[ resend since dri-devel wasn't Cc'ed on all patches, sorry for the noise ]
Hello,
The patches in this series are mostly changes suggested by Daniel Vetter
to fix some race conditions that exists between the fbdev core (fbmem)
and sysfb with regard to device registration and removal.
For example, it is currently possible for sysfb to register a platform
device after a real DRM driver was registered and requested to remove the
conflicting framebuffers.
A symptom of this issue, was worked around with by commit fb561bf9abde
("fbdev: Prevent probing generic drivers if a FB is already registered")
but that's really a hack and should be reverted.
This series attempt to fix it more properly and reverted the mentioned
hack. This will also unblock a pending patch to not make num_registered_fb
visible to drivers anymore, since that's really internal to fbdev core.
Patch #1 is just a trivial preparatory change.
Patch #2 add sysfb_disable() and sysfb_try_unregister() helpers for fbmem
to use them.
Patch #3 changes how is dealt with conflicting framebuffers unregistering,
rather than having a variable to determine if a lock should be take, it
just drops the lock before unregistering the platform device.
Patch #4 fixes the mentioned race conditions and finally patch #5 is the
revert patch that was posted by Daniel before but he dropped from his set.
The patches were tested on a rpi4 using different video configurations:
(simpledrm -> vc4 both builtin, only vc4 builtin, only simpledrm builtin
and simpledrm builtin with vc4 built as a module).
I'm sending as an RFC since there are many changes to the locking scheme
and that is always tricky to get right. Please let me know what you think.
Best regards,
Javier
Daniel Vetter (1):
Revert "fbdev: Prevent probing generic drivers if a FB is already
registered"
Javier Martinez Canillas (4):
firmware: sysfb: Make sysfb_create_simplefb() return a pdev pointer
firmware: sysfb: Add helpers to unregister a pdev and disable
registration
fbdev: Restart conflicting fb removal loop when unregistering devices
fbdev: Fix some race conditions between fbmem and sysfb
drivers/firmware/sysfb.c | 51 ++++++++++++++++++++++++++-----
drivers/firmware/sysfb_simplefb.c | 24 +++++++++------
drivers/video/fbdev/core/fbmem.c | 38 ++++++++++++++++++-----
drivers/video/fbdev/efifb.c | 11 -------
drivers/video/fbdev/simplefb.c | 11 -------
include/linux/fb.h | 1 -
include/linux/sysfb.h | 29 +++++++++++++++---
7 files changed, 112 insertions(+), 53 deletions(-)
--
2.35.1
This function just returned 0 on success or an errno code on error, but it
could be useful to sysfb_init() to get a pointer to the device registered.
Signed-off-by: Javier Martinez Canillas <[email protected]>
---
drivers/firmware/sysfb.c | 4 ++--
drivers/firmware/sysfb_simplefb.c | 24 +++++++++++++++---------
include/linux/sysfb.h | 10 +++++-----
3 files changed, 22 insertions(+), 16 deletions(-)
diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
index 2bfbb05f7d89..b032f40a92de 100644
--- a/drivers/firmware/sysfb.c
+++ b/drivers/firmware/sysfb.c
@@ -46,8 +46,8 @@ static __init int sysfb_init(void)
/* try to create a simple-framebuffer device */
compatible = sysfb_parse_mode(si, &mode);
if (compatible) {
- ret = sysfb_create_simplefb(si, &mode);
- if (!ret)
+ pd = sysfb_create_simplefb(si, &mode);
+ if (!IS_ERR(pd))
return 0;
}
diff --git a/drivers/firmware/sysfb_simplefb.c b/drivers/firmware/sysfb_simplefb.c
index 76c4abc42a30..c42648ed3aad 100644
--- a/drivers/firmware/sysfb_simplefb.c
+++ b/drivers/firmware/sysfb_simplefb.c
@@ -57,8 +57,8 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
return false;
}
-__init int sysfb_create_simplefb(const struct screen_info *si,
