Hi Daniel

Am 02.03.20 um 23:25 schrieb Daniel Vetter:
> We have lots of these. And the cleanup code tends to be of dubious
> quality. The biggest wrong pattern is that developers use devm_, which
> ties the release action to the underlying struct device, whereas
> all the userspace visible stuff attached to a drm_device can long
> outlive that one (e.g. after a hotunplug while userspace has open
> files and mmap'ed buffers). Give people what they want, but with more
> correctness.
> 
> Mostly copied from devres.c, with types adjusted to fit drm_device and
> a few simplifications - I didn't (yet) copy over everything. Since
> the types don't match code sharing looked like a hopeless endeavour.
> 
> For now it's only super simplified, no groups, you can't remove
> actions (but kfree exists, we'll need that soon). Plus all specific to
> drm_device ofc, including the logging. Which I didn't bother to make
> compile-time optional, since none of the other drm logging is compile
> time optional either.
> 
> One tricky bit here is the chicken&egg between allocating your
> drm_device structure and initiliazing it with drm_dev_init. For
> perfect onion unwinding we'd need to have the action to kfree the
> allocation registered before drm_dev_init registers any of its own
> release handlers. But drm_dev_init doesn't know where exactly the
> drm_device is emebedded into the overall structure, and by the time it
> returns it'll all be too late. And forcing drivers to be able clean up
> everything except the one kzalloc is silly.
> 
> Work around this by having a very special final_kfree pointer. This
> also avoids troubles with the list head possibly disappearing from
> underneath us when we release all resources attached to the
> drm_device.
> 
> v2: Do all the kerneldoc at the end, to avoid lots of fairly pointless
> shuffling while getting everything into shape.
> 
> v3: Add static to add/del_dr (Neil)
> Move typo fix to the right patch (Neil)
> 
> v4: Enforce contract for drmm_add_final_kfree:
> 
> Use ksize() to check that the drm_device is indeed contained somewhere
> in the final kfree(). Because we need that or the entire managed
> release logic blows up in a pile of use-after-frees. Motivated by a
> discussion with Laurent.
> 
> v5: Review from Laurent:
> - %zu instead of casting size_t
> - header guards
> - sorting of includes
> - guarding of data assignment if we didn't allocate it for a NULL
>   pointer
> - delete spurious newline
> - cast void* data parameter correctly in ->release call, no idea how
>   this even worked before
> 
> v3: Review from Sam
> - Add the kerneldoc for the managed sub-struct back in, even if it
>   doesn't show up in the generated html somehow.
> - Explain why __always_inline.
> - Fix bisectability around the final kfree() in drm_dev_relase(). This
>   is just interim code which will disappear again.
> - Some whitespace polish.
> - Add debug output when drmm_add_action or drmm_kmalloc fail.
> 
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Neil Armstrong <narmstrong@baylibre.com
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  Documentation/gpu/drm-internals.rst |   6 +
>  drivers/gpu/drm/Makefile            |   3 +-
>  drivers/gpu/drm/drm_drv.c           |  12 ++
>  drivers/gpu/drm/drm_internal.h      |   3 +
>  drivers/gpu/drm/drm_managed.c       | 186 ++++++++++++++++++++++++++++
>  include/drm/drm_device.h            |  15 +++
>  include/drm/drm_managed.h           |  30 +++++
>  include/drm/drm_print.h             |   6 +
>  8 files changed, 260 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/gpu/drm/drm_managed.c
>  create mode 100644 include/drm/drm_managed.h
> 
> diff --git a/Documentation/gpu/drm-internals.rst b/Documentation/gpu/drm-internals.rst
> index a73320576ca9..a6b6145fda78 100644
> --- a/Documentation/gpu/drm-internals.rst
> +++ b/Documentation/gpu/drm-internals.rst
> @@ -132,6 +132,12 @@ be unmapped; on many devices, the ROM address decoder is shared with
>  other BARs, so leaving it mapped could cause undesired behaviour like
>  hangs or memory corruption.
>  
> +Managed Resources
> +-----------------
> +
> +.. kernel-doc:: drivers/gpu/drm/drm_managed.c
> +   :doc: managed resources
> +
>  Bus-specific Device Registration and PCI Support
>  ------------------------------------------------
>  
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 7f72ef5e7811..183c60048307 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -17,7 +17,8 @@ drm-y       :=	drm_auth.o drm_cache.o \
>  		drm_plane.o drm_color_mgmt.o drm_print.o \
>  		drm_dumb_buffers.o drm_mode_config.o drm_vblank.o \
>  		drm_syncobj.o drm_lease.o drm_writeback.o drm_client.o \
> -		drm_client_modeset.o drm_atomic_uapi.o drm_hdcp.o
> +		drm_client_modeset.o drm_atomic_uapi.o drm_hdcp.o \
> +		drm_managed.o
>  
>  drm-$(CONFIG_DRM_LEGACY) += drm_legacy_misc.o drm_bufs.o drm_context.o drm_dma.o drm_scatter.o drm_lock.o
>  drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 9fcd6ab3c154..153050fc926c 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -629,6 +629,9 @@ int drm_dev_init(struct drm_device *dev,
>  	dev->dev = get_device(parent);
>  	dev->driver = driver;
>  
> +	INIT_LIST_HEAD(&dev->managed.resources);
> +	spin_lock_init(&dev->managed.lock);
> +
>  	/* no per-device feature limits by default */
>  	dev->driver_features = ~0u;
>  
> @@ -828,8 +831,17 @@ static void drm_dev_release(struct kref *ref)
>  		dev->driver->release(dev);
>  	} else {
>  		drm_dev_fini(dev);
> +	}
> +
> +	drm_managed_release(dev);
> +
> +	if (!dev->driver->release && !dev->managed.final_kfree) {
> +		WARN_ON(!list_empty(&dev->managed.resources));
>  		kfree(dev);
>  	}
> +
> +	if (dev->managed.final_kfree)
> +		kfree(dev->managed.final_kfree);
>  }
>  
>  /**
> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> index aeec2e68d772..8c2628dfc6c7 100644
> --- a/drivers/gpu/drm/drm_internal.h
> +++ b/drivers/gpu/drm/drm_internal.h
> @@ -89,6 +89,9 @@ void drm_prime_remove_buf_handle_locked(struct drm_prime_file_private *prime_fpr
>  struct drm_minor *drm_minor_acquire(unsigned int minor_id);
>  void drm_minor_release(struct drm_minor *minor);
>  
> +/* drm_managed.c */
> +void drm_managed_release(struct drm_device *dev);
> +
>  /* drm_vblank.c */
>  void drm_vblank_disable_and_save(struct drm_device *dev, unsigned int pipe);
>  void drm_vblank_cleanup(struct drm_device *dev);
> diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> new file mode 100644
> index 000000000000..57dc79fa90af
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_managed.c
> @@ -0,0 +1,186 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2020 Intel
> + *
> + * Based on drivers/base/devres.c
> + */
> +
> +#include <drm/drm_managed.h>
> +
> +#include <linux/list.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +
> +#include <drm/drm_device.h>
> +#include <drm/drm_print.h>
> +
> +/**
> + * DOC: managed resources
> + *
> + * Inspired by struct &device managed resources, but tied to the lifetime of
> + * struct &drm_device, which can outlive the underlying physical device, usually
> + * when userspace has some open files and other handles to resources still open.
> + */
> +struct drmres_node {
> +	struct list_head	entry;
> +	drmres_release_t	release;
> +	const char		*name;
> +	size_t			size;
> +};

