hvc_console change results in corrupt oops output

Tabi Timur-B04825 B04825 at freescale.com
Tue Jul 5 23:51:09 EST 2011

Benjamin Herrenschmidt wrote:

> That is a fun conclusion considering that hvc has been written for the
> pseries hypervisor which ... can return BUSY on writes :-)

Go read the original thread.  The problem is that tty writes and console 
writes are treated the same by the hvc client driver.  If a client driver 
detects that the hypervisor is busy, it has the choice of either spinning 
or returning right away.  Spinning is not acceptable for tty output, so 
all drivers return right away.  hvc then drops the unwritten characters.

According to Hendrik, this is still happening.

> We just need to fix HVC properly.

Where were you two years ago?  I complained about the problem, and even 
posted a hackish "fix".  The response I got was tepid -- some 
acknowledgement that the problem exists, but no real desire to fix it by 

So I had no choice but to abandon hvc.  And frankly, I still don't 
understand why it exists.  Since then, I wrote a very nice console/tty 
driver, and I have no plans to return to hvc even if the problem is fixed.

Timur Tabi
Linux kernel developer at Freescale

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