- const struct simplefb_platform_data *mode)
+__init struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
+ const struct simplefb_platform_data *mode)
{
struct platform_device *pd;
struct resource res;
@@ -76,7 +76,7 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
base |= (u64)si->ext_lfb_base << 32;
if (!base || (u64)(resource_size_t)base != base) {
printk(KERN_DEBUG "sysfb: inaccessible VRAM base\n");
- return -EINVAL;
+ return ERR_PTR(-EINVAL);
}
/*
@@ -93,7 +93,7 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
length = mode->height * mode->stride;
if (length > size) {
printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
- return -EINVAL;
+ return ERR_PTR(-EINVAL);
}
length = PAGE_ALIGN(length);
@@ -104,25 +104,31 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
res.start = base;
res.end = res.start + length - 1;
if (res.end <= res.start)
- return -EINVAL;
+ return ERR_PTR(-EINVAL);
pd = platform_device_alloc("simple-framebuffer", 0);
if (!pd)
- return -ENOMEM;
+ return ERR_PTR(-ENOMEM);
sysfb_apply_efi_quirks(pd);
ret = platform_device_add_resources(pd, &res, 1);
if (ret) {
platform_device_put(pd);
- return ret;
+ return ERR_PTR(ret);
}
ret = platform_device_add_data(pd, mode, sizeof(*mode));
if (ret) {
platform_device_put(pd);
- return ret;
+ return ERR_PTR(ret);
}
- return platform_device_add(pd);
+ ret = platform_device_add(pd);
+ if (ret) {
+ platform_device_put(pd);
+ return ERR_PTR(ret);
+ }
+
+ return pd;
}
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
index b0dcfa26d07b..708152e9037b 100644
--- a/include/linux/sysfb.h
+++ b/include/linux/sysfb.h
@@ -72,8 +72,8 @@ static inline void sysfb_apply_efi_quirks(struct platform_device *pd)
bool sysfb_parse_mode(const struct screen_info *si,
struct simplefb_platform_data *mode);
-int sysfb_create_simplefb(const struct screen_info *si,
- const struct simplefb_platform_data *mode);
+struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
+ const struct simplefb_platform_data *mode);
#else /* CONFIG_SYSFB_SIMPLE */
@@ -83,10 +83,10 @@ static inline bool sysfb_parse_mode(const struct screen_info *si,
return false;
}
-static inline int sysfb_create_simplefb(const struct screen_info *si,
- const struct simplefb_platform_data *mode)
+static inline struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
+ const struct simplefb_platform_data *mode)
{
- return -EINVAL;
+ return ERR_PTR(-EINVAL);
}
#endif /* CONFIG_SYSFB_SIMPLE */
--
2.35.1
These can be used by subsystems to unregister a platform device registered
by sysfb and also to disable future platform device registration in sysfb.
Suggested-by: Daniel Vetter <[email protected]>
Signed-off-by: Javier Martinez Canillas <[email protected]>
---
drivers/firmware/sysfb.c | 47 +++++++++++++++++++++++++++++++++++-----
include/linux/sysfb.h | 19 ++++++++++++++++
2 files changed, 60 insertions(+), 6 deletions(-)
diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
index b032f40a92de..08ae78c083f1 100644
--- a/drivers/firmware/sysfb.c
+++ b/drivers/firmware/sysfb.c
@@ -34,21 +34,52 @@
#include <linux/screen_info.h>
#include <linux/sysfb.h>
+static struct platform_device *pd;
+static DEFINE_MUTEX(load_lock);
+static bool disabled;
+
+void sysfb_disable(void)
+{
+ mutex_lock(&load_lock);
+ disabled = true;
+ mutex_unlock(&load_lock);
+}
+EXPORT_SYMBOL_GPL(sysfb_disable);
+
+bool sysfb_try_unregister(struct device *dev)
+{
+ bool ret = true;
+
+ mutex_lock(&load_lock);
+ if (!pd || pd != to_platform_device(dev))
+ return false;
+
+ platform_device_unregister(to_platform_device(dev));
+ pd = NULL;
+ mutex_unlock(&load_lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(sysfb_try_unregister);
+
static __init int sysfb_init(void)
