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    Subject[patch 07/28] signalfd: make it group-wide, fix posix-timers scheduling
    -stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Oleg Nesterov <oleg@tv-sign.ru>

    With this patch any thread can dequeue its own private signals via signalfd,
    even if it was created by another sub-thread.

    To do so, we pass "current" to dequeue_signal() if the caller is from the same
    thread group. This also fixes the scheduling of posix timers broken by the
    previous patch.

    If the caller doesn't belong to this thread group, we can't handle __SI_TIMER
    case properly anyway. Perhaps we should forbid the cross-process signalfd usage
    and convert ctx->tsk to ctx->sighand.

    Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Davide Libenzi <davidel@xmailserver.org>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Michael Kerrisk <mtk-manpages@gmx.net>
    Cc: Roland McGrath <roland@redhat.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/exec.c | 9 ++-------
    fs/signalfd.c | 14 ++++++++++----
    2 files changed, 12 insertions(+), 11 deletions(-)

    --- a/fs/exec.c
    +++ b/fs/exec.c
    @@ -586,18 +586,12 @@ static int de_thread(struct task_struct
    int count;

    /*
    - * Tell all the sighand listeners that this sighand has
    - * been detached. The signalfd_detach() function grabs the
    - * sighand lock, if signal listeners are present on the sighand.
    - */
    - signalfd_detach(tsk);
    -
    - /*
    * If we don't share sighandlers, then we aren't sharing anything
    * and we can just re-use it all.
    */
    if (atomic_read(&oldsighand->count) <= 1) {
    BUG_ON(atomic_read(&sig->count) != 1);
    + signalfd_detach(tsk);
    exit_itimers(sig);
    return 0;
    }
    @@ -736,6 +730,7 @@ static int de_thread(struct task_struct
    sig->flags = 0;

    no_thread_group:
    + signalfd_detach(tsk);
    exit_itimers(sig);
    if (leader)
    release_task(leader);
    --- a/fs/signalfd.c
    +++ b/fs/signalfd.c
    @@ -56,12 +56,18 @@ static int signalfd_lock(struct signalfd
    sighand = lock_task_sighand(lk->tsk, &lk->flags);
    rcu_read_unlock();

    - if (sighand && !ctx->tsk) {
    + if (!sighand)
    + return 0;
    +
    + if (!ctx->tsk) {
    unlock_task_sighand(lk->tsk, &lk->flags);
    - sighand = NULL;
    + return 0;
    }

    - return sighand != NULL;
    + if (lk->tsk->tgid == current->tgid)
    + lk->tsk = current;
    +
    + return 1;
    }

    static void signalfd_unlock(struct signalfd_lockctx *lk)
    @@ -331,7 +337,7 @@ asmlinkage long sys_signalfd(int ufd, si

    init_waitqueue_head(&ctx->wqh);
    ctx->sigmask = sigmask;
    - ctx->tsk = current;
    + ctx->tsk = current->group_leader;

    sighand = current->sighand;
    /*
    --
    -
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