Re: [Intel-gfx] [PATCH 1/3] drm/i915: Separate wakeref tracking

[Andrzej Hajda <andrzej.hajda@xxxxxxxxx>]

On 27.02.2023 12:50, Jani Nikula wrote:
> On Fri, 24 Feb 2023, Andrzej Hajda <andrzej.hajda@xxxxxxxxx> wrote:
> > From: Chris Wilson <chris.p.wilson@xxxxxxxxx>
> >
> > Extract the callstack tracking of intel_runtime_pm.c into its own
> > utility so that that we can reuse it for other online debugging of
> > scoped wakerefs.
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/Kconfig.debug           |   9 +
> >   drivers/gpu/drm/i915/Makefile                |   4 +
> >   drivers/gpu/drm/i915/intel_runtime_pm.c      | 244 +++------------------------
> >   drivers/gpu/drm/i915/intel_runtime_pm.h      |  10 +-
> >   drivers/gpu/drm/i915/intel_wakeref.h         |   6 +-
> >   drivers/gpu/drm/i915/intel_wakeref_tracker.c | 234 +++++++++++++++++++++++++
> >   drivers/gpu/drm/i915/intel_wakeref_tracker.h |  76 +++++++++
> >   7 files changed, 355 insertions(+), 228 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
> > index 93dfb7ed970547..5fde52107e3b44 100644
> > --- a/drivers/gpu/drm/i915/Kconfig.debug
> > +++ b/drivers/gpu/drm/i915/Kconfig.debug
> > @@ -25,6 +25,7 @@ config DRM_I915_DEBUG
> >   	select PREEMPT_COUNT
> >   	select I2C_CHARDEV
> >   	select STACKDEPOT
> > +	select STACKTRACE
> >   	select DRM_DP_AUX_CHARDEV
> >   	select X86_MSR # used by igt/pm_rpm
> >   	select DRM_VGEM # used by igt/prime_vgem (dmabuf interop checks)
> > @@ -37,6 +38,7 @@ config DRM_I915_DEBUG
> >   	select DRM_I915_DEBUG_GEM
> >   	select DRM_I915_DEBUG_GEM_ONCE
> >   	select DRM_I915_DEBUG_MMIO
> > +	select DRM_I915_TRACK_WAKEREF
> >   	select DRM_I915_DEBUG_RUNTIME_PM
> >   	select DRM_I915_SW_FENCE_DEBUG_OBJECTS
> >   	select DRM_I915_SELFTEST
> > @@ -227,11 +229,18 @@ config DRM_I915_DEBUG_VBLANK_EVADE
> >   
> >   	  If in doubt, say "N".
> >   
> > +config DRM_I915_TRACK_WAKEREF
> > +	depends on STACKDEPOT
> > +	depends on STACKTRACE
> > +	bool
> > +
> >   config DRM_I915_DEBUG_RUNTIME_PM
> >   	bool "Enable extra state checking for runtime PM"
> >   	depends on DRM_I915
> >   	default n
> >   	select STACKDEPOT
> > +	select STACKTRACE
> > +	select DRM_I915_TRACK_WAKEREF
> >   	help
> >   	  Choose this option to turn on extra state checking for the
> >   	  runtime PM functionality. This may introduce overhead during
> > diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> > index b2f91a1f826858..42daff6d575a82 100644
> > --- a/drivers/gpu/drm/i915/Makefile
> > +++ b/drivers/gpu/drm/i915/Makefile
> > @@ -81,6 +81,10 @@ i915-$(CONFIG_DEBUG_FS) += \
> >   	i915_debugfs_params.o \
> >   	display/intel_display_debugfs.o \
> >   	display/intel_pipe_crc.o
> > +
> > +i915-$(CONFIG_DRM_I915_TRACK_WAKEREF) += \
> > +	intel_wakeref_tracker.o
> > +
> >   i915-$(CONFIG_PERF_EVENTS) += i915_pmu.o
> >   
> >   # "Graphics Technology" (aka we talk to the gpu)
> > diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
> > index 129746713d072f..72887e2bb03c21 100644
> > --- a/drivers/gpu/drm/i915/intel_runtime_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
> > @@ -52,182 +52,37 @@
> >   
> >   #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_RUNTIME_PM)
> >   
> > -#include <linux/sort.h>
> > -
> > -#define STACKDEPTH 8
> > -
> > -static noinline depot_stack_handle_t __save_depot_stack(void)
> > -{
> > -	unsigned long entries[STACKDEPTH];
