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Subject[PATCH] fbmem: fix race condition between register_framebuffer() and fb_open()
Date
register_framebuffer() acquires registration_lock, then calls
do_register_framebuffer() which calls fb_notifier_call_chain()
which calls fb_open() which calls get_fb_info() which tries
(at last) to acquire registration_lock again.
This is a workaround.

Signed-off-by: Fabio Erculiani <lxnay@sabayon.org>
---
drivers/video/fbmem.c | 13 ++++++++++++-
1 files changed, 12 insertions(+), 1 deletions(-)
diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index 5aac00e..b9831a0 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1628,6 +1628,11 @@ static int do_register_framebuffer(struct fb_info *fb_info)
event.info = fb_info;
if (!lock_fb_info(fb_info))
return -ENODEV;
+
+ /* FIXME: unlock registration mutex before registration
+ * notification is sent, in order to avoid deadlock.
+ */
+ mutex_unlock(&registration_lock);
fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
unlock_fb_info(fb_info);
return 0;
@@ -1692,7 +1697,13 @@ register_framebuffer(struct fb_info *fb_info)

mutex_lock(&registration_lock);
ret = do_register_framebuffer(fb_info);
- mutex_unlock(&registration_lock);
+ if (ret != 0)
+ /*
+ * FIXME: mutex is unlocked only if ret == 0.
+ * This is the second part of the workaround
+ * that prevents deadlocking.
+ */
+ mutex_unlock(&registration_lock);

return ret;
}
--
1.7.5.rc1


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