Hi,

Since nobody wants to burn his fingers and touch the tty subsystem,
I've committed this fix as a bandaid to CURRENT and will MCF it after
a week. More work is needed to properly lock and protect the tty subsystem
of course.

During two month of testing this patch stopped the frequent panics we got on
our SMP systems.

I'm willing to do the tty locking changes if someone helps
me to do it and reviews the changes.

--
Martin

On Sun, 10 Sep 2006, Martin Blapp wrote:

mbr         2006-09-10 16:51:56 UTC

 FreeBSD src repository

 Modified files:
   sys/kern             tty.c
 Log:
 Fix locking race in ttymodem(). The locking of the proctree happens too late
 and opens a small race window before tp->t_session->s_leader is accessed. In 
case
 tp->t_session has just been set to NULL elsewhere, we get a panic().

 This fix is a bandaid until someone else fixes the whole locking in the tty 
subsystem.
 Definitly more work needs to be done.

 MFC after:      1 week
 Reviewed by:    mlaier
 PR:             kern/103101

 Revision  Changes    Path
 1.258     +2 -2      src/sys/kern/tty.c

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