{
struct screen_info *si = &screen_info;
struct simplefb_platform_data mode;
- struct platform_device *pd;
const char *name;
bool compatible;
- int ret;
+ int ret = 0;
+
+ mutex_lock(&load_lock);
+ if (disabled)
+ goto unlock_mutex;
/* try to create a simple-framebuffer device */
compatible = sysfb_parse_mode(si, &mode);
if (compatible) {
pd = sysfb_create_simplefb(si, &mode);
if (!IS_ERR(pd))
- return 0;
+ goto unlock_mutex;
}
/* if the FB is incompatible, create a legacy framebuffer device */
@@ -60,8 +91,10 @@ static __init int sysfb_init(void)
name = "platform-framebuffer";
pd = platform_device_alloc(name, 0);
- if (!pd)
- return -ENOMEM;
+ if (!pd) {
+ ret = -ENOMEM;
+ goto unlock_mutex;
+ }
sysfb_apply_efi_quirks(pd);
@@ -73,9 +106,11 @@ static __init int sysfb_init(void)
if (ret)
goto err;
- return 0;
+ goto unlock_mutex;
err:
platform_device_put(pd);
+unlock_mutex:
+ mutex_unlock(&load_lock);
return ret;
}
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
index 708152e9037b..e8c0313fac8f 100644
--- a/include/linux/sysfb.h
+++ b/include/linux/sysfb.h
@@ -55,6 +55,25 @@ struct efifb_dmi_info {
int flags;
};
+#ifdef CONFIG_SYSFB
+
+void sysfb_disable(void);
+bool sysfb_try_unregister(struct device *dev);
+
+#else /* CONFIG_SYSFB */
+
+static inline void sysfb_disable(void)
+{
+
+}
+
+static inline bool sysfb_try_unregister(struct device *dev)
+{
+ return false;
+}
+
+#endif /* CONFIG_SYSFB */
+
#ifdef CONFIG_EFI
extern struct efifb_dmi_info efifb_dmi_list[];
--
2.35.1
From: Daniel Vetter <[email protected]>
This reverts commit fb561bf9abde49f7e00fdbf9ed2ccf2d86cac8ee.
With
commit 27599aacbaefcbf2af7b06b0029459bbf682000d
Author: Thomas Zimmermann <[email protected]>
Date: Tue Jan 25 10:12:18 2022 +0100
fbdev: Hot-unplug firmware fb devices on forced removal
this should be fixed properly and we can remove this somewhat hackish
check here (e.g. this won't catch drm drivers if fbdev emulation isn't
enabled).
Cc: Thomas Zimmermann <[email protected]>
Cc: Zack Rusin <[email protected]>
Cc: Javier Martinez Canillas <[email protected]>
Cc: Zack Rusin <[email protected]>
Cc: Hans de Goede <[email protected]>
Cc: Ilya Trukhanov <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Cc: Peter Jones <[email protected]>
Cc: [email protected]
Signed-off-by: Javier Martinez Canillas <[email protected]>
---
drivers/video/fbdev/efifb.c | 11 -----------
drivers/video/fbdev/simplefb.c | 11 -----------
2 files changed, 22 deletions(-)
diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
index ea42ba6445b2..edca3703b964 100644
--- a/drivers/video/fbdev/efifb.c
+++ b/drivers/video/fbdev/efifb.c
@@ -351,17 +351,6 @@ static int efifb_probe(struct platform_device *dev)
char *option = NULL;
efi_memory_desc_t md;
- /*
- * Generic drivers must not be registered if a framebuffer exists.
- * If a native driver was probed, the display hardware was already
- * taken and attempting to use the system framebuffer is dangerous.
- */
- if (num_registered_fb > 0) {
- dev_err(&dev->dev,
- "efifb: a framebuffer is already registered\n");
- return -EINVAL;
- }
-
if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI || pci_dev_disabled)
return -ENODEV;
diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
index 94fc9c6d0411..0ef41173325a 100644
--- a/drivers/video/fbdev/simplefb.c
+++ b/drivers/video/fbdev/simplefb.c
@@ -413,17 +413,6 @@ static int simplefb_probe(struct platform_device *pdev)
struct simplefb_par *par;
struct resource *res, *mem;
- /*
- * Generic drivers must not be registered if a framebuffer exists.
- * If a native driver was probed, the display hardware was already
- * taken and attempting to use the system framebuffer is dangerous.
