linux-kernel - Re: [RFC][PATCH 4/6][v3] Define siginfo_from_ancestor

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Date:	Tue, 23 Dec 2008 00:54:58 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	ebiederm@...ssion.com, roland@...hat.com, bastian@...di.eu.org,
	daniel@...ac.com, xemul@...nvz.org, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org, sukadev@...ibm.com
Subject: Re: [RFC][PATCH 4/6][v3] Define siginfo_from_ancestor_ns()

On 12/22, Sukadev Bhattiprolu wrote:
>
> Oleg Nesterov [oleg@...hat.com] wrote:
> | On 12/20, Sukadev Bhattiprolu wrote:
> | >
> | > + * TODO:
> | > + * 	  Making SI_ASYNCIO a kernel signal could make this less hacky.
> | > + */
> | > +#ifdef CONFIG_PID_NS
> | > +static inline int siginfo_from_user(siginfo_t *info)
> | > +{
> | > +	if (!is_si_special(info) && SI_FROMUSER(info) &&
> |
> | OK, if we can trust SI_FROMUSER(), then it is better, i agree.
> |
> | I was worried about in-kernel usage of .si_code <= 0 ...
> |
> | > +				info->si_code != SI_ASYNCIO)
> |
> | but this is horrible, imho.
>
> I am beginning to accept that some amount of ugliness is inevitable
> here :-)

heh, agreed...

> I tried to dig through history of SI_ASYNCIO, but did not
> find any changes to its definition in siginfo.h in 6 years.

basically, it was needed (afaics) because we didn't have "struct pid"
when the patch was sent. Commit 46113830a18847cff8da73005e57bc49c2f95a56

(but the fact that SI_FROMUSER(SI_ASYNCIO) == T is imho unforgivable ;)

> | OK, if we can't change the ABI, then perhaps we can change
> | kill_pid_info_as_uid() to not send the fatal signals to UNKILLABLE
> | task? This helper is strange and ugly anyway,
> |
> |
> | To clarify, I do not blame the patch itself, and I do not suggest
> | to do this right now.
>
> By 'to do this' I assume you are referring to the kill_pid_info_as_uid()
> change above ?
>
> IOW, ugly as it is, can we go with the siginfo_from_user() as in the patch ?

Yes. Sorry if I was not clear. I think that this part of patch is imho
horrible, but we should blame drivers/usb/core/devio.c. I'd personally
like to move the uglification to kill_pid_info_as_uid(), but we can do
this later.

Oleg.

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