Re: [RFC][PATCH -mm] replace cad_pid by a struct pid

Cedric Le Goater
2006-09-21T13:21:29Z

Hello,

Andrew Morton wrote:
> On Wed, 20 Sep 2006 11:38:35 +0200
> Cedric Le Goater <clg@fr.ibm.com> wrote:
>
>> There are a few places in the kernel where the init task is
>> signaled. The ctrl+alt+del sequence is one them. It kills a task,
>> usually init, using a cached pid (cad_pid).
>>
>> This patch replaces the pid_t by a struct pid to avoid pid wrap around
>> problem. The struct pid is initialized at boot time in init() and can
>> be modified through systctl with
>>
>> /proc/sys/kernel/cad_pid
>
> hm. Is there any sane scenario in which C-A-D would be directed to any
> other process?

I don't know. I really looked hard to see where this was used and i didn't
find any distro using it.

> What happens if/when the process which is identifier by
> /proc/sys/kernel/cad_pid exits? User error, I guess...

kill_pid() fails.

>> +extern struct pid* cad_pid;
>
> Whitespace violation detected!
>
>> - if (shuting_down || kill_proc(1, SIGINT, 1)) {
>> + if (shuting_down || kill_cad_pid(SIGINT, 1)) {
>
> So your patch actually makes functional changes: lots of random
> init-signallers gain extra functionality: the process which they signal can
> now be configured via /proc/sys/kernel/cad_pid. But by default, things
> remain unchanged. Fair enough.

yes.

>> --- 2.6.18-rc7-mm1.orig/drivers/char/nwbutton.c
>> +++ 2.6.18-rc7-mm1/drivers/char/nwbutton.c
>
> This driver can be compiled as a module. I shall add the missing export...

oops thanks,

> (And I'll fix the parisc build too)

the only parisc i have still runs its native hpux 11.

do we still need /proc/sys/kernel/cad_pid ? If it is obsolete, i'd send a
different patch to disable this feature with some warning in dmesg and the
kill_proc(1) would stay as they are.

but may be some small distros for embedded linux use it.

thanks,

C.