- */
- if (num_registered_fb > 0) {
- dev_err(&pdev->dev,
- "simplefb: a framebuffer is already registered\n");
- return -EINVAL;
- }
-
if (fb_get_options("simplefb", NULL))
return -ENODEV;
--
2.35.1
Hello Daniel,
On 4/7/22 11:03, Daniel Vetter wrote:
> On Wed, Apr 06, 2022 at 11:39:15PM +0200, Javier Martinez Canillas wrote:
>> This function just returned 0 on success or an errno code on error, but it
>> could be useful to sysfb_init() to get a pointer to the device registered.
>>
>> Signed-off-by: Javier Martinez Canillas <[email protected]>
>
> You need to rebase this onto 202c08914ba5 ("firmware: sysfb: fix
> platform-device leak in error path") which fixes the same error path leak
> you are fixing in here too. Or we just have a neat conflict when merging
> :-) But in that case please mention that you fix the error path leak too
> so it's less confusing when Linus or someone needs to resolve the
> conflict.
>
Ups, I thought that had my local tree up-to-date but it seems that was a few
days old. I've updated my remote now and rebased, so will have this fixed in
the next revision of the series.
And this patch becomes smaller indeed :)
> Anyway Reviewed-by: Daniel Vetter <[email protected]>
>
Thanks!
--
Best regards,
Javier Martinez Canillas
Linux Engineering
Red Hat
Drivers that want to remove registered conflicting framebuffers prior to
register their own framebuffer, calls remove_conflicting_framebuffers().
This function takes the registration_lock mutex, to prevent a races when
drivers register framebuffer devices. But if a conflicting framebuffer
device is found, the underlaying platform device is unregistered and this
will lead to the platform driver .remove callback to be called, which in
turn will call to the unregister_framebuffer() that takes the same lock.
To prevent this, a struct fb_info.forced_out field was used as indication
to unregister_framebuffer() whether the mutex has to be grabbed or not.
A cleaner solution is to drop the lock before platform_device_unregister()
so unregister_framebuffer() can take it when called from the fbdev driver,
and just grab the lock again after the device has been registered and do
a removal loop restart.
Since the framebuffer devices will already be removed, the loop would just
finish when no more conflicting framebuffers are found.
Suggested-by: Daniel Vetter <[email protected]>
Signed-off-by: Javier Martinez Canillas <[email protected]>
---
drivers/video/fbdev/core/fbmem.c | 21 ++++++++++++++-------
include/linux/fb.h | 1 -
2 files changed, 14 insertions(+), 8 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index b585339509b0..c1bfb8df9cba 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1555,6 +1555,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
{
int i;
+restart_removal:
/* check all firmware fbs and kick off if the base addr overlaps */
for_each_registered_fb(i) {
struct apertures_struct *gen_aper;
@@ -1582,8 +1583,18 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
* fix would add code to remove the device from the system.
*/
if (dev_is_platform(device)) {
- registered_fb[i]->forced_out = true;
+ /*
+ * Drop the lock since the driver will call to the
+ * unregister_framebuffer() function that takes it.
+ */
+ mutex_unlock(®istration_lock);
platform_device_unregister(to_platform_device(device));
+ mutex_lock(®istration_lock);
+ /*
+ * Restart the removal now that the platform device
+ * has been unregistered and its associated fb gone.
+ */
+ goto restart_removal;
} else {
pr_warn("fb%d: cannot remove device\n", i);
do_unregister_framebuffer(registered_fb[i]);
@@ -1917,13 +1928,9 @@ EXPORT_SYMBOL(register_framebuffer);
void
unregister_framebuffer(struct fb_info *fb_info)
{
- bool forced_out = fb_info->forced_out;
-
- if (!forced_out)
- mutex_lock(®istration_lock);
+ mutex_lock(®istration_lock);
do_unregister_framebuffer(fb_info);
- if (!forced_out)
- mutex_unlock(®istration_lock);
+ mutex_unlock(®istration_lock);
}
EXPORT_SYMBOL(unregister_framebuffer);
diff --git a/include/linux/fb.h b/include/linux/fb.h
index 39baa9a70779..f1e0cd751b06 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -503,7 +503,6 @@ struct fb_info {
} *apertures;
bool skip_vt_switch; /* no VT switch on suspend/resume required */
- bool forced_out; /* set when being removed by another driver */
};
static inline struct apertures_struct *alloc_apertures(unsigned int max_num) {
--
2.35.1
On 4/7/22 11:06, Daniel Vetter wrote:
> On Wed, Apr 06, 2022 at 11:39:16PM +0200, Javier Martinez Canillas wrote:
[snip]
>> +}
>> +EXPORT_SYMBOL_GPL(sysfb_try_unregister);
>
> Kerneldoc for these plus adding that to
> Documentation/firmware/other_interfaces.rst would be really neat.
