radeonfb as module

acquire_console_sem is exported,
but release_console_sem is not

this seems like a bug for me,
as if one acquire console_sem, he should be able to relase it

svetljo

PS.
missing symbol in (IIRC) drivers/video/aty/radeon_pm.c

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@@ -566,6 +566,7 @@
 	if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 		wake_up_interruptible(&log_wait);
 }
+EXPORT_SYMBOL(release_console_sem);
 
 /** console_conditional_schedule - yield the CPU if required
  *

True that release_console_sem should be exported as well. But that lock shouldn't be in a driver. In fbcon.c yes but not the driver. My next pacth will fix that.

Hi James,
i've some related questions :-)

are you going to merge new radeonfb driver in fbdev bk tree ? is the driver in ppc bk tree newer? (i have such impression)

svetljo

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I will end up merging Ben's latest driver. A few things have to be done tho to do that (power management code). I just added that today and I will be also restoring fbset mode changing support again.

Well... please leave it the way I did it for now. There are subtle races if you don't do. In a more general manner, there are a lot of races in fbdev regarding lack of console_sem. For example, we should take it on any mode change ioctl etc...

The problem is that, except for eventual local spinlocks, the console sem is the only way to protect the low level drivers against concurrent accesses, and those _do_ need some protection or you can have accelerated printk racing against a mode change for example, etc...

It's even worse if mode change can sleep. Some updates to fbdev I'm currently working on will require the ability to sleep from the set_par() function. I would even to sleep in blank(), but that's not possible, I think, at the moment (isn't it called by a timer in the console code ?) so I'm doing something more complicated using timers.

So almost all calls to the fbdev should be done with the console sem held (even blank imho, if you can't get it using a trylock, delay it by firing the timer).

Regarding the fb_client callbacks, to avoid lock nesting, I decided the only sane way is to have the _caller_ take the console sem. That's important as those can be called from things like set_par() which will (if the above is fixed properly) be called with the console sem already held. So the act of taking the console sem should be moved up the chain as much as possible. In the case of calls issued from outside the fbdev world, like PM callbacks, the driver can only take the console sem itself to protect against concurrent set_par among others.

Now, if you want to "hide" the console sem, maybe export an fbdev_lock/ unlock API whose implementation takes the console sem... That would allow maybe to move to a per-fbdev locking in the future provided we can deal with the "printk" problem (that is deferring actual display while still letting fbcon draw into the console buffer).

Ben.