| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20230804162954.GD30679@willie-the-truck>
Date: Fri, 4 Aug 2023 17:29:55 +0100
From: Will Deacon <will@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Mark Rutland <mark.rutland@....com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v3] perf/arm-dmc620: Fix
dmc620_pmu_irqs_lock/cpu_hotplug_lock circular lock dependency
On Wed, Aug 02, 2023 at 09:44:58PM -0400, Waiman Long wrote:
>
> On 8/2/23 21:37, Waiman Long wrote:
> >
> > On 7/28/23 11:06, Will Deacon wrote:
> > > On Fri, Jul 21, 2023 at 11:17:28PM -0400, Waiman Long wrote:
> > > > The following circular locking dependency was reported when running
> > > > cpus online/offline test on an arm64 system.
> > > >
> > > > [ 84.195923] Chain exists of:
> > > > dmc620_pmu_irqs_lock --> cpu_hotplug_lock -->
> > > > cpuhp_state-down
> > > >
> > > > [ 84.207305] Possible unsafe locking scenario:
> > > >
> > > > [ 84.213212] CPU0 CPU1
> > > > [ 84.217729] ---- ----
> > > > [ 84.222247] lock(cpuhp_state-down);
> > > > [ 84.225899] lock(cpu_hotplug_lock);
> > > > [ 84.232068] lock(cpuhp_state-down);
> > > > [ 84.238237] lock(dmc620_pmu_irqs_lock);
> > > > [ 84.242236]
> > > > *** DEADLOCK ***
> > > >
> > > > The problematic locking order seems to be
> > > >
> > > > lock(dmc620_pmu_irqs_lock) --> lock(cpu_hotplug_lock)
> > > >
> > > > This locking order happens when dmc620_pmu_get_irq() is called from
> > > > dmc620_pmu_device_probe(). Since dmc620_pmu_irqs_lock is used for
> > > > protecting the dmc620_pmu_irqs structure only, we don't actually need
> > > > to hold the lock when adding a new instance to the CPU hotplug
> > > > subsystem.
> > > >
> > > > Fix this possible deadlock scenario by releasing the lock before
> > > > calling cpuhp_state_add_instance_nocalls() and reacquiring it
> > > > afterward.
> > > > To avoid the possibility of 2 racing dmc620_pmu_get_irq() calls
> > > > inserting
> > > > duplicated dmc620_pmu_irq structures with the same irq number, a dummy
> > > > entry is inserted before releasing the lock which will block a
> > > > competing
> > > > thread from inserting another irq structure of the same irq number.
> > > >
> > > > Suggested-by: Robin Murphy <robin.murphy@....com>
> > > > Signed-off-by: Waiman Long <longman@...hat.com>
> > > > ---
> > > > drivers/perf/arm_dmc620_pmu.c | 28 ++++++++++++++++++++++------
> > > > 1 file changed, 22 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/drivers/perf/arm_dmc620_pmu.c
> > > > b/drivers/perf/arm_dmc620_pmu.c
> > > > index 9d0f01c4455a..7cafd4dd4522 100644
> > > > --- a/drivers/perf/arm_dmc620_pmu.c
> > > > +++ b/drivers/perf/arm_dmc620_pmu.c
> > > > @@ -76,6 +76,7 @@ struct dmc620_pmu_irq {
> > > > refcount_t refcount;
> > > > unsigned int irq_num;
> > > > unsigned int cpu;
> > > > + unsigned int valid;
> > > > };
> > > > struct dmc620_pmu {
> > > > @@ -423,9 +424,14 @@ static struct dmc620_pmu_irq
> > > > *__dmc620_pmu_get_irq(int irq_num)
> > > > struct dmc620_pmu_irq *irq;
> > > > int ret;
> > > > - list_for_each_entry(irq, &dmc620_pmu_irqs, irqs_node)
> > > > - if (irq->irq_num == irq_num &&
> > > > refcount_inc_not_zero(&irq->refcount))
> > > > + list_for_each_entry(irq, &dmc620_pmu_irqs, irqs_node) {
> > > > + if (irq->irq_num != irq_num)
> > > > + continue;
> > > > + if (!irq->valid)
> > > > + return ERR_PTR(-EAGAIN); /* Try again later */
> > > It looks like this can bubble up to the probe() routine. Does the driver
> > > core handle -EAGAIN coming back from a probe routine?
> > Right, I should add code to handle this error condition. I think it can
> > be handled in dmc620_pmu_get_irq(). The important thing is to release
> > the mutex, wait a few ms and try again. What do you think?
> > >
> > > > + if (refcount_inc_not_zero(&irq->refcount))
> > > > return irq;
> > > > + }
> > > > irq = kzalloc(sizeof(*irq), GFP_KERNEL);
> > > > if (!irq)
> > > > @@ -447,13 +453,23 @@ static struct dmc620_pmu_irq
> > > > *__dmc620_pmu_get_irq(int irq_num)
> > > > if (ret)
> > > > goto out_free_irq;
> > > > - ret = cpuhp_state_add_instance_nocalls(cpuhp_state_num,
> > > > &irq->node);
> > > > - if (ret)
> > > > - goto out_free_irq;
> > > > -
> > > > irq->irq_num = irq_num;
> > > > list_add(&irq->irqs_node, &dmc620_pmu_irqs);
> > > > + /*
> > > > + * Release dmc620_pmu_irqs_lock before calling
> > > > + * cpuhp_state_add_instance_nocalls() and reacquire it afterward.
> > > > + */
> > > > + mutex_unlock(&dmc620_pmu_irqs_lock);
> > > > + ret = cpuhp_state_add_instance_nocalls(cpuhp_state_num,
> > > > &irq->node);
> > > > + mutex_lock(&dmc620_pmu_irqs_lock);
> > > > +
> > > > + if (ret) {
> > > > + list_del(&irq->irqs_node);
> > > > + goto out_free_irq;
> > > > + }
> > > > +
> > > > + irq->valid = true;
> > > Do you actually need a new flag here, or could we use a refcount of zero
> > > to indicate that the irq descriptor is still being constructed?
> >
> > A refcount of zero can also mean that an existing irq is about to be
> > removed. Right? So I don't think we can use that for this purpose.
> > Besides, there is a 4-byte hole in the structure anyway for arm64.
>
> Alternatively, I can use a special reference count value, say -1, to signal
> that the irq is not valid yet. What do you think?
If the device is being removed, we should teardown the irq handler first,
so I don't see why the refcount isn't the right thing.
Will
Powered by blists - more mailing lists