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| author | Daniel Vetter <daniel.vetter@ffwll.ch> | 2019-05-28 11:03:02 +0200 |
|---|---|---|
| committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2019-06-13 10:07:09 +0200 |
| commit | 94193d2aae63c49b706b1b7e535f23cfeccec93e (patch) | |
| tree | fb4bdabdea1b031129a431f47357aaefb23e8dc4 /drivers/video | |
| parent | fe2d70d6f6ff038c20705c34695bd34ac072af14 (diff) | |
| download | linux-94193d2aae63c49b706b1b7e535f23cfeccec93e.tar.bz2 | |
fbcon: Document what I learned about fbcon locking
It's not pretty.
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Yisheng Xie <ysxie@foxmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-32-daniel.vetter@ffwll.ch
Diffstat (limited to 'drivers/video')
| -rw-r--r-- | drivers/video/fbdev/core/fbcon.c | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 31d6a4e54436..b8067e07f8a8 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -88,6 +88,25 @@ # define DPRINTK(fmt, args...) #endif +/* + * FIXME: Locking + * + * - fbcon state itself is protected by the console_lock, and the code does a + * pretty good job at making sure that lock is held everywhere it's needed. + * + * - access to the registered_fb array is entirely unprotected. This should use + * proper object lifetime handling, i.e. get/put_fb_info. This also means + * switching from indices to proper pointers for fb_info everywhere. + * + * - fbcon doesn't bother with fb_lock/unlock at all. This is buggy, since it + * means concurrent access to the same fbdev from both fbcon and userspace + * will blow up. To fix this all fbcon calls from fbmem.c need to be moved out + * of fb_lock/unlock protected sections, since otherwise we'll recurse and + * deadlock eventually. Aside: Due to these deadlock issues the fbdev code in + * fbmem.c cannot use locking asserts, and there's lots of callers which get + * the rules wrong, e.g. fbsysfs.c entirely missed fb_lock/unlock calls too. + */ + enum { FBCON_LOGO_CANSHOW = -1, /* the logo can be shown */ FBCON_LOGO_DRAW = -2, /* draw the logo to a console */ |