>
> With that added Reviewed-by: Daniel Vetter <[email protected]>
>
>
I will, thanks for pointing this out.
--
Best regards,
Javier Martinez Canillas
Linux Engineering
Red Hat
On Wed, Apr 06, 2022 at 11:39:15PM +0200, Javier Martinez Canillas wrote:
> This function just returned 0 on success or an errno code on error, but it
> could be useful to sysfb_init() to get a pointer to the device registered.
>
> Signed-off-by: Javier Martinez Canillas <[email protected]>
You need to rebase this onto 202c08914ba5 ("firmware: sysfb: fix
platform-device leak in error path") which fixes the same error path leak
you are fixing in here too. Or we just have a neat conflict when merging
:-) But in that case please mention that you fix the error path leak too
so it's less confusing when Linus or someone needs to resolve the
conflict.
Anyway Reviewed-by: Daniel Vetter <[email protected]>
> ---
>
> drivers/firmware/sysfb.c | 4 ++--
> drivers/firmware/sysfb_simplefb.c | 24 +++++++++++++++---------
> include/linux/sysfb.h | 10 +++++-----
> 3 files changed, 22 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
> index 2bfbb05f7d89..b032f40a92de 100644
> --- a/drivers/firmware/sysfb.c
> +++ b/drivers/firmware/sysfb.c
> @@ -46,8 +46,8 @@ static __init int sysfb_init(void)
> /* try to create a simple-framebuffer device */
> compatible = sysfb_parse_mode(si, &mode);
> if (compatible) {
> - ret = sysfb_create_simplefb(si, &mode);
> - if (!ret)
> + pd = sysfb_create_simplefb(si, &mode);
> + if (!IS_ERR(pd))
> return 0;
> }
>
> diff --git a/drivers/firmware/sysfb_simplefb.c b/drivers/firmware/sysfb_simplefb.c
> index 76c4abc42a30..c42648ed3aad 100644
> --- a/drivers/firmware/sysfb_simplefb.c
> +++ b/drivers/firmware/sysfb_simplefb.c
> @@ -57,8 +57,8 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
> return false;
> }
>
> -__init int sysfb_create_simplefb(const struct screen_info *si,
> - const struct simplefb_platform_data *mode)
> +__init struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
> + const struct simplefb_platform_data *mode)
> {
> struct platform_device *pd;
> struct resource res;
> @@ -76,7 +76,7 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
> base |= (u64)si->ext_lfb_base << 32;
> if (!base || (u64)(resource_size_t)base != base) {
> printk(KERN_DEBUG "sysfb: inaccessible VRAM base\n");
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> /*
> @@ -93,7 +93,7 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
> length = mode->height * mode->stride;
> if (length > size) {
> printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
> length = PAGE_ALIGN(length);
>
> @@ -104,25 +104,31 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
> res.start = base;
> res.end = res.start + length - 1;
> if (res.end <= res.start)
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
>
> pd = platform_device_alloc("simple-framebuffer", 0);
> if (!pd)
> - return -ENOMEM;
> + return ERR_PTR(-ENOMEM);
>
> sysfb_apply_efi_quirks(pd);
>
> ret = platform_device_add_resources(pd, &res, 1);
> if (ret) {
> platform_device_put(pd);
> - return ret;
> + return ERR_PTR(ret);
> }
>
> ret = platform_device_add_data(pd, mode, sizeof(*mode));
> if (ret) {
> platform_device_put(pd);
> - return ret;
> + return ERR_PTR(ret);
> }
>
> - return platform_device_add(pd);
> + ret = platform_device_add(pd);
> + if (ret) {
> + platform_device_put(pd);
> + return ERR_PTR(ret);
> + }
> +
> + return pd;
> }
> diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
> index b0dcfa26d07b..708152e9037b 100644
> --- a/include/linux/sysfb.h
> +++ b/include/linux/sysfb.h
> @@ -72,8 +72,8 @@ static inline void sysfb_apply_efi_quirks(struct platform_device *pd)
>
> bool sysfb_parse_mode(const struct screen_info *si,
> struct simplefb_platform_data *mode);
> -int sysfb_create_simplefb(const struct screen_info *si,
> - const struct simplefb_platform_data *mode);
> +struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
> + const struct simplefb_platform_data *mode);
>
> #else /* CONFIG_SYSFB_SIMPLE */
>
> @@ -83,10 +83,10 @@ static inline bool sysfb_parse_mode(const struct screen_info *si,
> return false;
> }
>
> -static inline int sysfb_create_simplefb(const struct screen_info *si,
> - const struct simplefb_platform_data *mode)
> +static inline struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
> + const struct simplefb_platform_data *mode)
> {
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> #endif /* CONFIG_SYSFB_SIMPLE */
> --
> 2.35.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
On Wed, Apr 06, 2022 at 11:39:16PM +0200, Javier Martinez Canillas wrote:
> These can be used by subsystems to unregister a platform device registered
> by sysfb and also to disable future platform device registration in sysfb.
