Re: 3.4-rc7: BUG: Bad rss-counter state mm:ffff88040b56f800 idx:1val:-59

[Konstantin Khlebnikov]

Konstantin Khlebnikov wrote:
> Martin Mokrejs wrote:
> > Konstantin Khlebnikov wrote:
> > > Martin Mokrejs wrote:
> > > > Andrew Morton wrote:
> > > > > On Wed, 30 May 2012 00:18:31 +0400
> > > > > Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx>    wrote:
> > > > >
> > > > > > Oleg Nesterov wrote:
> > > > > > > On 05/22, Andrew Morton wrote:
> > > > > > > > Also, I have a note here that Oleg was unhappy with the patch.  Oleg
> > > > > > > > happiness is important.  Has he cheered up yet?
> > > > > > >
> > > > > > > Well, yes, I do not really like this patch ;) Because I think there is
> > > > > > > a more simple/straightforward fix, see below. In my opinion it also
> > > > > > > makes the original code simpler.
> > > > > > >
> > > > > > > But. Obviously this is subjective, I can't prove my patch is "better",
> > > > > > > and I didn't try to test it.
> > > > > > >
> > > > > > > So I won't argue with Konstantin who dislikes my patch, although I
> > > > > > > would like to know the reason.
> > > > > >
> > > > > > I don't remember why I dislike your patch.
> > > > > > For now I can only say ACK )
> > > > >
> > > > > We'll need a changelogged signed-off patch, please Oleg.  And some evidence
> > > > > that it was tested would be nice ;)
> > > >
> > > > I will reboot in few hours, finally after few days ... I am running this first
> > > > patch. I will try to test the second/alternative patch more quickly. Sorry for
> > > > the delay.
> > >
> > > easiest way trigger this bug:
> > >
> > > #define _GNU_SOURCE
> > > #include<unistd.h>
> > > #include<sched.h>
> > > #include<sys/syscall.h>
> > > #include<sys/mman.h>
> > >
> > > static inline int sys_clone(unsigned long flags, void *stack, int *ptid, int *ctid)
> > > {
> > >       return syscall(SYS_clone, flags, stack, ptid, ctid);
> > > }
> > >
> > > int main(int argc, char **argv)
> > > {
> > >       void *page;
> > >
> > >       page = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
> > >       sys_clone(CLONE_VFORK | CLONE_VM | CLONE_CHILD_CLEARTID, NULL, NULL, page);
> > > }
> >
> > I am getting segfaults with this.
> >
> > (gdb) where
> > #0  0x0000000000000000 in ?? ()
> > #1  0x00007f430f70a7e0 in __elf_set___libc_subfreeres_element_free_mem__ () from /lib64/libc.so.6
> > #2  0x00007f430f70a7e8 in __elf_set___libc_atexit_element__IO_cleanup__ () from /lib64/libc.so.6
> > #3  0x0000000000000001 in ?? ()
> > #4  0x0000000000000000 in ?? ()
> > (gdb)
> >
> > What number should I give it as an argument? ;-)
>
> there is no arguments.
>
> yeah it corrupts stack. I'm too lazy to write it properly =)
> but on non-patched kernel it also triggers this bug:
> [206732.025131] BUG: Bad rss-counter state mm:ffff88000d8a6c80 idx:1 val:-1
>
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this version works without segfaults =)

#define _GNU_SOURCE
#include <stdlib.h>
#include <sched.h>
#include <sys/mman.h>

int child(void *arg)
{
	return 0;
}

char stack[4096];

int main(int argc, char **argv)
{
	void *page;

	page = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
	clone(child, stack + sizeof(stack), CLONE_VFORK | CLONE_VM | CLONE_CHILD_CLEARTID, NULL, NULL, NULL, page);
	return 0;
}

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