From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@9fans.net
Subject: Re: [9fans] 9vx fork problem
From: "Russ Cox" <rsc@swtch.com>
Date: Sun, 29 Jun 2008 22:02:22 -0400
In-Reply-To: <20080630003250.GA8819@dinah>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Message-Id: <20080630020000.4C5791E8C22@holo.morphisms.net>
Topicbox-Message-UUID: cc1a1992-ead3-11e9-9d60-3106f5b1d025

> On 9vx, iostats suicides:
>
>   term% iostats echo
>   iostats 128: suicide: sys: trap: page fault pc=0x0000b21c
>
> Apparently, after a fork, a child retains it's parent's
> pid in _tos->pid. It isn't updated until the next syscall
> finishes with kexit.
>
> This is a problem if the child's first function call is
> malloc. When malloc locks it's pool, it stores the pid
> from _tos in a private area. After the kernel returns from
> the brk, _tos->pid has been corrected by the call to kexit.
> Punlock then fails because the pids don't match.
>
> I'm not sure of the best way to go about fixing this.

Thank you for the detailed reports.
It makes it very easy to fix the bugs!

a1=; hg diff -r37 9vx/vx32.c
diff -r d945b0921bdc src/9vx/vx32.c
--- a/src/9vx/vx32.c	Sun Jun 29 22:01:07 2008 -0400
+++ b/src/9vx/vx32.c	Sun Jun 29 22:01:55 2008 -0400
@@ -186,6 +186,9 @@ void
 void
 forkret(void)
 {
+	extern void kexit(Ureg*);
+
+	kexit(nil);
 	touser(0);
 }

a1=;