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Message-ID: <A366AFBC-1775-421A-BEAC-274741DF3192@linaro.org>
Date: Mon, 19 Aug 2024 14:32:53 +0700
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Bjorn Andersson <quic_bjorande@...cinc.com>
CC: Sebastian Reichel <sre@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio <konrad.dybcio@...aro.org>,
Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Neil Armstrong <neil.armstrong@...aro.org>,
Johan Hovold <johan+linaro@...nel.org>, Chris Lew <quic_clew@...cinc.com>,
Stephen Boyd <swboyd@...omium.org>, Amit Pundir <amit.pundir@...aro.org>,
linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
stable@...r.kernel.org
Subject: Re: [PATCH 2/3] usb: typec: ucsi: Move unregister out of atomic section
On 19 August 2024 10:05:49 GMT+07:00, Bjorn Andersson <quic_bjorande@...cinc.com> wrote:
>On Mon, Aug 19, 2024 at 08:16:25AM +0700, Dmitry Baryshkov wrote:
>> On 19 August 2024 06:17:38 GMT+07:00, Bjorn Andersson <quic_bjorande@...cinc.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@...r.kernel.org
>> >Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.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.
>>
>
>I was under the impression that if we reach the point where we start
>executing the worker, then a second schedule_work() would cause the
>worker to run again. But I might be mistaken here.
I don't have full source code at hand and the docs only speak about being queued, so it is perfectly possible that I am mistaken here.
>
>What I do expect though is that if we for some reason don't start
>executing the work before the state becomes UP again, the UCSI core
>wouldn't know that the firmware has been reset.
>
>
>My proposal is to accept this risk for v6.11 (and get the benefit of
>things actually working) and then take a new swing at getting rid of all
>these workers for v6.12/13. Does that sound reasonable?
Yes, makes sense to me.
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>
>Regards,
>Bjorn
>
>>
>>
>> >
>> > 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)
>> >
>>
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