> > -	unsigned int n;
> > -
> > -	n = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
> > -	return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN);
> > -}
> > -
> >   static void init_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm)
> >   {
> > -	spin_lock_init(&rpm->debug.lock);
> > -	stack_depot_init();
> > +	intel_wakeref_tracker_init(&rpm->debug);
> >   }
> >   
> > -static noinline depot_stack_handle_t
> > +static intel_wakeref_t
> >   track_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm)
> >   {
> > -	depot_stack_handle_t stack, *stacks;
> > -	unsigned long flags;
> > -
> > -	if (rpm->no_wakeref_tracking)
> > -		return -1;
> > -
> > -	stack = __save_depot_stack();
> > -	if (!stack)
> > +	if (!rpm->available)
> >   		return -1;
> >   
> > -	spin_lock_irqsave(&rpm->debug.lock, flags);
> > -
> > -	if (!rpm->debug.count)
> > -		rpm->debug.last_acquire = stack;
> > -
> > -	stacks = krealloc(rpm->debug.owners,
> > -			  (rpm->debug.count + 1) * sizeof(*stacks),
> > -			  GFP_NOWAIT | __GFP_NOWARN);
> > -	if (stacks) {
> > -		stacks[rpm->debug.count++] = stack;
> > -		rpm->debug.owners = stacks;
> > -	} else {
> > -		stack = -1;
> > -	}
> > -
> > -	spin_unlock_irqrestore(&rpm->debug.lock, flags);
> > -
> > -	return stack;
> > +	return intel_wakeref_tracker_add(&rpm->debug);
> >   }
> >   
> >   static void untrack_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm,
> > -					     depot_stack_handle_t stack)
> > +					     intel_wakeref_t wakeref)
> >   {
> > -	struct drm_i915_private *i915 = container_of(rpm,
> > -						     struct drm_i915_private,
> > -						     runtime_pm);
> > -	unsigned long flags, n;
> > -	bool found = false;
> > -
> > -	if (unlikely(stack == -1))
> > -		return;
> > -
> > -	spin_lock_irqsave(&rpm->debug.lock, flags);
> > -	for (n = rpm->debug.count; n--; ) {
> > -		if (rpm->debug.owners[n] == stack) {
> > -			memmove(rpm->debug.owners + n,
> > -				rpm->debug.owners + n + 1,
> > -				(--rpm->debug.count - n) * sizeof(stack));
> > -			found = true;
> > -			break;
> > -		}
> > -	}
> > -	spin_unlock_irqrestore(&rpm->debug.lock, flags);
> > -
> > -	if (drm_WARN(&i915->drm, !found,
> > -		     "Unmatched wakeref (tracking %lu), count %u\n",
> > -		     rpm->debug.count, atomic_read(&rpm->wakeref_count))) {
> > -		char *buf;
> > -
> > -		buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN);
> > -		if (!buf)
> > -			return;
> > -
> > -		stack_depot_snprint(stack, buf, PAGE_SIZE, 2);
> > -		DRM_DEBUG_DRIVER("wakeref %x from\n%s", stack, buf);
> > -
> > -		stack = READ_ONCE(rpm->debug.last_release);
> > -		if (stack) {
> > -			stack_depot_snprint(stack, buf, PAGE_SIZE, 2);
> > -			DRM_DEBUG_DRIVER("wakeref last released at\n%s", buf);
> > -		}
> > -
> > -		kfree(buf);
> > -	}
> > +	intel_wakeref_tracker_remove(&rpm->debug, wakeref);
> >   }
> >   
> > -static int cmphandle(const void *_a, const void *_b)
> > +static void untrack_all_intel_runtime_pm_wakerefs(struct intel_runtime_pm *rpm)
> >   {
> > -	const depot_stack_handle_t * const a = _a, * const b = _b;
> > +	struct drm_printer p = drm_debug_printer("i915");
> >   
> > -	if (*a < *b)
> > -		return -1;
> > -	else if (*a > *b)
> > -		return 1;
> > -	else
> > -		return 0;
> > -}
> > -
> > -static void
> > -__print_intel_runtime_pm_wakeref(struct drm_printer *p,
> > -				 const struct intel_runtime_pm_debug *dbg)
> > -{
