Re: [PATCH] tty races

[Jason Baron <jbaron@redhat.com>]

On Tue, 3 May 2005, Andrew Morton wrote:

> > > We want to move away from lock_kernel()-based locking.
> > > 
> > 
> > I completely agree, but unfortunately lock_kernel() is currently used 
> > extensively throughout the tty layer. 
> 
> Well no - it's being migrated over to use tty_sem.  We shouldn't start
> heading in the reverse direction.  Plus your patch reverts part of
> http://linux.bkbits.net:8080/linux-2.5/diffs/drivers/char/tty_io.c@1.156?nav=index.html|src/|src/drivers|src/drivers/char|hist/drivers/char/tty_io.c
> in ways which might be unsafe.
> 

The patch I proposed does not add any lock_kernel() based locking. The 
only locking it adds is more tty_sem based locking to cover the 
driver->open() method. I agree though that it relies on the BKL for 
correctness.

Indeed, that is precisely that patch which introduced the problems I've 
pointed out.

> > lock_kernel() is used extensively throughout the tty layer. We can 
> > re-write the locking for the layer, but I'd like to see this bug fix in 
> > 2.6.12, if that isn't done in time.
> 
> Sorry, but AFAICT all you have done is to advocate for the existing patch
> without having attempted to fix this problem with tty_sem.  Please try to
> come up with a tty_sem-based fix.
> 

The patch I proposed fixes the open vs. open race using the tty_sem. The 
open vs. close race is closed by removing locking. Less locking seems 
better to me. 

If you're still not happy, I'll wrap the close path in the tty_sem...

thanks,

-Jason


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