linux-kernel - Re: [PATCH] remoteproc: qcom: Fix NULL pointer in glink_subdev

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Message-ID: <ZvcJhzDmdhO/wbKq@hu-mojha-hyd.qualcomm.com>
Date: Sat, 28 Sep 2024 01:07:43 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: Bjorn Andersson <quic_bjorande@...cinc.com>
CC: Bjorn Andersson <andersson@...nel.org>,
        Mathieu Poirier
	<mathieu.poirier@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-remoteproc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] remoteproc: qcom: Fix NULL pointer in glink_subdev_stop()

On Wed, Sep 25, 2024 at 08:41:55PM -0700, Bjorn Andersson wrote:
> On Wed, Sep 25, 2024 at 04:03:51PM +0530, Mukesh Ojha wrote:
> > Multiple call to glink_subdev_stop() for the same remoteproc can happen
> > if rproc_stop() fails from Process-A that leaves the rproc state to
> > RPROC_CRASHED state later a call to recovery_store from user space in
> > Process B triggers rproc_trigger_recovery() of the same remoteproc to
> > recover it results in NULL pointer dereference issue in
> > qcom_glink_smem_unregister().
> > 
> > Fix it by having a NULL check in glink_subdev_stop().
> > 
> > 	Process-A                			Process-B
> > 
> >   fatal error interrupt happens
> > 
> >   rproc_crash_handler_work()
> >     mutex_lock_interruptible(&rproc->lock);
> >     ...
> > 
> >        rproc->state = RPROC_CRASHED;
> >     ...
> >     mutex_unlock(&rproc->lock);
> > 
> >     rproc_trigger_recovery()
> >      mutex_lock_interruptible(&rproc->lock);
> > 
> >       adsp_stop()
> >       qcom_q6v5_pas 20c00000.remoteproc: failed to shutdown: -22
> >       remoteproc remoteproc3: can't stop rproc: -22
> 
> I presume that at this point this remoteproc is in some undefined state
> and the only way to recover is for the user to reboot the machine?

Here, 50+ (5s) retry of scm shutdown is failing during decryption of
remote processor memory region, and i don't think, it is anyway to do
with remote processor state here, as a best effort more number of
retries can be tried instead of 50 or wait for some other recovery
command like recovery_store() to let it do the retry again from
beginning.

> 
> 
> The check for glink->edge avoids one pitfall following this, but I'd
> prefer to see a solution that avoids issues in this scenario in the
> remoteproc core - rather than working around side effects of this in
> different places.

Handling in a remoteproc core means we may need another state something
like "RPROC_UNKNOWN" which can be kept after one attempt of recovery
failure and checking the same during another try return immediately with
some log message.

-Mukesh