| Message ID | 20250402011832.2970072-2-yabinc@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | coresight: catu: Introduce refcount and spinlock for enabling/disabling | expand |
On Tue, Apr 1, 2025 at 6:19 PM Yabin Cui <yabinc@google.com> wrote: > > When tracing ETM data on multiple CPUs concurrently via the > perf interface, the CATU device is shared across different CPU > paths. This can lead to race conditions when multiple CPUs attempt > to enable or disable the CATU device simultaneously. > > To address these race conditions, this patch introduces the > following changes: > > 1. The enable and disable operations for the CATU device are not > reentrant. Therefore, a spinlock is added to ensure that only > one CPU can enable or disable a given CATU device at any point > in time. > > 2. A reference counter is used to manage the enable/disable state > of the CATU device. The device is enabled when the first CPU > requires it and is only disabled when the last CPU finishes > using it. This ensures the device remains active as long as at > least one CPU needs it. > > Signed-off-by: Yabin Cui <yabinc@google.com> > --- > drivers/hwtracing/coresight/coresight-catu.c | 27 ++++++++++++++------ > drivers/hwtracing/coresight/coresight-catu.h | 1 + > 2 files changed, 20 insertions(+), 8 deletions(-) > > diff --git a/drivers/hwtracing/coresight/coresight-catu.c b/drivers/hwtracing/coresight/coresight-catu.c > index fa170c966bc3..b1d490dd7249 100644 > --- a/drivers/hwtracing/coresight/coresight-catu.c > +++ b/drivers/hwtracing/coresight/coresight-catu.c > @@ -458,12 +458,17 @@ static int catu_enable_hw(struct catu_drvdata *drvdata, enum cs_mode cs_mode, > static int catu_enable(struct coresight_device *csdev, enum cs_mode mode, > void *data) > { > - int rc; > + int rc = 0; > struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev); > + guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock); > > - CS_UNLOCK(catu_drvdata->base); > - rc = catu_enable_hw(catu_drvdata, mode, data); > - CS_LOCK(catu_drvdata->base); > + if (csdev->refcnt == 0) { > + CS_UNLOCK(catu_drvdata->base); > + rc = catu_enable_hw(catu_drvdata, mode, data); > + CS_LOCK(catu_drvdata->base); > + } > + if (!rc) > + csdev->refcnt++; > return rc; > } > > @@ -486,12 +491,17 @@ static int catu_disable_hw(struct catu_drvdata *drvdata) > > static int catu_disable(struct coresight_device *csdev, void *__unused) > { > - int rc; > + int rc = 0; > struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev); > + guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock); > > - CS_UNLOCK(catu_drvdata->base); > - rc = catu_disable_hw(catu_drvdata); > - CS_LOCK(catu_drvdata->base); > + if (--csdev->refcnt == 0) { > + CS_UNLOCK(catu_drvdata->base); > + rc = catu_disable_hw(catu_drvdata); > + CS_LOCK(catu_drvdata->base); > + } else { > + rc = -EBUSY; > + } > return rc; > } > > @@ -550,6 +560,7 @@ static int __catu_probe(struct device *dev, struct resource *res) > dev->platform_data = pdata; > > drvdata->base = base; > + raw_spin_lock_init(&drvdata->spinlock); > catu_desc.access = CSDEV_ACCESS_IOMEM(base); > catu_desc.pdata = pdata; > catu_desc.dev = dev; > diff --git a/drivers/hwtracing/coresight/coresight-catu.h b/drivers/hwtracing/coresight/coresight-catu.h > index 141feac1c14b..755776cd19c5 100644 > --- a/drivers/hwtracing/coresight/coresight-catu.h > +++ b/drivers/hwtracing/coresight/coresight-catu.h > @@ -65,6 +65,7 @@ struct catu_drvdata { > void __iomem *base; > struct coresight_device *csdev; > int irq; > + raw_spinlock_t spinlock; > }; > > #define CATU_REG32(name, offset) \ > -- > 2.49.0.472.ge94155a9ec-goog >