At a later point, we could have debugfs for instances of this data
structure. There's already a name field.

> +
> +struct drmres {
> +	struct drmres_node		node;
> +	/*
> +	 * Some archs want to perform DMA into kmalloc caches
> +	 * and need a guaranteed alignment larger than
> +	 * the alignment of a 64-bit integer.
> +	 * Thus we use ARCH_KMALLOC_MINALIGN here and get exactly the same
> +	 * buffer alignment as if it was allocated by plain kmalloc().
> +	 */
> +	u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];
> +};
> +
> +void drm_managed_release(struct drm_device *dev)
> +{
> +	struct drmres *dr, *tmp;
> +
> +	drm_dbg_drmres(dev, "drmres release begin\n");
> +	list_for_each_entry_safe(dr, tmp, &dev->managed.resources, node.entry) {
> +		drm_dbg_drmres(dev, "REL %p %s (%zu bytes)\n",
> +			       dr, dr->node.name, dr->node.size);
> +
> +		if (dr->node.release)
> +			dr->node.release(dev, dr->node.size ? *(void **)&dr->data : NULL);
> +
> +		list_del(&dr->node.entry);
> +		kfree(dr);
> +	}
> +	drm_dbg_drmres(dev, "drmres release end\n");
> +}
> +
> +/*
> + * Always inline so that kmallc_track_caller tracks the actual interesting