> > -	unsigned long i;
> > -	char *buf;
> > -
> > -	buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN);
> > -	if (!buf)
> > -		return;
> > -
> > -	if (dbg->last_acquire) {
> > -		stack_depot_snprint(dbg->last_acquire, buf, PAGE_SIZE, 2);
> > -		drm_printf(p, "Wakeref last acquired:\n%s", buf);
> > -	}
> > -
> > -	if (dbg->last_release) {
> > -		stack_depot_snprint(dbg->last_release, buf, PAGE_SIZE, 2);
> > -		drm_printf(p, "Wakeref last released:\n%s", buf);
> > -	}
> > -
> > -	drm_printf(p, "Wakeref count: %lu\n", dbg->count);
> > -
> > -	sort(dbg->owners, dbg->count, sizeof(*dbg->owners), cmphandle, NULL);
> > -
> > -	for (i = 0; i < dbg->count; i++) {
> > -		depot_stack_handle_t stack = dbg->owners[i];
> > -		unsigned long rep;
> > -
> > -		rep = 1;
> > -		while (i + 1 < dbg->count && dbg->owners[i + 1] == stack)
> > -			rep++, i++;
> > -		stack_depot_snprint(stack, buf, PAGE_SIZE, 2);
> > -		drm_printf(p, "Wakeref x%lu taken at:\n%s", rep, buf);
> > -	}
> > -
> > -	kfree(buf);
> > -}
> > -
> > -static noinline void
> > -__untrack_all_wakerefs(struct intel_runtime_pm_debug *debug,
> > -		       struct intel_runtime_pm_debug *saved)
> > -{
> > -	*saved = *debug;
> > -
> > -	debug->owners = NULL;
> > -	debug->count = 0;
> > -	debug->last_release = __save_depot_stack();
> > -}
> > -
> > -static void
> > -dump_and_free_wakeref_tracking(struct intel_runtime_pm_debug *debug)
> > -{
> > -	if (debug->count) {
> > -		struct drm_printer p = drm_debug_printer("i915");
> > -
> > -		__print_intel_runtime_pm_wakeref(&p, debug);
> > -	}
> > -
> > -	kfree(debug->owners);
> > +	intel_wakeref_tracker_reset(&rpm->debug, &p);
> >   }
> >   
> >   static noinline void
> >   __intel_wakeref_dec_and_check_tracking(struct intel_runtime_pm *rpm)
> >   {
> > -	struct intel_runtime_pm_debug dbg = {};
> > +	struct intel_wakeref_tracker saved;
> >   	unsigned long flags;
> >   
> >   	if (!atomic_dec_and_lock_irqsave(&rpm->wakeref_count,
> > @@ -235,60 +90,21 @@ __intel_wakeref_dec_and_check_tracking(struct intel_runtime_pm *rpm)
> >   					 flags))
> >   		return;
> >   
> > -	__untrack_all_wakerefs(&rpm->debug, &dbg);
> > +	saved = __intel_wakeref_tracker_reset(&rpm->debug);
> >   	spin_unlock_irqrestore(&rpm->debug.lock, flags);
> >   
> > -	dump_and_free_wakeref_tracking(&dbg);
> > -}
> > -
> > -static noinline void
> > -untrack_all_intel_runtime_pm_wakerefs(struct intel_runtime_pm *rpm)
> > -{
> > -	struct intel_runtime_pm_debug dbg = {};
> > -	unsigned long flags;
> > -
> > -	spin_lock_irqsave(&rpm->debug.lock, flags);
> > -	__untrack_all_wakerefs(&rpm->debug, &dbg);
> > -	spin_unlock_irqrestore(&rpm->debug.lock, flags);
> > +	if (saved.count) {
> > +		struct drm_printer p = drm_debug_printer("i915");
> >   
> > -	dump_and_free_wakeref_tracking(&dbg);
> > +		__intel_wakeref_tracker_show(&saved, &p);
> > +		intel_wakeref_tracker_fini(&saved);
> > +	}
> >   }
> >   
> >   void print_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm,
> >   				    struct drm_printer *p)
> >   {
> > -	struct intel_runtime_pm_debug dbg = {};
> > -
> > -	do {
> > -		unsigned long alloc = dbg.count;
> > -		depot_stack_handle_t *s;
> > -
> > -		spin_lock_irq(&rpm->debug.lock);
> > -		dbg.count = rpm->debug.count;
> > -		if (dbg.count <= alloc) {
> > -			memcpy(dbg.owners,
> > -			       rpm->debug.owners,
> > -			       dbg.count * sizeof(*s));
> > -		}