>
> Suggested-by: Daniel Vetter <[email protected]>
> Signed-off-by: Javier Martinez Canillas <[email protected]>
> ---
>
> drivers/firmware/sysfb.c | 47 +++++++++++++++++++++++++++++++++++-----
> include/linux/sysfb.h | 19 ++++++++++++++++
> 2 files changed, 60 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
> index b032f40a92de..08ae78c083f1 100644
> --- a/drivers/firmware/sysfb.c
> +++ b/drivers/firmware/sysfb.c
> @@ -34,21 +34,52 @@
> #include <linux/screen_info.h>
> #include <linux/sysfb.h>
>
> +static struct platform_device *pd;
> +static DEFINE_MUTEX(load_lock);
> +static bool disabled;
> +
> +void sysfb_disable(void)
> +{
> + mutex_lock(&load_lock);
> + disabled = true;
> + mutex_unlock(&load_lock);
> +}
> +EXPORT_SYMBOL_GPL(sysfb_disable);
> +
> +bool sysfb_try_unregister(struct device *dev)
> +{
> + bool ret = true;
> +
> + mutex_lock(&load_lock);
> + if (!pd || pd != to_platform_device(dev))
> + return false;
> +
> + platform_device_unregister(to_platform_device(dev));
> + pd = NULL;
> + mutex_unlock(&load_lock);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(sysfb_try_unregister);
Kerneldoc for these plus adding that to
Documentation/firmware/other_interfaces.rst would be really neat.
With that added Reviewed-by: Daniel Vetter <[email protected]>
> +
> static __init int sysfb_init(void)
> {
> struct screen_info *si = &screen_info;
> struct simplefb_platform_data mode;
> - struct platform_device *pd;
> const char *name;
> bool compatible;
> - int ret;
> + int ret = 0;
> +
> + mutex_lock(&load_lock);
> + if (disabled)
> + goto unlock_mutex;
>
> /* try to create a simple-framebuffer device */
> compatible = sysfb_parse_mode(si, &mode);
> if (compatible) {
> pd = sysfb_create_simplefb(si, &mode);
> if (!IS_ERR(pd))
> - return 0;
> + goto unlock_mutex;
> }
>
> /* if the FB is incompatible, create a legacy framebuffer device */
> @@ -60,8 +91,10 @@ static __init int sysfb_init(void)
> name = "platform-framebuffer";
>
> pd = platform_device_alloc(name, 0);
> - if (!pd)
> - return -ENOMEM;
> + if (!pd) {
> + ret = -ENOMEM;
> + goto unlock_mutex;
> + }
>
> sysfb_apply_efi_quirks(pd);
>
> @@ -73,9 +106,11 @@ static __init int sysfb_init(void)
> if (ret)
> goto err;
>
> - return 0;
> + goto unlock_mutex;
> err:
> platform_device_put(pd);
> +unlock_mutex:
> + mutex_unlock(&load_lock);
> return ret;
> }
>
> diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
> index 708152e9037b..e8c0313fac8f 100644
> --- a/include/linux/sysfb.h
> +++ b/include/linux/sysfb.h
> @@ -55,6 +55,25 @@ struct efifb_dmi_info {
> int flags;
> };
>
> +#ifdef CONFIG_SYSFB
> +
> +void sysfb_disable(void);
> +bool sysfb_try_unregister(struct device *dev);
> +
> +#else /* CONFIG_SYSFB */
> +
> +static inline void sysfb_disable(void)
> +{
> +
> +}
> +
> +static inline bool sysfb_try_unregister(struct device *dev)
> +{
> + return false;
> +}
> +
> +#endif /* CONFIG_SYSFB */
> +
> #ifdef CONFIG_EFI
>
> extern struct efifb_dmi_info efifb_dmi_list[];
> --
> 2.35.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
On Wed, Apr 06, 2022 at 11:39:17PM +0200, Javier Martinez Canillas wrote:
> Drivers that want to remove registered conflicting framebuffers prior to
> register their own framebuffer, calls remove_conflicting_framebuffers().
