From patchwork Mon Aug 24 08:31:13 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 265051 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0F4FEC433DF for ; Mon, 24 Aug 2020 09:33:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC902206F0 for ; Mon, 24 Aug 2020 09:33:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598261622; bh=BYU4VwRM5xFvzKpaDfvkbDeIvtDQMxsMNHx+jb8xCq8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=qRkAnGjGY5816/EUGFE4yM5Wg7Rdr/8xgoi5YyFd06R5IK8Ba1ZQlxrAoJEwCO2FE 0nhV1kKH+9FwRXzU01Oi+ygJMXjvowAlvRC8/RiJJwrgR/S9l7/+0URwlx+kt/2Z91 tJUo1XKjNHAJuzD4iWGQk0NrzgQ+lNQvoNJUp+ew= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729754AbgHXItl (ORCPT ); Mon, 24 Aug 2020 04:49:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:52184 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729748AbgHXIth (ORCPT ); Mon, 24 Aug 2020 04:49:37 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3F4422072D; Mon, 24 Aug 2020 08:49:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598258976; bh=BYU4VwRM5xFvzKpaDfvkbDeIvtDQMxsMNHx+jb8xCq8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z5uxX6Nv8PNIQ/Oz0d4rXsDWfu+u3d89hZL1i02PZxYcmrT5dw/Ph/27o2hT65bIO PT36/V8XvUxgJQoJpQS3jvH7myrzAXwYJ6sMPj1JhiJaAduaKUGl6Ww94rB6bBh+r4 cWcB4C1qyDZ/xBn/LawZWbsPs2GOQ00Th+zJp/Po= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , Sarah Newman , Juergen Gross , Chris Brannon Subject: [PATCH 5.4 107/107] xen: dont reschedule in preemption off sections Date: Mon, 24 Aug 2020 10:31:13 +0200 Message-Id: <20200824082410.383029726@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200824082405.020301642@linuxfoundation.org> References: <20200824082405.020301642@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Juergen Gross For support of long running hypercalls xen_maybe_preempt_hcall() is calling cond_resched() in case a hypercall marked as preemptible has been interrupted. Normally this is no problem, as only hypercalls done via some ioctl()s are marked to be preemptible. In rare cases when during such a preemptible hypercall an interrupt occurs and any softirq action is started from irq_exit(), a further hypercall issued by the softirq handler will be regarded to be preemptible, too. This might lead to rescheduling in spite of the softirq handler potentially having set preempt_disable(), leading to splats like: BUG: sleeping function called from invalid context at drivers/xen/preempt.c:37 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 20775, name: xl INFO: lockdep is turned off. CPU: 1 PID: 20775 Comm: xl Tainted: G D W 5.4.46-1_prgmr_debug.el7.x86_64 #1 Call Trace: dump_stack+0x8f/0xd0 ___might_sleep.cold.76+0xb2/0x103 xen_maybe_preempt_hcall+0x48/0x70 xen_do_hypervisor_callback+0x37/0x40 RIP: e030:xen_hypercall_xen_version+0xa/0x20 Code: ... RSP: e02b:ffffc900400dcc30 EFLAGS: 00000246 RAX: 000000000004000d RBX: 0000000000000200 RCX: ffffffff8100122a RDX: ffff88812e788000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffffff83ee3ad0 R08: 0000000000000001 R09: 0000000000000001 R10: 0000000000000000 R11: 0000000000000246 R12: ffff8881824aa0b0 R13: 0000000865496000 R14: 0000000865496000 R15: ffff88815d040000 ? xen_hypercall_xen_version+0xa/0x20 ? xen_force_evtchn_callback+0x9/0x10 ? check_events+0x12/0x20 ? xen_restore_fl_direct+0x1f/0x20 ? _raw_spin_unlock_irqrestore+0x53/0x60 ? debug_dma_sync_single_for_cpu+0x91/0xc0 ? _raw_spin_unlock_irqrestore+0x53/0x60 ? xen_swiotlb_sync_single_for_cpu+0x3d/0x140 ? mlx4_en_process_rx_cq+0x6b6/0x1110 [mlx4_en] ? mlx4_en_poll_rx_cq+0x64/0x100 [mlx4_en] ? net_rx_action+0x151/0x4a0 ? __do_softirq+0xed/0x55b ? irq_exit+0xea/0x100 ? xen_evtchn_do_upcall+0x2c/0x40 ? xen_do_hypervisor_callback+0x29/0x40 ? xen_hypercall_domctl+0xa/0x20 ? xen_hypercall_domctl+0x8/0x20 ? privcmd_ioctl+0x221/0x990 [xen_privcmd] ? do_vfs_ioctl+0xa5/0x6f0 ? ksys_ioctl+0x60/0x90 ? trace_hardirqs_off_thunk+0x1a/0x20 ? __x64_sys_ioctl+0x16/0x20 ? do_syscall_64+0x62/0x250 ? entry_SYSCALL_64_after_hwframe+0x49/0xbe Fix that by testing preempt_count() before calling cond_resched(). In kernel 5.8 this can't happen any more due to the entry code rework (more than 100 patches, so not a candidate for backporting). The issue was introduced in kernel 4.3, so this patch should go into all stable kernels in [4.3 ... 5.7]. Reported-by: Sarah Newman Fixes: 0fa2f5cb2b0ecd8 ("sched/preempt, xen: Use need_resched() instead of should_resched()") Cc: Sarah Newman Cc: stable@vger.kernel.org Signed-off-by: Juergen Gross Tested-by: Chris Brannon Signed-off-by: Greg Kroah-Hartman --- drivers/xen/preempt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/xen/preempt.c +++ b/drivers/xen/preempt.c @@ -27,7 +27,7 @@ EXPORT_SYMBOL_GPL(xen_in_preemptible_hca asmlinkage __visible void xen_maybe_preempt_hcall(void) { if (unlikely(__this_cpu_read(xen_in_preemptible_hcall) - && need_resched())) { + && need_resched() && !preempt_count())) { /* * Clear flag as we may be rescheduled on a different * cpu.