Hi Linus,
On 22/06/21 11:14 am, Linus Torvalds wrote:
On Mon, Jun 21, 2021 at 12:45 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
Looks like sys_exit() and do_group_exit() would be the two places to
do it (do_group_exit() would handle the signal case and
sys_group_exit()).
Maybe... I'm digging through that pile right now, will follow up when
I get a reasonably complete picture
We might have another possible way to solve this:
(a) make it the rule that everybody always saves the full (integer)
register set in pt_regs
(b) make m68k just always create that switch-stack for all system
calls (it's really not that big, I think it's like six words or
something)
Correct - six words for registers, one for the return address. Probably
still a win compared to setting and clearing flag bits all over the
place in an attempt to catch any as yet undetected unsafe cases of
ptrace_stop.
I'll have to see how much of a performance impact I can see (not that I
can even remotely measure that accurately - it's more of a 'does it now
feel real sluggish' thing).
Cheers,
Michael
(c) admit that alpha is broken, but nobody really cares
In the meanwhile, do kernel/kthread.c uses look even remotely sane?
Intentional - sure, but it really looks wrong to use thread exit code
as communication channel there...
I really doubt that it is even "intentional".
I think it's "use some errno as a random exit code" and nobody ever
really thought about it, or thought about how that doesn't really
work. People are used to the error numbers, not thinking about how
do_exit() doesn't take an error number, but a signal number (and an
8-bit positive error code in bits 8-15).
Because no, it's not even remotely sane.
I think the do_exit(-EINTR) could be do_exit(SIGINT) and it would make
more sense. And the -ENOMEM might be SIGBUS, perhaps.
It does look like the usermode-helper code does save the exit code
with things like
kernel_wait(pid, &sub_info->retval);
and I see call_usermodehelper_exec() doing
retval = sub_info->retval;
and treating it as an error code. But I think those have never been
tested with that (bogus) exit code thing from kernel_wait(), because
it wouldn't have worked. It has only ever been tested with the (real)
exit code things like
if (pid < 0) {
sub_info->retval = pid;
which does actually assign a negative error code to it.
So I think that
kernel_wait(pid, &sub_info->retval);
line is buggy, and should be something like
int wstatus;
kernel_wait(pid, &wstatus);
sub_info->retval = WEXITSTATUS(wstatus) ? -EINVAL : 0;
or something.
Linus