>
> This function takes the registration_lock mutex, to prevent a races when
> drivers register framebuffer devices. But if a conflicting framebuffer
> device is found, the underlaying platform device is unregistered and this
> will lead to the platform driver .remove callback to be called, which in
> turn will call to the unregister_framebuffer() that takes the same lock.
>
> To prevent this, a struct fb_info.forced_out field was used as indication
> to unregister_framebuffer() whether the mutex has to be grabbed or not.
>
> A cleaner solution is to drop the lock before platform_device_unregister()
> so unregister_framebuffer() can take it when called from the fbdev driver,
> and just grab the lock again after the device has been registered and do
> a removal loop restart.
>
> Since the framebuffer devices will already be removed, the loop would just
> finish when no more conflicting framebuffers are found.
>
> Suggested-by: Daniel Vetter <[email protected]>
> Signed-off-by: Javier Martinez Canillas <[email protected]>
It's always entertaining with these things since they can go boom in funny
ways, but need to a least try :-) Recursive locks are just a bit too evil.
Reviewed-by: Daniel Vetter <[email protected]>
> ---
>
> drivers/video/fbdev/core/fbmem.c | 21 ++++++++++++++-------
> include/linux/fb.h | 1 -
> 2 files changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index b585339509b0..c1bfb8df9cba 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1555,6 +1555,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
> {
> int i;
>
> +restart_removal:
> /* check all firmware fbs and kick off if the base addr overlaps */
> for_each_registered_fb(i) {
> struct apertures_struct *gen_aper;
> @@ -1582,8 +1583,18 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
> * fix would add code to remove the device from the system.
> */
> if (dev_is_platform(device)) {
> - registered_fb[i]->forced_out = true;
> + /*
> + * Drop the lock since the driver will call to the
> + * unregister_framebuffer() function that takes it.
> + */
> + mutex_unlock(®istration_lock);
> platform_device_unregister(to_platform_device(device));
> + mutex_lock(®istration_lock);
> + /*
> + * Restart the removal now that the platform device
> + * has been unregistered and its associated fb gone.
> + */
> + goto restart_removal;
> } else {
> pr_warn("fb%d: cannot remove device\n", i);
> do_unregister_framebuffer(registered_fb[i]);
> @@ -1917,13 +1928,9 @@ EXPORT_SYMBOL(register_framebuffer);
> void
> unregister_framebuffer(struct fb_info *fb_info)
> {
> - bool forced_out = fb_info->forced_out;
> -
> - if (!forced_out)
> - mutex_lock(®istration_lock);
> + mutex_lock(®istration_lock);
> do_unregister_framebuffer(fb_info);
> - if (!forced_out)
> - mutex_unlock(®istration_lock);
> + mutex_unlock(®istration_lock);
> }
> EXPORT_SYMBOL(unregister_framebuffer);
>
> diff --git a/include/linux/fb.h b/include/linux/fb.h
> index 39baa9a70779..f1e0cd751b06 100644
> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -503,7 +503,6 @@ struct fb_info {
> } *apertures;
>
> bool skip_vt_switch; /* no VT switch on suspend/resume required */
> - bool forced_out; /* set when being removed by another driver */
> };
>
> static inline struct apertures_struct *alloc_apertures(unsigned int max_num) {
> --
> 2.35.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch