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    SubjectRe: Testing lxc 0.6.5 in Fedora 13
    On wto, mar 23, 2010 at 02:28:34 -0700, Matt Helsley wrote:
    > On Sun, Mar 21, 2010 at 08:50:44PM +0100, Grzegorz Nosek wrote:
    >
    > <snip>
    >
    > > 2. Weird strace behaviour across pidns boundary
    > >
    > > When strace'ing (with -ff) lxc-start, I get a proper strace for the
    > > directly spawned process and the container init. However, any processes
    > > spawned by the container's init are not straced properly (I get two
    > > empty files, named <foo>.<pid-in-root-ns> and <foo>.2 -- presumably pid
    > > inside the container). The container also seems to malfunction under
    > > strace (looks like exec() failing as lxc-ps shows two "init" processes).
    > >
    > > This is quite painful as it prevents strace'ing processes in containers
    > > even after startup. Here's a snippet of strace'ing a bash (pid 179
    > > inside, pid 2959 outside) trying to run 'ls'. The shell hangs until I
    > > kill the strace process.
    > >
    > > pipe([3, 4]) = 0
    > > clone(Process 197 attached
    > > child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0xb7859708) = 197
    > > Process 2999 attached (waiting for parent)
    > > [pid 2959] setpgid(197, 197) = 0
    > > [pid 2959] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
    > > [pid 2959] rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
    > > [pid 2959] close(3) = 0
    > > [pid 2959] close(4) = 0
    > > [pid 2959] rt_sigprocmask(SIG_BLOCK, [CHLD TSTP TTIN TTOU], [CHLD], 8) = 0
    > > [pid 2959] ioctl(255, TIOCSPGRP, [197]) = 0
    > > [pid 2959] rt_sigprocmask(SIG_SETMASK, [CHLD], NULL, 8) = 0
    > > [pid 2959] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
    > > [pid 2959] rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
    > > [pid 2959] waitpid(-1, Process 2959 suspended
    > > ^C <unfinished ...>
    > > Process 2959 detached
    > > Process 197 detached
    > > Process 2999 detached
    > >
    > > 'strace ls' ran completely inside the container works as expected.
    >
    > I'm suprised strace of ls works across pid namespaces. I've been looking
    > at strace and it seemed to me that one kernel change and a bunch of strace
    > changes are needed to make strace'ing in child pid namespaces work. Eric
    > Biederman's setns() patches also might help.

    Thanks for the patch and the detailed explanation.

    > Can you get a little farther with the kernel fix below?

    No, not really. Attaching from outside to a shell running in a container
    and running a command yields:

    | rt_sigprocmask(SIG_BLOCK, [INT CHLD], [], 8) = 0
    | pipe([3, 4]) = 0
    | clone(Process 2581 attached (waiting for parent)
    | Process 190 attached

    Without the patch the order of reported pids is reversed (and at least
    with the patched kernel the outside pid is consistently reported first)

    | child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0xb7713708) = 190
    | [pid 2549] setpgid(190, 190) = 0
    | [pid 2549] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
    | [pid 2549] rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
    | [pid 2549] close(3) = 0
    | [pid 2549] close(4) = 0
    | [pid 2549] rt_sigprocmask(SIG_BLOCK, [CHLD TSTP TTIN TTOU], [CHLD], 8) = 0
    | [pid 2549] ioctl(255, TIOCSPGRP, [190]) = 0
    | [pid 2549] rt_sigprocmask(SIG_SETMASK, [CHLD], NULL, 8) = 0
    | [pid 2549] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
    | [pid 2549] rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
    | [pid 2549] waitpid(-1, Process 2549 suspended

    (the shell hangs here)

    ^C <unfinished ...>
    | Process 2549 detached
    | Process 2581 detached
    | Process 190 detached

    (the command executes here normally).

    Best regards,
    Grzegorz Nosek


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