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    Subject[PATCH] override RLIMIT_SIGPENDING for non-RT signals
    Indeed, I think your patch does not go far enough.  I can read POSIX to say
    that the siginfo_t data must be available when `kill' was used, as well.
    This patch makes it allocate the siginfo_t, even when that exceeds
    {RLIMIT_SIGPENDING}, for any non-RT signal (< SIGRTMIN) not sent by
    sigqueue (actually, any signal that couldn't have been faked by a sigqueue
    call). Of course, in an extreme memory shortage situation, you are SOL and
    violate POSIX a little before you die horribly from being out of memory anyway.

    The LEGACY_QUEUE logic already ensures that, for non-RT signals, at most
    one is ever on the queue. So there really is no risk at all of unbounded
    resource consumption; the usage can reach {RLIMIT_SIGPENDING} + 31, is all.

    It's already the case that the limit can be exceeded by (in theory) up to
    {RLIMIT_NPROC}-1 in race conditions because the bump and the limit check
    are not atomic. (Obviously you can only get anywhere near that many with
    assloads of preemption, but exceeding it by a few is not too unlikely.)
    This patch also fixes that accounting so that it should not be possible to
    exceed {RLIMIT_SIGPENDING} + SIGRTMIN-1 queue items per user in races.


    Signed-off-by: Roland McGrath <>

    --- linux-2.6/kernel/signal.c
    +++ linux-2.6/kernel/signal.c
    @@ -260,19 +260,23 @@ next_signal(struct sigpending *pending,
    return sig;

    -static struct sigqueue *__sigqueue_alloc(struct task_struct *t, int flags)
    +static struct sigqueue *__sigqueue_alloc(struct task_struct *t, int flags,
    + int override_rlimit)
    struct sigqueue *q = NULL;

    - if (atomic_read(&t->user->sigpending) <
    + atomic_inc(&t->user->sigpending);
    + if (override_rlimit ||
    + atomic_read(&t->user->sigpending) <=
    q = kmem_cache_alloc(sigqueue_cachep, flags);
    - if (q) {
    + if (unlikely(q == NULL)) {
    + atomic_dec(&t->user->sigpending);
    + } else {
    q->flags = 0;
    q->lock = NULL;
    q->user = get_uid(t->user);
    - atomic_inc(&q->user->sigpending);
    @@ -793,7 +797,9 @@ static int send_signal(int sig, struct s
    make sure at least one signal gets delivered and don't
    pass on the info struct. */

    - q = __sigqueue_alloc(t, GFP_ATOMIC);
    + q = __sigqueue_alloc(t, GFP_ATOMIC, (sig < SIGRTMIN &&
    + ((unsigned long) info < 2 ||
    + info->si_code >= 0)));
    if (q) {
    list_add_tail(&q->list, &signals->list);
    switch ((unsigned long) info) {
    @@ -1316,7 +1322,7 @@ struct sigqueue *sigqueue_alloc(void)
    struct sigqueue *q;

    - if ((q = __sigqueue_alloc(current, GFP_KERNEL)))
    + if ((q = __sigqueue_alloc(current, GFP_KERNEL, 0)))
    q->flags |= SIGQUEUE_PREALLOC;
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      Last update: 2005-03-22 14:10    [W:0.022 / U:11.844 seconds]
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