From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C90DC7EE2A for ; Tue, 6 Jun 2023 14:46:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238163AbjFFOqI (ORCPT ); Tue, 6 Jun 2023 10:46:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47722 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238848AbjFFOpk (ORCPT ); Tue, 6 Jun 2023 10:45:40 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E2E131995 for ; Tue, 6 Jun 2023 07:44:26 -0700 (PDT) Message-ID: <20230606142033.048775731@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1686062296; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=FbfX95bonQ6QuMNiHBaPdEVKsEDfcrvq6gge8bQAWbs=; b=qlPPi2zJ1gOLSHTvVnbN6QCmF6iqPsLJVhZeEwc5YDBdAyQLMp416H3yJCEezDSZnvKfTX hyooItR3CpENkV5UDazbBwUjcGIya+Az8psFl3glrZ1jrtJtIxB9Fu+6syIbjOr7zpA7Cq nCyxdYVLopIwnxhvUDeaj1RDPM2pYklFAo7yIvc99hkCPLsrNhVrSd7NtieS7Ok1u+CjZu CSp7DrEzYcJVUuFnkWoAZI9Y8pUqfa0gBA/eetCjEa1pmGG3BNUTm9+j7bvY1/at6D2P0G 19k7eLR9TDaZUbhlLcr8uldK+n7Orh+g+8UgByCgFkiVpD1viADjgwwReqXltw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1686062296; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=FbfX95bonQ6QuMNiHBaPdEVKsEDfcrvq6gge8bQAWbs=; b=DNdn4sddi0bwxcS7c+BucGdlXd/d1WavXafOwXOJF33YNAMK6P0VbLjtzLhCI5le5LfMMs lzNAd6E0WvZ4bEAg== From: Thomas Gleixner To: LKML Cc: Frederic Weisbecker , Anna-Maria Behnsen , John Stultz , Peter Zijlstra , Ingo Molnar , Stephen Boyd , Eric Biederman , Oleg Nesterov Subject: [patch 36/45] posix-timers: Embed sigqueue in struct k_itimer References: <20230606132949.068951363@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Date: Tue, 6 Jun 2023 16:38:16 +0200 (CEST) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org To cure the SIG_IGN handling for posix interval timers, the preallocated sigqueue needs to be embedded into struct k_itimer to prevent life time races of all sorts. Now that the prerequisites are in place, embed the sigqueue into struct k_itimer and fixup the relevant usage sites. Aside of preparing for proper SIG_IGN handling, this spares an extra allocation. Signed-off-by: Thomas Gleixner --- fs/proc/base.c | 4 +- include/linux/posix-timers.h | 23 +++++++++++++++- kernel/signal.c | 12 +++++++- kernel/time/posix-timers.c | 59 ++++++++++++++++++++++++++----------------- 4 files changed, 69 insertions(+), 29 deletions(-) --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2501,8 +2501,8 @@ static int show_timer(struct seq_file *m seq_printf(m, "ID: %d\n", timer->it_id); seq_printf(m, "signal: %d/%px\n", - timer->sigq->info.si_signo, - timer->sigq->info.si_value.sival_ptr); + timer->sigq.info.si_signo, + timer->sigq.info.si_value.sival_ptr); seq_printf(m, "notify: %s/%s.%d\n", nstr[notify & ~SIGEV_THREAD_ID], (notify & SIGEV_THREAD_ID) ? "tid" : "pid", --- a/include/linux/posix-timers.h +++ b/include/linux/posix-timers.h @@ -63,6 +63,8 @@ static inline int clockid_to_fd(const cl #ifdef CONFIG_POSIX_TIMERS +#include + /** * cpu_timer - Posix CPU timer representation for k_itimer * @node: timerqueue node to queue in the task/sig @@ -228,7 +230,7 @@ static inline void posix_cputimers_init_ * @it_pid: The pid of the process/task targeted by the signal * @it_process: The task to wakeup on clock_nanosleep (CPU timers) * @rcuref: Reference count for life time management - * @sigq: Pointer to preallocated sigqueue + * @sigq: Embedded sigqueue * @it: Union representing the various posix timer type * internals. * @rcu: RCU head for freeing the timer. @@ -252,7 +254,7 @@ struct k_itimer { struct pid *it_pid; struct task_struct *it_process; }; - struct sigqueue *sigq; + struct sigqueue sigq; rcuref_t rcuref; union { struct { @@ -280,6 +282,23 @@ static inline void posixtimer_putref(str if (rcuref_put(&tmr->rcuref)) posixtimer_free_timer(tmr); } + +static inline void posixtimer_sigqueue_getref(struct sigqueue *q) +{ + struct k_itimer *tmr = container_of(q, struct k_itimer, sigq); + + WARN_ON_ONCE(!rcuref_get(&tmr->rcuref)); +} + +static inline void posixtimer_sigqueue_putref(struct sigqueue *q) +{ + struct k_itimer *tmr = container_of(q, struct k_itimer, sigq); + + posixtimer_putref(tmr); +} +#else /* CONFIG_POSIX_TIMERS */ +static inline void posixtimer_sigqueue_getref(struct sigqueue *q) { } +static inline void posixtimer_sigqueue_putref(struct sigqueue *q) { } #endif /* !CONFIG_POSIX_TIMERS */ #endif --- a/kernel/signal.c +++ b/kernel/signal.c @@ -569,7 +569,12 @@ static void collect_signal(int sig, stru still_pending: list_del_init(&first->list); copy_siginfo(info, &first->info); - __sigqueue_free(first); + /* + * Do not drop the reference count for posix timer + * signals. That's done in posix_timer_deliver_signal(). + */ + if (info->si_code != SI_TIMER) + __sigqueue_free(first); } else { /* * Ok, it wasn't in the queue. This must be @@ -1977,7 +1982,7 @@ static inline