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    SubjectRe: [PATCH 3/3] fs/locks: Use fs-specific l_pid for remote locks
    Date
    Apologies for the delayed response..

    On 7 Jun 2017, at 7:40, Jeff Layton wrote:

    > On Tue, 2017-06-06 at 16:45 -0400, Benjamin Coddington wrote:
    >> Now that we're translating fl_pid for F_GETLK and /proc/locks, we need to
    >> handle the case where a remote filesystem directly sets fl_pid. In that
    >> case, the fl_pid should not be translated into a local pid namespace. If
    >> the filesystem implements the lock operation, set a flag to return the
    >> lock's fl_pid value directly, rather translate it.
    >>
    >
    > Actually, you're not translating anything for F_GETLK until we get to
    > this patch. Patch #2 in this series removes the fl_nspid field, but the
    > pid translation isn't fixed until here. That does mean a nominal
    > regression here in how fl_pid is reported between the two.

    Good catch.

    > Would it be best to squash #2 and #3 together? Or maybe just go ahead
    > and universally translate the fl_pid field until you add the flag in
    > this patch?

    I'll send a v4 that universally translates the fl_pid field until this
    patch. I think the first two patches should be separate.

    > Also to make sure I understand: task->tgid will always represent the
    > task's pid in the init_pid_ns, right?

    Yes. (I was incorrect on IRC last week), as is seen in kernel/fork.c:
    1748 if (pid != &init_struct_pid) {
    1749 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
    ...
    1754 }
    ...
    1785 p->pid = pid_nr(pid);
    1786 if (clone_flags & CLONE_THREAD) {
    ...
    1789 p->tgid = current->tgid;
    1790 } else {
    ...
    1796 p->tgid = p->pid;
    1797 }

    .. and include/linux/pid.h:
    153 /*
    154 * the helpers to get the pid's id seen from different namespaces
    ...
    156 * pid_nr() : global id, i.e. the id seen from the init namespace;
    ...
    162 */
    163
    164 static inline pid_t pid_nr(struct pid *pid)
    165 {
    166 pid_t nr = 0;
    167 if (pid)
    168 nr = pid->numbers[0].nr;
    169 return nr;
    170 }

    Ben

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