From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87AF8288534; Mon, 5 May 2025 23:05:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746486309; cv=none; b=XwoomoaKMmMMv+H+prZev50X0tJoAX3zS1yH991yq1xNuuDyUifRtR/9ILfcDINpaNE8MvDAldijdPCa2FZob47etpcxD0twWEVIiPfIH8wQSCrRZStCIJUNqWrqP23kP2iTAqnFcGIWV3Nmo2lk1jnMTFo0g10lNpxhRN9rwi0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746486309; c=relaxed/simple; bh=6BmnCNBbfLfoySlSwNtn0q29baarrlkHdad1Zgjlyyo=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=gZcKVMmfJqwimsfJCe3aJqD3qobLcnlnarW4Q1ecruiWcplLZiQxmtqO07ccGdasPxIiawy0qNYy3tS5ZSs4/nQKJmrb2dDXKHU1vPXL64CZsD2UjaoozDtmPZsssVd5oVHVVcptM8mUMhI1W2YFfQ9q9xyMTQdgVrqLQ/kjoi4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Fq73F4sc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Fq73F4sc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1CA27C4CEE4; Mon, 5 May 2025 23:05:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746486308; bh=6BmnCNBbfLfoySlSwNtn0q29baarrlkHdad1Zgjlyyo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Fq73F4scMLjJceCWTdvqOaDhjvkoWvln7M2rrSXb5mzfawZXqrnZUjd2LVaJcgSfV SPh6HTMO96mfKqdGI8pP4IIeQqpHIWCmcNU9H0XUsu1AmDJYN4kSkeVtnMJIUVnwll JW5L/X69lE36joYCJId5KmLGf8fWTJLHD3Uc59et28QCo3qv09LbzhdSzJBI+eYCkj WNsl+rHwCgbYizTq1wlpEx/Xf71TyMxuLjLmK9MB8QjAH3G1hZRtf9KalKfG5c1cT9 E1UGPhx/e6GVFWNJ0AZVCoiJRwsRxa1uHQc3nZg32m9Fzcvc4rnDNaXUOnZ+2RCHjD co5KP1QX+9zmQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , Frederic Weisbecker , Christian Brauner , Sasha Levin , akpm@linux-foundation.org, mhocko@suse.com, Liam.Howlett@Oracle.com, mjguzik@gmail.com, alexjlzheng@tencent.com, pasha.tatashin@soleen.com Subject: [PATCH AUTOSEL 6.6 251/294] exit: change the release_task() paths to call flush_sigqueue() lockless Date: Mon, 5 May 2025 18:55:51 -0400 Message-Id: <20250505225634.2688578-251-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250505225634.2688578-1-sashal@kernel.org> References: <20250505225634.2688578-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.6.89 Content-Transfer-Encoding: 8bit From: Oleg Nesterov [ Upstream commit fb3bbcfe344e64a46574a638b051ffd78762c12d ] A task can block a signal, accumulate up to RLIMIT_SIGPENDING sigqueues, and exit. In this case __exit_signal()->flush_sigqueue() called with irqs disabled can trigger a hard lockup, see https://lore.kernel.org/all/20190322114917.GC28876@redhat.com/ Fortunately, after the recent posixtimer changes sys_timer_delete() paths no longer try to clear SIGQUEUE_PREALLOC and/or free tmr->sigq, and after the exiting task passes __exit_signal() lock_task_sighand() can't succeed and pid_task(tmr->it_pid) will return NULL. This means that after __exit_signal(tsk) nobody can play with tsk->pending or (if group_dead) with tsk->signal->shared_pending, so release_task() can safely call flush_sigqueue() after write_unlock_irq(&tasklist_lock). TODO: - we can probably shift posix_cpu_timers_exit() as well - do_sigaction() can hit the similar problem Signed-off-by: Oleg Nesterov Link: https://lore.kernel.org/r/20250206152314.GA14620@redhat.com Reviewed-by: Frederic Weisbecker Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin --- kernel/exit.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 1b7257c12cb10..6c75c823de25c 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -199,20 +199,13 @@ static void __exit_signal(struct task_struct *tsk) __unhash_process(tsk, group_dead); write_sequnlock(&sig->stats_lock); - /* - * Do this under ->siglock, we can race with another thread - * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals. - */ - flush_sigqueue(&tsk->pending); tsk->sighand = NULL; spin_unlock(&sighand->siglock); __cleanup_sighand(sighand); clear_tsk_thread_flag(tsk, TIF_SIGPENDING); - if (group_dead) { - flush_sigqueue(&sig->shared_pending); + if (group_dead) tty_kref_put(tty); - } } static void delayed_put_task_struct(struct rcu_head *rhp) @@ -282,6 +275,16 @@ void release_task(struct task_struct *p) proc_flush_pid(thread_pid); put_pid(thread_pid); release_thread(p); + /* + * This task was already removed from the process/thread/pid lists + * and lock_task_sighand(p) can't succeed. Nobody else can touch + * ->pending or, if group dead, signal->shared_pending. We can call + * flush_sigqueue() lockless. + */ + flush_sigqueue(&p->pending); + if (thread_group_leader(p)) + flush_sigqueue(&p->signal->shared_pending); + put_task_struct_rcu_user(p); p = leader; -- 2.39.5