2008-11-03 07:07:11

by Keith Packard

Subject: [PATCH] [drivers/video/fb] Eliminate recursive mutex in compat fb ioctl path

fb_compat_ioctl grabbed the fb mutex and then called fb_ioctl, which also
grabs the same mutex. I traced through all existing fb_compat_ioctl
functions in the various fb drivers and found that they also transform their
arguments and call the native fb_ioctl function. So, it is correct to just
remove the mutex_lock/mutex_unlock pair in the top-level compat path.

Signed-off-by: Keith Packard <[email protected]>
---
drivers/video/fbmem.c | 2 --
1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index cd5f20d..548cf26 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1253,7 +1253,6 @@ fb_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
struct fb_ops *fb = info->fbops;
long ret = -ENOIOCTLCMD;

- mutex_lock(&info->lock);
switch(cmd) {
case FBIOGET_VSCREENINFO:
case FBIOPUT_VSCREENINFO:
@@ -1279,7 +1278,6 @@ fb_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
ret = fb->fb_compat_ioctl(info, cmd, arg);
break;
}
- mutex_unlock(&info->lock);
return ret;
}
#endif
--
1.5.6.5

2008-11-03 10:12:38

by Geert Uytterhoeven

Subject: Re: [PATCH] [drivers/video/fb] Eliminate recursive mutex in compat fb ioctl path

On Sun, 2 Nov 2008, Keith Packard wrote:
> fb_compat_ioctl grabbed the fb mutex and then called fb_ioctl, which also
> grabs the same mutex. I traced through all existing fb_compat_ioctl
> functions in the various fb drivers and found that they also transform their
> arguments and call the native fb_ioctl function. So, it is correct to just
> remove the mutex_lock/mutex_unlock pair in the top-level compat path.

Last week I submitted an alternative fix: http://lkml.org/lkml/2008/10/31/162

Probably Rafael wants to keep track of this regression, too?

> Signed-off-by: Keith Packard <[email protected]>
> ---
> drivers/video/fbmem.c | 2 --
> 1 files changed, 0 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index cd5f20d..548cf26 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1253,7 +1253,6 @@ fb_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> struct fb_ops *fb = info->fbops;
> long ret = -ENOIOCTLCMD;
>
> - mutex_lock(&info->lock);
> switch(cmd) {
> case FBIOGET_VSCREENINFO:
> case FBIOPUT_VSCREENINFO:
> @@ -1279,7 +1278,6 @@ fb_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> ret = fb->fb_compat_ioctl(info, cmd, arg);
> break;
> }
> - mutex_unlock(&info->lock);
> return ret;
> }
> #endif

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
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