> > -		dbg.last_acquire = rpm->debug.last_acquire;
> > -		dbg.last_release = rpm->debug.last_release;
> > -		spin_unlock_irq(&rpm->debug.lock);
> > -		if (dbg.count <= alloc)
> > -			break;
> > -
> > -		s = krealloc(dbg.owners,
> > -			     dbg.count * sizeof(*s),
> > -			     GFP_NOWAIT | __GFP_NOWARN);
> > -		if (!s)
> > -			goto out;
> > -
> > -		dbg.owners = s;
> > -	} while (1);
> > -
> > -	__print_intel_runtime_pm_wakeref(p, &dbg);
> > -
> > -out:
> > -	kfree(dbg.owners);
> > +	intel_wakeref_tracker_show(&rpm->debug, p);
> >   }
> >   
> >   #else
> > @@ -297,14 +113,14 @@ static void init_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm)
> >   {
> >   }
> >   
> > -static depot_stack_handle_t
> > +static intel_wakeref_t
> >   track_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm)
> >   {
> >   	return -1;
> >   }
> >   
> >   static void untrack_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm,
> > -					     intel_wakeref_t wref)
> > +					     intel_wakeref_t wakeref)
> >   {
> >   }
> >   
> > @@ -349,9 +165,8 @@ intel_runtime_pm_release(struct intel_runtime_pm *rpm, int wakelock)
> >   static intel_wakeref_t __intel_runtime_pm_get(struct intel_runtime_pm *rpm,
> >   					      bool wakelock)
> >   {
> > -	struct drm_i915_private *i915 = container_of(rpm,
> > -						     struct drm_i915_private,
> > -						     runtime_pm);
> > +	struct drm_i915_private *i915 =
> > +		container_of(rpm, struct drm_i915_private, runtime_pm);
> >   	int ret;
> >   
> >   	ret = pm_runtime_get_sync(rpm->kdev);
> > @@ -556,9 +371,8 @@ void intel_runtime_pm_put(struct intel_runtime_pm *rpm, intel_wakeref_t wref)
> >    */
> >   void intel_runtime_pm_enable(struct intel_runtime_pm *rpm)
> >   {
> > -	struct drm_i915_private *i915 = container_of(rpm,
> > -						     struct drm_i915_private,
> > -						     runtime_pm);
> > +	struct drm_i915_private *i915 =
> > +		container_of(rpm, struct drm_i915_private, runtime_pm);
> >   	struct device *kdev = rpm->kdev;
> >   
> >   	/*
> > @@ -611,9 +425,8 @@ void intel_runtime_pm_enable(struct intel_runtime_pm *rpm)
> >   
> >   void intel_runtime_pm_disable(struct intel_runtime_pm *rpm)
> >   {
> > -	struct drm_i915_private *i915 = container_of(rpm,
> > -						     struct drm_i915_private,
> > -						     runtime_pm);
> > +	struct drm_i915_private *i915 =
> > +		container_of(rpm, struct drm_i915_private, runtime_pm);
> >   	struct device *kdev = rpm->kdev;
> >   
> >   	/* Transfer rpm ownership back to core */
> > @@ -628,9 +441,8 @@ void intel_runtime_pm_disable(struct intel_runtime_pm *rpm)
> >   
> >   void intel_runtime_pm_driver_release(struct intel_runtime_pm *rpm)
> >   {
> > -	struct drm_i915_private *i915 = container_of(rpm,
> > -						     struct drm_i915_private,
> > -						     runtime_pm);
> > +	struct drm_i915_private *i915 =
> > +		container_of(rpm, struct drm_i915_private, runtime_pm);
> >   	int count = atomic_read(&rpm->wakeref_count);
> >   
> >   	intel_wakeref_auto_fini(&rpm->userfault_wakeref);
> > @@ -646,7 +458,7 @@ void intel_runtime_pm_driver_release(struct intel_runtime_pm *rpm)
> >   void intel_runtime_pm_init_early(struct intel_runtime_pm *rpm)
> >   {
> >   	struct drm_i915_private *i915 =
> > -			container_of(rpm, struct drm_i915_private, runtime_pm);
> > +		container_of(rpm, struct drm_i915_private, runtime_pm);
>
> Lots of unrelated changes above that should be separate patches.


OK


> >   	struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
> >   	struct device *kdev = &pdev->dev;
> >   
> > diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.h b/drivers/gpu/drm/i915/intel_runtime_pm.h
> > index e592e8d6499a1f..a8dc2baf79844f 100644
> > --- a/drivers/gpu/drm/i915/intel_runtime_pm.h
> > +++ b/drivers/gpu/drm/i915/intel_runtime_pm.h
> > @@ -83,15 +83,7 @@ struct intel_runtime_pm {
> >   	 * paired rpm_put) we can remove corresponding pairs of and keep
> >   	 * the array trimmed to active wakerefs.
> >   	 */
> > -	struct intel_runtime_pm_debug {
> > -		spinlock_t lock;
> > -
> > -		depot_stack_handle_t last_acquire;
> > -		depot_stack_handle_t last_release;
> > -
> > -		depot_stack_handle_t *owners;
> > -		unsigned long count;
> > -	} debug;
> > +	struct intel_wakeref_tracker debug;
>
> There's a lot going on in the patch all around. Adding the struct to a
> separate file could maybe be an individual patch to simplify the actual
> changes.

Hmm, the patch abstracts out wakeref_tracker from rpm to separate 
'library'. In this context the change above looks quite natural and 
atomic for me.

> This doesn't include the file that defines struct intel_wakeref_tracker;
> it's included via intel_wakeref.h. But only if
>
> >   #endif
> >   };
> >   
> > diff --git a/drivers/gpu/drm/i915/intel_wakeref.h b/drivers/gpu/drm/i915/intel_wakeref.h
> > index 71b8a63f6f104d..20720fbcc28d46 100644
> > --- a/drivers/gpu/drm/i915/intel_wakeref.h
> > +++ b/drivers/gpu/drm/i915/intel_wakeref.h
> > @@ -17,7 +17,9 @@
> >   #include <linux/timer.h>
> >   #include <linux/workqueue.h>
> >   
> > -#if IS_ENABLED(CONFIG_DRM_I915_DEBUG)
> > +#include "intel_wakeref_tracker.h"
> > +
> > +#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_WAKEREF)
> >   #define INTEL_WAKEREF_BUG_ON(expr) BUG_ON(expr)
> >   #else
> >   #define INTEL_WAKEREF_BUG_ON(expr) BUILD_BUG_ON_INVALID(expr)
> > @@ -26,8 +28,6 @@
> >   struct intel_runtime_pm;
> >   struct intel_wakeref;
> >   
> > -typedef depot_stack_handle_t intel_wakeref_t;
> > -
> >   struct intel_wakeref_ops {
> >   	int (*get)(struct intel_wakeref *wf);
> >   	int (*put)(struct intel_wakeref *wf);
> > diff --git a/drivers/gpu/drm/i915/intel_wakeref_tracker.c b/drivers/gpu/drm/i915/intel_wakeref_tracker.c
> > new file mode 100644
> > index 00000000000000..a0bcef13a1085a
> > --- /dev/null
> > +++ b/drivers/gpu/drm/i915/intel_wakeref_tracker.c
> > @@ -0,0 +1,234 @@
> > +// SPDX-License-Identifier: MIT
> > +/*
> > + * Copyright © 2021 Intel Corporation
> > + */
> > +
> > +#include <linux/slab.h>
> > +#include <linux/stackdepot.h>
> > +#include <linux/stacktrace.h>
> > +#include <linux/sort.h>
> > +
> > +#include <drm/drm_print.h>
> > +
> > +#include "intel_wakeref.h"
>
> This should really include the corresponding .h
> i.e. intel_wakeref_tracker.h too. Now it gets included via
> intel_wakeref.h but I'm not sure why.

