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    Subject[PATCH] sys_unshare: remove a broken CLONE_SIGHAND code
    sys_unshare(CLONE_SIGHAND) is broken, the code under 'if (new_sigh)' is
    never executed but very wrong. Just remove it to avoid a confusion,
    task_lock() has nothing to do with ->sighand changing.

    Also, change the comment in unshare_sighand(). Yes, CLONE_THREAD implies
    CLONE_SIGHAND, but still it looks confusing. Also, we don't need to check
    current->sighand != NULL.

    Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

    --- rc2-mm2/kernel/fork.c~ 2006-10-22 19:28:17.000000000 +0400
    +++ rc2-mm2/kernel/fork.c 2006-10-23 19:23:19.000000000 +0400
    @@ -1523,15 +1523,13 @@ static int unshare_mnt_namespace(unsigne
    }

    /*
    - * Unsharing of sighand for tasks created with CLONE_SIGHAND is not
    - * supported yet
    + * Unsharing of sighand is not supported yet
    */
    static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)
    {
    struct sighand_struct *sigh = current->sighand;

    - if ((unshare_flags & CLONE_SIGHAND) &&
    - (sigh && atomic_read(&sigh->count) > 1))
    + if ((unshare_flags & CLONE_SIGHAND) && atomic_read(&sigh->count) > 1)
    return -EINVAL;
    else
    return 0;
    @@ -1605,7 +1603,7 @@ asmlinkage long sys_unshare(unsigned lon
    int err = 0;
    struct fs_struct *fs, *new_fs = NULL;
    struct mnt_namespace *ns, *new_ns = NULL;
    - struct sighand_struct *sigh, *new_sigh = NULL;
    + struct sighand_struct *new_sigh = NULL;
    struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;
    struct files_struct *fd, *new_fd = NULL;
    struct sem_undo_list *new_ulist = NULL;
    @@ -1650,7 +1648,7 @@ asmlinkage long sys_unshare(unsigned lon
    }
    }

    - if (new_fs || new_ns || new_sigh || new_mm || new_fd || new_ulist ||
    + if (new_fs || new_ns || new_mm || new_fd || new_ulist ||
    new_uts || new_ipc) {

    task_lock(current);
    @@ -1672,12 +1670,6 @@ asmlinkage long sys_unshare(unsigned lon
    new_ns = ns;
    }

    - if (new_sigh) {
    - sigh = current->sighand;
    - rcu_assign_pointer(current->sighand, new_sigh);
    - new_sigh = sigh;
    - }
    -
    if (new_mm) {
    mm = current->mm;
    active_mm = current->active_mm;
    -
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