struct task_struct *posixt int posixtimer_send_sigqueue(struct k_itimer *tmr) { - struct sigqueue *q = tmr->sigq; + struct sigqueue *q = &tmr->sigq; int sig = q->info.si_signo; struct task_struct *t; unsigned long flags; @@ -2037,9 +2042,12 @@ int posixtimer_send_sigqueue(struct k_it ret = 0; if (unlikely(!list_empty(&q->list))) { + /* This holds a reference count already */ result = TRACE_SIGNAL_ALREADY_PENDING; goto out; } + + posixtimer_sigqueue_getref(q); posixtimer_queue_sigqueue(q, t, tmr->it_pid_type); result = TRACE_SIGNAL_DELIVERED; out: --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -251,12 +251,13 @@ static void common_hrtimer_rearm(struct /* * This function is called from the signal delivery code. It decides - * whether the signal should be dropped and rearms interval timers. + * whether the signal should be dropped and rearms interval timers. The + * timer can be unconditionally accessed as there is a reference held on + * it. */ bool posixtimer_deliver_signal(struct kernel_siginfo *info) { - struct k_itimer *timr; - unsigned long flags; + struct k_itimer *timr = info->si_sys_privptr; bool ret = false; /* @@ -264,12 +265,14 @@ bool posixtimer_deliver_signal(struct ke * timr::it_lock. Keep interrupts disabled. */ spin_unlock(¤t->sighand->siglock); + spin_lock(&timr->it_lock); - timr = lock_timer(info->si_tid, &flags); - if (!timr) - goto out; - - if (timr->it_signal_seq != info->si_sys_private) + /* + * Check if the timer is still alive or whether it got modified + * since the signal was queued. In either case, don't rearm and + * drop the signal. + */ + if (!timr->it_signal || timr->it_signal_seq != info->si_sys_private) goto out_unlock; if (timr->it_interval && timr->it_status == POSIX_TIMER_REQUEUE_PENDING) { @@ -285,8 +288,10 @@ bool posixtimer_deliver_signal(struct ke ret = true; out_unlock: - unlock_timer(timr, flags); -out: + spin_unlock(&timr->it_lock); + /* Drop the reference which was acquired when the signal was queued */ + posixtimer_putref(timr); + spin_lock(¤t->sighand->siglock); /* Don't expose the si_sys_priv* values to userspace */ @@ -405,17 +410,17 @@ static struct pid *good_sigevent(sigeven } } -static struct k_itimer * alloc_posix_timer(void) +static struct k_itimer *alloc_posix_timer(void) { struct k_itimer *tmr = kmem_cache_zalloc(posix_timers_cache, GFP_KERNEL); if (!tmr) return tmr; - if (unlikely(!(tmr->sigq = sigqueue_alloc()))) { + + if (unlikely(!posixtimer_init_sigqueue(&tmr->sigq))) { kmem_cache_free(posix_timers_cache, tmr); return NULL; } - clear_siginfo(&tmr->sigq->info); rcuref_init(&tmr->rcuref, 1); return tmr; } @@ -430,7 +435,8 @@ static void k_itimer_rcu_free(struct rcu void posixtimer_free_timer(struct k_itimer *tmr) { put_pid(tmr->it_pid); - sigqueue_free(tmr->sigq); + if (tmr->sigq.ucounts) + dec_rlimit_put_ucounts(tmr->sigq.ucounts, UCOUNT_RLIMIT_SIGPENDING); call_rcu(&tmr->rcu, k_itimer_rcu_free); } @@ -492,13 +498,13 @@ static int do_timer_create(clockid_t whi goto out; } new_timer->it_sigev_notify = event->sigev_notify; - new_timer->sigq->info.si_signo = event->sigev_signo; - new_timer->sigq->info.si_value = event->sigev_value; + new_timer->sigq.info.si_signo = event->sigev_signo; + new_timer->sigq.info.si_value = event->sigev_value; } else { new_timer->it_sigev_notify = SIGEV_SIGNAL; - new_timer->sigq->info.si_signo = SIGALRM; - memset(&new_timer->sigq->info.si_value, 0, sizeof(sigval_t)); - new_timer->sigq->info.si_value.sival_int = new_timer->it_id; + new_timer->sigq.info.si_signo = SIGALRM; + memset(&new_timer->sigq.info.si_value, 0, sizeof(sigval_t)); + new_timer->sigq.info.si_value.sival_int = new_timer->it_id; new_timer->it_pid = get_pid(task_tgid(current)); } @@ -507,10 +513,10 @@ static int do_timer_create(clockid_t whi else new_timer->it_pid_type = PIDTYPE_TGID; - new_timer->sigq->info.si_tid = new_timer->it_id; - new_timer->sigq->info.si_code = SI_TIMER; + new_timer->sigq.info.si_tid = new_timer->it_id; + new_timer->sigq.info.si_code = SI_TIMER; - new_timer->sigq->info.si_sys_privptr = new_timer; + new_timer->sigq.info.si_sys_privptr = new_timer; if (copy_to_user(created_timer_id, &new_timer_id, sizeof (new_timer_id))) { error = -EFAULT; @@ -594,7 +600,14 @@ static struct k_itimer *__lock_timer(tim * 1) Set timr::it_signal to NULL with timr::it_lock held * 2) Release timr::it_lock * 3) Remove from the hash under hash_lock - * 4) Call RCU for removal after the grace period + * 4) Put the reference count. + * + * The reference count might not drop to zero if timr::sigq is + * queued. In that case the signal delivery or flush will put the + * last reference count. + * + * When the reference count reaches zero, the timer is scheduled + * for RCU removal after the grace period. * * Holding rcu_read_lock() accross the lookup ensures that * the timer cannot be freed.