Apparently some leftover, will fix it.

Regards
Andrzej


> > +
> > +#define STACKDEPTH 8
> > +
> > +static noinline depot_stack_handle_t __save_depot_stack(void)
> > +{
> > +	unsigned long entries[STACKDEPTH];
> > +	unsigned int n;
> > +
> > +	n = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
> > +	return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN);
> > +}
> > +
> > +static void __print_depot_stack(depot_stack_handle_t stack,
> > +				char *buf, int sz, int indent)
> > +{
> > +	unsigned long *entries;
> > +	unsigned int nr_entries;
> > +
> > +	nr_entries = stack_depot_fetch(stack, &entries);
> > +	stack_trace_snprint(buf, sz, entries, nr_entries, indent);
> > +}
> > +
> > +static int cmphandle(const void *_a, const void *_b)
> > +{
> > +	const depot_stack_handle_t * const a = _a, * const b = _b;
> > +
> > +	if (*a < *b)
> > +		return -1;
> > +	else if (*a > *b)
> > +		return 1;
> > +	else
> > +		return 0;
> > +}
> > +
> > +void
> > +__intel_wakeref_tracker_show(const struct intel_wakeref_tracker *w,
> > +			     struct drm_printer *p)
> > +{
> > +	unsigned long i;
> > +	char *buf;
> > +
> > +	buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN);
> > +	if (!buf)
> > +		return;
> > +
> > +	if (w->last_acquire) {
> > +		__print_depot_stack(w->last_acquire, buf, PAGE_SIZE, 2);
> > +		drm_printf(p, "Wakeref last acquired:\n%s", buf);
> > +	}
> > +
> > +	if (w->last_release) {
> > +		__print_depot_stack(w->last_release, buf, PAGE_SIZE, 2);
> > +		drm_printf(p, "Wakeref last released:\n%s", buf);
> > +	}
> > +
> > +	drm_printf(p, "Wakeref count: %lu\n", w->count);
> > +
> > +	sort(w->owners, w->count, sizeof(*w->owners), cmphandle, NULL);
> > +
> > +	for (i = 0; i < w->count; i++) {
> > +		depot_stack_handle_t stack = w->owners[i];
> > +		unsigned long rep;
> > +
> > +		rep = 1;
> > +		while (i + 1 < w->count && w->owners[i + 1] == stack)
> > +			rep++, i++;
> > +		__print_depot_stack(stack, buf, PAGE_SIZE, 2);
> > +		drm_printf(p, "Wakeref x%lu taken at:\n%s", rep, buf);
> > +	}
> > +
> > +	kfree(buf);
> > +}
> > +
> > +void intel_wakeref_tracker_show(struct intel_wakeref_tracker *w,
> > +				struct drm_printer *p)
> > +{
> > +	struct intel_wakeref_tracker tmp = {};
> > +
> > +	do {
> > +		unsigned long alloc = tmp.count;
> > +		depot_stack_handle_t *s;
> > +
> > +		spin_lock_irq(&w->lock);
> > +		tmp.count = w->count;
> > +		if (tmp.count <= alloc)
> > +			memcpy(tmp.owners, w->owners, tmp.count * sizeof(*s));
> > +		tmp.last_acquire = w->last_acquire;
> > +		tmp.last_release = w->last_release;
> > +		spin_unlock_irq(&w->lock);
> > +		if (tmp.count <= alloc)
> > +			break;
> > +
> > +		s = krealloc(tmp.owners,
> > +			     tmp.count * sizeof(*s),
> > +			     GFP_NOWAIT | __GFP_NOWARN);
> > +		if (!s)
> > +			goto out;
> > +
> > +		tmp.owners = s;
> > +	} while (1);
> > +
