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SubjectRe: Linux 2.6.38
On 03/14, David Rientjes wrote:
>
> He also presented a test case on linux-mm that caused the oom killer to
> avoid acting if a thread is ptracing a thread in the exit path with
> PTRACE_O_TRACEEXIT. That should be fixed with
>
> http://marc.info/?l=linux-mm&m=129997893430351

I don't think it can fix this. I didn't verify this, but the slightly
different test-case below should have the same effect.
But this doesn't matter. We can fix this particular case, and we have
the problems with the coredump anyway.

What I can't understand is what exactly the first patch tries to fix.
When I ask you, you tell me that for_each_process() can miss the group
leader because it can exit before sub-threads. This must not happen,
or we have some serious bug triggered by your workload.

So, once again. Could you please explain the original problem and how
this patch helps?

Oleg.

#include <unistd.h>
#include <signal.h>
#include <pthread.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <assert.h>
#include <stdio.h>

void *tfunc(void* arg)
{
if (arg) {
ptrace(PTRACE_TRACEME, 0,0,0);
raise(SIGSTOP);
pthread_kill(*(pthread_t*)arg, SIGQUIT);
}
pause();
}
int main(void)
{
int pid;
if (!fork()) {
pthread_t thread1, thread2;
pthread_create(&thread1, NULL, tfunc, NULL);
pthread_create(&thread2, NULL, tfunc, &thread1);
pause();
return 0;
}
assert((pid = waitpid(-1, NULL, __WALL)) > 0);
assert(ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_TRACEEXIT) == 0);
assert(ptrace(PTRACE_CONT, pid, 0, 0) == 0);
wait(NULL);
pause();
return 0;
}


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