Re: [PATCH 2/3] usb: typec: ucsi: Move unregister out of atomic section

Dmitry Baryshkov
2024-08-19T01:16:32Z

On 19 August 2024 06:17:38 GMT+07:00, Bjorn Andersson <quic_bjorande@quicinc.com> wrote:
>Commit 'caa855189104 ("soc: qcom: pmic_glink: Fix race during
>initialization")' moved the pmic_glink client list under a spinlock, as
>it is accessed by the rpmsg/glink callback, which in turn is invoked
>from IRQ context.
>
>This means that ucsi_unregister() is now called from IRQ context, which
>isn't feasible as it's expecting a sleepable context. An effort is under
>way to get GLINK to invoke its callbacks in a sleepable context, but
>until then lets schedule the unregistration.
>
>A side effect of this is that ucsi_unregister() can now happen
>after the remote processor, and thereby the communication link with it, is
>gone. pmic_glink_send() is amended with a check to avoid the resulting
>NULL pointer dereference, but it becomes expecting to see a failing send
>upon shutting down the remote processor (e.g. during a restart following
>a firmware crash):
>
> ucsi_glink.pmic_glink_ucsi pmic_glink.ucsi.0: failed to send UCSI write request: -5
>
>Fixes: caa855189104 ("soc: qcom: pmic_glink: Fix race during initialization")
>Cc: stable@vger.kernel.org
>Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
>---
> drivers/soc/qcom/pmic_glink.c | 10 +++++++++-
> drivers/usb/typec/ucsi/ucsi_glink.c | 28 +++++++++++++++++++++++-----
> 2 files changed, 32 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/soc/qcom/pmic_glink.c b/drivers/soc/qcom/pmic_glink.c
>index 58ec91767d79..e4747f1d3da5 100644
>--- a/drivers/soc/qcom/pmic_glink.c
>+++ b/drivers/soc/qcom/pmic_glink.c
>@@ -112,8 +112,16 @@ EXPORT_SYMBOL_GPL(pmic_glink_register_client);
> int pmic_glink_send(struct pmic_glink_client *client, void *data, size_t len)
> {
> struct pmic_glink *pg = client->pg;
>+ int ret;
>
>- return rpmsg_send(pg->ept, data, len);
>+ mutex_lock(&pg->state_lock);
>+ if (!pg->ept)
>+ ret = -ECONNRESET;
>+ else
>+ ret = rpmsg_send(pg->ept, data, len);
>+ mutex_unlock(&pg->state_lock);
>+
>+ return ret;
> }
> EXPORT_SYMBOL_GPL(pmic_glink_send);
>
>diff --git a/drivers/usb/typec/ucsi/ucsi_glink.c b/drivers/usb/typec/ucsi/ucsi_glink.c
>index ac53a81c2a81..a33056eec83d 100644
>--- a/drivers/usb/typec/ucsi/ucsi_glink.c
>+++ b/drivers/usb/typec/ucsi/ucsi_glink.c
>@@ -68,6 +68,9 @@ struct pmic_glink_ucsi {
>
> struct work_struct notify_work;
> struct work_struct register_work;
>+ spinlock_t state_lock;
>+ unsigned int pdr_state;
>+ unsigned int new_pdr_state;
>
> u8 read_buf[UCSI_BUF_SIZE];
> };
>@@ -244,8 +247,22 @@ static void pmic_glink_ucsi_notify(struct work_struct *work)
> static void pmic_glink_ucsi_register(struct work_struct *work)
> {
> struct pmic_glink_ucsi *ucsi = container_of(work, struct pmic_glink_ucsi, register_work);
>+ unsigned long flags;
>+ unsigned int new_state;
>+
>+ spin_lock_irqsave(&ucsi->state_lock, flags);
>+ new_state = ucsi->new_pdr_state;
>+ spin_unlock_irqrestore(&ucsi->state_lock, flags);
>+
>+ if (ucsi->pdr_state != SERVREG_SERVICE_STATE_UP) {
>+ if (new_state == SERVREG_SERVICE_STATE_UP)
>+ ucsi_register(ucsi->ucsi);
>+ } else {
>+ if (new_state == SERVREG_SERVICE_STATE_DOWN)
>+ ucsi_unregister(ucsi->ucsi);
>+ }
>
>- ucsi_register(ucsi->ucsi);
>+ ucsi->pdr_state = new_state;
> }

Is there a chance if a race condition if the firmware is restarted quickly, but the system is under heavy mist:
- the driver gets DOWN event, updates the state and schedules the work,
- the work starts to execute, reads the state,
- the driver gets UP event, updates the state, but the work is not rescheduled as it is still executing
- the worker finishes unregistering the UCSI.

>
> static void pmic_glink_ucsi_callback(const void *data, size_t len, void *priv)
>@@ -269,11 +286,12 @@ static void pmic_glink_ucsi_callback(const void *data, size_t len, void *priv)
> static void pmic_glink_ucsi_pdr_notify(void *priv, int state)
> {
> struct pmic_glink_ucsi *ucsi = priv;
>+ unsigned long flags;
>
>- if (state == SERVREG_SERVICE_STATE_UP)
>- schedule_work(&ucsi->register_work);
>- else if (state == SERVREG_SERVICE_STATE_DOWN)
>- ucsi_unregister(ucsi->ucsi);
>+ spin_lock_irqsave(&ucsi->state_lock, flags);
>+ ucsi->new_pdr_state = state;
>+ spin_unlock_irqrestore(&ucsi->state_lock, flags);
>+ schedule_work(&ucsi->register_work);
> }
>
> static void pmic_glink_ucsi_destroy(void *data)
>