> > +	__intel_wakeref_tracker_show(&tmp, p);
> > +
> > +out:
> > +	intel_wakeref_tracker_fini(&tmp);
> > +}
> > +
> > +intel_wakeref_t intel_wakeref_tracker_add(struct intel_wakeref_tracker *w)
> > +{
> > +	depot_stack_handle_t stack, *stacks;
> > +	unsigned long flags;
> > +
> > +	stack = __save_depot_stack();
> > +	if (!stack)
> > +		return -1;
> > +
> > +	spin_lock_irqsave(&w->lock, flags);
> > +
> > +	if (!w->count)
> > +		w->last_acquire = stack;
> > +
> > +	stacks = krealloc(w->owners,
> > +			  (w->count + 1) * sizeof(*stacks),
> > +			  GFP_NOWAIT | __GFP_NOWARN);
> > +	if (stacks) {
> > +		stacks[w->count++] = stack;
> > +		w->owners = stacks;
> > +	} else {
> > +		stack = -1;
> > +	}
> > +
> > +	spin_unlock_irqrestore(&w->lock, flags);
> > +
> > +	return stack;
> > +}
> > +
> > +void intel_wakeref_tracker_remove(struct intel_wakeref_tracker *w,
> > +				  intel_wakeref_t stack)
> > +{
> > +	unsigned long flags, n;
> > +	bool found = false;
> > +
> > +	if (unlikely(stack == -1))
> > +		return;
> > +
> > +	spin_lock_irqsave(&w->lock, flags);
> > +	for (n = w->count; n--; ) {
> > +		if (w->owners[n] == stack) {
> > +			memmove(w->owners + n,
> > +				w->owners + n + 1,
> > +				(--w->count - n) * sizeof(stack));
> > +			found = true;
> > +			break;
> > +		}
> > +	}
> > +	spin_unlock_irqrestore(&w->lock, flags);
> > +
> > +	if (WARN(!found,
> > +		 "Unmatched wakeref %x, tracking %lu\n",
> > +		 stack, w->count)) {
> > +		char *buf;
> > +
> > +		buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN);
> > +		if (!buf)
> > +			return;
> > +
> > +		__print_depot_stack(stack, buf, PAGE_SIZE, 2);
> > +		pr_err("wakeref %x from\n%s", stack, buf);
> > +
> > +		stack = READ_ONCE(w->last_release);
> > +		if (stack && !w->count) {
> > +			__print_depot_stack(stack, buf, PAGE_SIZE, 2);
> > +			pr_err("wakeref last released at\n%s", buf);
> > +		}
> > +
> > +		kfree(buf);
> > +	}
> > +}
> > +
> > +struct intel_wakeref_tracker
> > +__intel_wakeref_tracker_reset(struct intel_wakeref_tracker *w)
> > +{
> > +	struct intel_wakeref_tracker saved;
> > +
> > +	lockdep_assert_held(&w->lock);
> > +
> > +	saved = *w;
> > +
> > +	w->owners = NULL;
> > +	w->count = 0;
> > +	w->last_release = __save_depot_stack();
> > +
> > +	return saved;
> > +}
> > +
> > +void intel_wakeref_tracker_reset(struct intel_wakeref_tracker *w,
> > +				 struct drm_printer *p)
> > +{
> > +	struct intel_wakeref_tracker tmp;
> > +
> > +	spin_lock_irq(&w->lock);
> > +	tmp = __intel_wakeref_tracker_reset(w);
> > +	spin_unlock_irq(&w->lock);
> > +
> > +	if (tmp.count)
> > +		__intel_wakeref_tracker_show(&tmp, p);
> > +
> > +	intel_wakeref_tracker_fini(&tmp);
> > +}
> > +
> > +void intel_wakeref_tracker_init(struct intel_wakeref_tracker *w)
> > +{
> > +	memset(w, 0, sizeof(*w));
> > +	spin_lock_init(&w->lock);
> > +	stack_depot_init();
> > +}
> > +
