Re: [patch] fix for OOM deadlock in swap_in (2.2.10) [Re: [testprogram] for OOM situations ]

[Linus Torvalds <torvalds@transmeta.com>]

On Sun, 4 Jul 1999, Rik van Riel wrote:

> On Sat, 3 Jul 1999, Andrea Arcangeli wrote:
> 
> > +void oom(void)
> >  {
> ...
> > +	force_sig(SIGKILL, current);
> 
> > I would like to get some feedback about the patch. Thanks :).
> 
> I'm curious why you haven't yet included my process
> selection algoritm. I know it can select a blocked
> or otherwise unkillable process the way the code is
> in right now, but a workaround for that can be made
> in about 5 minutes.

Andreas patch has a much more serious problem: it changes accepted UNIX
semantics. Try this before and after the patch:

#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>

#define PAGE_SIZE 4096

int main(int argc, char **argv)
{
        int fd;
        char * map;

        fd = open("/tmp/duh", O_RDWR | O_CREAT, 0666);
        if (fd < 0)
                exit(1);
        ftruncate(fd, PAGE_SIZE);
        map = mmap(NULL, PAGE_SIZE*2, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
        *(volatile char *)(map+PAGE_SIZE);
        return 0;
}

and see the difference..

I have tried to fix this _correctly_ in 2.3.10-pre2. That fix could be
back-ported to 2.2.x, but Andreas patch really is not acceptable.

And Andrea, I told you this once already in private email. I told you why.
Why don't you listen? "Fixing" a bug badly is worse than leaving it as a
known bug.

		Linus

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