Hi Yabin, On Tue, Apr 01, 2025 at 06:21:59PM -0700, Yabin Cui wrote: [...] > > @@ -486,12 +491,17 @@ static int catu_disable_hw(struct catu_drvdata *drvdata) > > > > static int catu_disable(struct coresight_device *csdev, void *__unused) > > { > > - int rc; > > + int rc = 0; > > struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev); > > + guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock); > > > > - CS_UNLOCK(catu_drvdata->base); > > - rc = catu_disable_hw(catu_drvdata); > > - CS_LOCK(catu_drvdata->base); > > + if (--csdev->refcnt == 0) { > > + CS_UNLOCK(catu_drvdata->base); > > + rc = catu_disable_hw(catu_drvdata); > > + CS_LOCK(catu_drvdata->base); > > + } else { > > + rc = -EBUSY; This is not an error if the decremented reference counter is not zero. It should return 0. Otherwise, the change looks good to me. Thanks, Leo
diff --git a/drivers/hwtracing/coresight/coresight-catu.c b/drivers/hwtracing/coresight/coresight-catu.c index fa170c966bc3..b1d490dd7249 100644 --- a/drivers/hwtracing/coresight/coresight-catu.c +++ b/drivers/hwtracing/coresight/coresight-catu.c @@ -458,12 +458,17 @@ static int catu_enable_hw(struct catu_drvdata *drvdata, enum cs_mode cs_mode, static int catu_enable(struct coresight_device *csdev, enum cs_mode mode, void *data) { - int rc; + int rc = 0; struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev); + guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock); - CS_UNLOCK(catu_drvdata->base); - rc = catu_enable_hw(catu_drvdata, mode, data); - CS_LOCK(catu_drvdata->base); + if (csdev->refcnt == 0) { + CS_UNLOCK(catu_drvdata->base); + rc = catu_enable_hw(catu_drvdata, mode, data); + CS_LOCK(catu_drvdata->base); + } + if (!rc) + csdev->refcnt++; return rc; } @@ -486,12 +491,17 @@ static int catu_disable_hw(struct catu_drvdata *drvdata) static int catu_disable(struct coresight_device *csdev, void *__unused) { - int rc; + int rc = 0; struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev); + guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock); - CS_UNLOCK(catu_drvdata->base); - rc = catu_disable_hw(catu_drvdata); - CS_LOCK(catu_drvdata->base); + if (--csdev->refcnt == 0) { + CS_UNLOCK(catu_drvdata->base); + rc = catu_disable_hw(catu_drvdata); + CS_LOCK(catu_drvdata->base); + } else { + rc = -EBUSY; + } return rc; } @@ -550,6 +560,7 @@ static int __catu_probe(struct device *dev, struct resource *res) dev->platform_data = pdata; drvdata->base = base; + raw_spin_lock_init(&drvdata->spinlock); catu_desc.access = CSDEV_ACCESS_IOMEM(base); catu_desc.pdata = pdata; catu_desc.dev = dev; diff --git a/drivers/hwtracing/coresight/coresight-catu.h b/drivers/hwtracing/coresight/coresight-catu.h index 141feac1c14b..755776cd19c5 100644 --- a/drivers/hwtracing/coresight/coresight-catu.h +++ b/drivers/hwtracing/coresight/coresight-catu.h @@ -65,6 +65,7 @@ struct catu_drvdata { void __iomem *base; struct coresight_device *csdev; int irq; + raw_spinlock_t spinlock; }; #define CATU_REG32(name, offset) \
When tracing ETM data on multiple CPUs concurrently via the perf interface, the CATU device is shared across different CPU paths. This can lead to race conditions when multiple CPUs attempt to enable or disable the CATU device simultaneously. To address these race conditions, this patch introduces the following changes: 1. The enable and disable operations for the CATU device are not reentrant. Therefore, a spinlock is added to ensure that only one CPU can enable or disable a given CATU device at any point in time. 2. A reference counter is used to manage the enable/disable state of the CATU device. The device is enabled when the first CPU requires it and is only disabled when the last CPU finishes using it. This ensures the device remains active as long as at least one CPU needs it. Signed-off-by: Yabin Cui <yabinc@google.com> --- drivers/hwtracing/coresight/coresight-catu.c | 27 ++++++++++++++------ drivers/hwtracing/coresight/coresight-catu.h | 1 + 2 files changed, 20 insertions(+), 8 deletions(-)