'kmalloc_node_track_caller'

> + * caller outside of drm_managed.c.
> + */
> +static __always_inline struct drmres * alloc_dr(drmres_release_t release,
> +						size_t size, gfp_t gfp, int nid)
> +{
> +	size_t tot_size;
> +	struct drmres *dr;
> +
> +	/* We must catch any near-SIZE_MAX cases that could overflow. */
> +	if (unlikely(check_add_overflow(sizeof(*dr), size, &tot_size)))
> +		return NULL;
> +
> +	dr = kmalloc_node_track_caller(tot_size, gfp, nid);
> +	if (unlikely(!dr))
> +		return NULL;
> +
> +	memset(dr, 0, offsetof(struct drmres, data));
> +
> +	INIT_LIST_HEAD(&dr->node.entry);
> +	dr->node.release = release;
> +	dr->node.size = size;
> +
> +	return dr;
> +}
> +
> +static void del_dr(struct drm_device *dev, struct drmres *dr)
> +{
> +	list_del_init(&dr->node.entry);
> +
> +	drm_dbg_drmres(dev, "DEL %p %s (%lu bytes)\n",
> +		       dr, dr->node.name, (unsigned long) dr->node.size);
> +}
> +
> +static void add_dr(struct drm_device *dev, struct drmres *dr)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&dev->managed.lock, flags);
> +	list_add(&dr->node.entry, &dev->managed.resources);
> +	spin_unlock_irqrestore(&dev->managed.lock, flags);
> +
> +	drm_dbg_drmres(dev, "ADD %p %s (%lu bytes)\n",
> +		       dr, dr->node.name, (unsigned long) dr->node.size);

If the insert code blows up, it might be helpful to have this message in
the log already. So should this message be located before the code for
inserting the entry?

> +}
> +
> +void drmm_add_final_kfree(struct drm_device *dev, void *parent)

Can you come up with better names? 'final_kfree' sounds like a function
pointer to an implementation of kfree() and 'parent' sounds like the
parent device in a device hierarchy.

I suggest to rename 'parent' to 'container' and 'final_kfree'
'drmm_container'. The function's name could be drmm_dev_set_container().

> +{
> +	WARN_ON(dev->managed.final_kfree);
> +	WARN_ON(dev < (struct drm_device *) parent);
> +	WARN_ON(dev + 1 >= (struct drm_device *) (parent + ksize(parent)));
> +	dev->managed.final_kfree = parent;
> +}
> +EXPORT_SYMBOL(drmm_add_final_kfree);
> +
> +int __drmm_add_action(struct drm_device *dev,
> +		      drmres_release_t action,
> +		      void *data, const char *name)

Is there a reason to pass in 'void* data' instead of 'void** datap'? The
latter would communicate what this parameter is for and not need void_ptr.

In any case, there seems to be no interface to remove an added action
(e.g., __drmm_remove_action()). Please see my comment on drmm_kfree() below.

And more generally, do we really need __drmm_add_action() in it's
current form? I'd change it to __drmm_kmalloc(), which is drmm_kmalloc()
plus optional release-action and name parameters. And drm_kmalloc()
would be a simple wrapper in the header file, just like drmm_kcalloc().

> +{
> +	struct drmres *dr;
> +	void **void_ptr;
> +
> +	dr = alloc_dr(action, data ? sizeof(void*) : 0,
> +		      GFP_KERNEL | __GFP_ZERO,
> +		      dev_to_node(dev->dev));
> +	if (!dr) {
> +		drm_dbg_drmres(dev, "failed to add action %s for %p\n",
> +			       name, data);
> +		return -ENOMEM;
> +	}
> +
> +	dr->node.name = name;
> +	if (data) {
> +		void_ptr = (void **)&dr->data;
> +		*void_ptr = data;
> +	}
> +
> +	add_dr(dev, dr);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(__drmm_add_action);
> +
> +void *drmm_kmalloc(struct drm_device *dev, size_t size, gfp_t gfp)
> +{
> +	struct drmres *dr;
> +
> +	dr = alloc_dr(NULL, size, gfp, dev_to_node(dev->dev));
> +	if (!dr) {
> +		drm_dbg_drmres(dev, "failed to allocate %zu bytes, %u flags\n",
> +			       size, gfp);
> +		return NULL;
> +	}
> +	dr->node.name = "kmalloc";
> +
> +	add_dr(dev, dr);
> +
> +	return dr->data;
> +}
> +EXPORT_SYMBOL(drmm_kmalloc);
> +
> +void drmm_kfree(struct drm_device *dev, void *data)

I suggest to wrap this function around an implementatian that calls the
optional release action. drmm_kfree() would become a trivial wrapper in
the header file.