> > +void intel_wakeref_tracker_fini(struct intel_wakeref_tracker *w)
> > +{
> > +	kfree(w->owners);
> > +}
> > diff --git a/drivers/gpu/drm/i915/intel_wakeref_tracker.h b/drivers/gpu/drm/i915/intel_wakeref_tracker.h
> > new file mode 100644
> > index 00000000000000..61df68e28c0fbf
> > --- /dev/null
> > +++ b/drivers/gpu/drm/i915/intel_wakeref_tracker.h
> > @@ -0,0 +1,76 @@
> > +/* SPDX-License-Identifier: MIT */
> > +/*
> > + * Copyright © 2019 Intel Corporation
> > + */
> > +
> > +#ifndef INTEL_WAKEREF_TRACKER_H
> > +#define INTEL_WAKEREF_TRACKER_H
> > +
> > +#include <linux/kconfig.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/stackdepot.h>
> > +
> > +typedef depot_stack_handle_t intel_wakeref_t;
> > +
> > +struct drm_printer;
> > +
> > +struct intel_wakeref_tracker {
> > +	spinlock_t lock;
> > +
> > +	depot_stack_handle_t last_acquire;
> > +	depot_stack_handle_t last_release;
> > +
> > +	depot_stack_handle_t *owners;
> > +	unsigned long count;
> > +};
> > +
> > +#if IS_ENABLED(CONFIG_DRM_I915_TRACK_WAKEREF)
> > +
> > +void intel_wakeref_tracker_init(struct intel_wakeref_tracker *w);
> > +void intel_wakeref_tracker_fini(struct intel_wakeref_tracker *w);
> > +
> > +intel_wakeref_t intel_wakeref_tracker_add(struct intel_wakeref_tracker *w);
> > +void intel_wakeref_tracker_remove(struct intel_wakeref_tracker *w,
> > +			   intel_wakeref_t handle);
> > +
> > +struct intel_wakeref_tracker
> > +__intel_wakeref_tracker_reset(struct intel_wakeref_tracker *w);
> > +void intel_wakeref_tracker_reset(struct intel_wakeref_tracker *w,
> > +				 struct drm_printer *p);
> > +
> > +void __intel_wakeref_tracker_show(const struct intel_wakeref_tracker *w,
> > +				  struct drm_printer *p);
> > +void intel_wakeref_tracker_show(struct intel_wakeref_tracker *w,
> > +				struct drm_printer *p);
> > +
> > +#else
> > +
> > +static inline void intel_wakeref_tracker_init(struct intel_wakeref_tracker *w) {}
> > +static inline void intel_wakeref_tracker_fini(struct intel_wakeref_tracker *w) {}
> > +
> > +static inline intel_wakeref_t
> > +intel_wakeref_tracker_add(struct intel_wakeref_tracker *w)
> > +{
> > +	return -1;
> > +}
> > +
> > +static inline void
> > +intel_wakeref_untrack_remove(struct intel_wakeref_tracker *w, intel_wakeref_t handle) {}
> > +
> > +static inline struct intel_wakeref_tracker
> > +__intel_wakeref_tracker_reset(struct intel_wakeref_tracker *w)
> > +{
> > +	return (struct intel_wakeref_tracker){};
> > +}
> > +
> > +static inline void intel_wakeref_tracker_reset(struct intel_wakeref_tracker *w,
> > +					       struct drm_printer *p)
> > +{
> > +}
> > +
> > +static inline void __intel_wakeref_tracker_show(const struct intel_wakeref_tracker *w, struct drm_printer *p) {}
> > +static inline void intel_wakeref_tracker_show(struct intel_wakeref_tracker *w, struct drm_printer *p) {}
> > +
> > +#endif
> > +
> > +#endif /* INTEL_WAKEREF_TRACKER_H */