linux-kernel - Re: x86: do_debug && PTRACE_SINGLESTEP broken by 08d68323d1f0c34452e614263b212ca556dae47f

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Message-ID: <20091218175842.GA10666@in.ibm.com>
Date:	Fri, 18 Dec 2009 23:28:42 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, utrace-devel@...hat.com
Subject: Re: x86: do_debug && PTRACE_SINGLESTEP broken by
	08d68323d1f0c34452e614263b212ca556dae47f

On Fri, Dec 18, 2009 at 06:27:47PM +0100, Oleg Nesterov wrote:
> On 12/18, Frederic Weisbecker wrote:
> >
> > On Fri, Dec 18, 2009 at 01:56:50AM +0100, Oleg Nesterov wrote:
> > > Hi.

<snipped>

> > Single stepping works well for me, after a quick check on
> > gdb. How did you trigger the bug?
> 
> Please find the trivial test-case below. It hangs, because
> PTRACE_SINGLESTEP doesn't trigger the trap.
> 

aah...my other mail just criss-crossed yours.

I quickly ran on the said x86 box, loaded with -tip (commit
7818b3d0fc68f5c2a85fed86d9fa37131c5a3068) and it runs fine.

[root@...05 prasadkr]# cat oleg.c
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <assert.h>

int main(void)
{
        int pid, status, i;

        pid = fork();
        if (!pid)
                for (;;);

        sleep(1);
        assert(ptrace(PTRACE_ATTACH, pid, 0,0) == 0);

        assert(pid == wait(&status));
        assert(WIFSTOPPED(status));

        for (i = 0; i < 10; ++i) {
                assert(ptrace(PTRACE_SINGLESTEP, pid, 0,0) == 0);

                printf("wait %d ...\n", i);
                assert(pid == wait(&status));

                assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGTRAP);
       	}

        kill(pid, SIGKILL);
        return 0;
}

[root@...05 prasadkr]# gcc -o oleg oleg.c -g -Wall
[root@...05 prasadkr]# ./oleg
wait 0 ...
wait 1 ...
wait 2 ...
wait 3 ...
wait 4 ...
wait 5 ...
wait 6 ...
wait 7 ...
wait 8 ...
wait 9 ...
[root@...05 prasadkr]# 

Am I missing something here?

Thanks,
K.Prasad

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