim_ngd_exit_dma() the slim_controller is torn down, all child devices are notified that the slimbus is gone and the child devices are removed.
Stop taking the tx_lock in qcom_slim_ngd_ssr_pdr_notify() to avoid the deadlock.
Fixes: a899d324863a ("slimbus: qcom-ngd-ctrl: add Sub System Restart support") Cc: stable@vger.kernel.org Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com> --- drivers/slimbus/qcom-ngd-ctrl.c | 3 --- 1 file changed, 3 deletions(-)
diff --git a/drivers/slimbus/qcom-ngd-ctrl.c b/drivers/slimbus/qcom-ngd-ctrl.c index afd2171d3be2c4c19994e9ebedc63dedfba899e0..2ff4374a1e0ce5d3d8f9b074f19fe77daeb79dae 100644 --- a/drivers/slimbus/qcom-ngd-ctrl.c +++ b/drivers/slimbus/qcom-ngd-ctrl.c @@ -1471,15 +1471,12 @@ static int qcom_slim_ngd_ssr_pdr_notify(struct qcom_slim_ngd_ctrl *ctrl, switch (action) { case QCOM_SSR_BEFORE_SHUTDOWN: case SERVREG_SERVICE_STATE_DOWN: - /* Make sure the last dma xfer is finished */ - mutex_lock(&ctrl->tx_lock); if (ctrl->state != QCOM_SLIM_NGD_CTRL_DOWN) { pm_runtime_get_noresume(ctrl->ctrl.dev); ctrl->state = QCOM_SLIM_NGD_CTRL_DOWN; qcom_slim_ngd_down(ctrl); qcom_slim_ngd_exit_dma(ctrl); } - mutex_unlock(&ctrl->tx_lock); break; case QCOM_SSR_AFTER_POWERUP: case SERVREG_SERVICE_STATE_UP: -- 2.51.0
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