Best regards
Thomas

> +{
> +	struct drmres *dr_match = NULL, *dr;
> +	unsigned long flags;
> +
> +	if (!data)
> +		return;
> +
> +	spin_lock_irqsave(&dev->managed.lock, flags);
> +	list_for_each_entry(dr, &dev->managed.resources, node.entry) {
> +		if (dr->data == data) {
> +			dr_match = dr;
> +			del_dr(dev, dr_match);
> +			break;
> +		}
> +	}
> +	spin_unlock_irqrestore(&dev->managed.lock, flags);
> +
> +	if (WARN_ON(!dr_match))
> +		return;
> +
> +	kfree(dr_match);
> +}
> +EXPORT_SYMBOL(drmm_kfree);
> diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
> index bb60a949f416..d39132b477dd 100644
> --- a/include/drm/drm_device.h
> +++ b/include/drm/drm_device.h
> @@ -67,6 +67,21 @@ struct drm_device {
>  	/** @dev: Device structure of bus-device */
>  	struct device *dev;
>  
> +	/**
> +	 * @managed:
> +	 *
> +	 * Managed resources linked to the lifetime of this &drm_device as
> +	 * tracked by @ref.
> +	 */
> +	struct {
> +		/** @managed.resources: managed resources list */
> +		struct list_head resources;
> +		/** @managed.final_kfree: pointer for final kfree() call */
> +		void *final_kfree;
> +		/** @managed.lock: protects @managed.resources */
> +		spinlock_t lock;
> +	} managed;
> +
>  	/** @driver: DRM driver managing the device */
>  	struct drm_driver *driver;
>  
> diff --git a/include/drm/drm_managed.h b/include/drm/drm_managed.h
> new file mode 100644
> index 000000000000..7b5df7d09b19
> --- /dev/null
> +++ b/include/drm/drm_managed.h
> @@ -0,0 +1,30 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#ifndef _DRM_MANAGED_H_
> +#define _DRM_MANAGED_H_
> +
> +#include <linux/gfp.h>
> +#include <linux/types.h>
> +
> +struct drm_device;
> +
> +typedef void (*drmres_release_t)(struct drm_device *dev, void *res);
> +
> +#define drmm_add_action(dev, action, data) \
> +	__drmm_add_action(dev, action, data, #action)
> +
> +int __must_check __drmm_add_action(struct drm_device *dev,
> +				   drmres_release_t action,
> +				   void *data, const char *name);
> +
> +void drmm_add_final_kfree(struct drm_device *dev, void *parent);
> +
> +void *drmm_kmalloc(struct drm_device *dev, size_t size, gfp_t gfp) __malloc;
> +static inline void *drmm_kzalloc(struct drm_device *dev, size_t size, gfp_t gfp)
> +{
> +	return drmm_kmalloc(dev, size, gfp | __GFP_ZERO);
> +}
> +
> +void drmm_kfree(struct drm_device *dev, void *data);
> +
> +#endif
> diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
> index ca7cee8e728a..1c9417430d08 100644
> --- a/include/drm/drm_print.h
> +++ b/include/drm/drm_print.h
> @@ -313,6 +313,10 @@ enum drm_debug_category {
>  	 * @DRM_UT_DP: Used in the DP code.
>  	 */
>  	DRM_UT_DP		= 0x100,
> +	/**
> +	 * @DRM_UT_DRMRES: Used in the drm managed resources code.
> +	 */
> +	DRM_UT_DRMRES		= 0x200,
>  };
>  
>  static inline bool drm_debug_enabled(enum drm_debug_category category)
> @@ -442,6 +446,8 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
>  	drm_dev_dbg((drm)->dev, DRM_UT_LEASE, fmt, ##__VA_ARGS__)
>  #define drm_dbg_dp(drm, fmt, ...)					\
>  	drm_dev_dbg((drm)->dev, DRM_UT_DP, fmt, ##__VA_ARGS__)
> +#define drm_dbg_drmres(drm, fmt, ...)					\
> +	drm_dev_dbg((drm)->dev, DRM_UT_DRMRES, fmt, ##__VA_ARGS__)
>  
>  
>  /*
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer