From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757481AbdDRUtI (ORCPT ); Tue, 18 Apr 2017 16:49:08 -0400 Received: from fllnx210.ext.ti.com ([198.47.19.17]:60701 "EHLO fllnx210.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754018AbdDRUtF (ORCPT ); Tue, 18 Apr 2017 16:49:05 -0400 From: Grygorii Strashko To: Russell King , Sebastian Andrzej Siewior , CC: , , Grygorii Strashko , Kees Cook , Laura Abbott Subject: [v4.9-rt PATCH] ARM: mm: remove tasklist locking from update_sections_early() Date: Tue, 18 Apr 2017 15:48:15 -0500 Message-ID: <20170418204815.9001-1-grygorii.strashko@ti.com> X-Mailer: git-send-email 2.10.1 MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The below backtrace can be observed on -rt kernel with CONFIG_DEBUG_RODATA option enabled: BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:993 in_atomic(): 1, irqs_disabled(): 128, pid: 14, name: migration/0 1 lock held by migration/0/14: #0: (tasklist_lock){+.+...}, at: [] update_sections_early+0x24/0xdc irq event stamp: 38 hardirqs last enabled at (37): [] _raw_spin_unlock_irq+0x24/0x68 hardirqs last disabled at (38): [] multi_cpu_stop+0xd8/0x138 softirqs last enabled at (0): [] copy_process.part.5+0x238/0x1b64 softirqs last disabled at (0): [< (null)>] (null) Preemption disabled at: [] cpu_stopper_thread+0x80/0x10c CPU: 0 PID: 14 Comm: migration/0 Not tainted 4.9.21-rt16-02220-g49e319c #15 Hardware name: Generic DRA74X (Flattened Device Tree) [] (unwind_backtrace) from [] (show_stack+0x10/0x14) [] (show_stack) from [] (dump_stack+0xa8/0xd4) [] (dump_stack) from [] (___might_sleep+0x1bc/0x2ac) [] (___might_sleep) from [] (__rt_spin_lock+0x1c/0x30) [] (__rt_spin_lock) from [] (rt_read_lock+0x54/0x68) [] (rt_read_lock) from [] (update_sections_early+0x24/0xdc) [] (update_sections_early) from [] (__fix_kernmem_perms+0x10/0x1c) [] (__fix_kernmem_perms) from [] (multi_cpu_stop+0x100/0x138) [] (multi_cpu_stop) from [] (cpu_stopper_thread+0x88/0x10c) [] (cpu_stopper_thread) from [] (smpboot_thread_fn+0x174/0x31c) [] (smpboot_thread_fn) from [] (kthread+0xf0/0x108) [] (kthread) from [] (ret_from_fork+0x14/0x3c) Freeing unused kernel memory: 1024K (c0d00000 - c0e00000) The stop_machine() is called with cpus = NULL from fix_kernmem_perms() and mark_rodata_ro() which means only one CPU will execute update_sections_early() while all other CPUs will spin and wait. Hence, it's safe to remove tasklist locking from update_sections_early(). As part of this change also mark functions which are local to this module as static to simplify code analize in the future. Cc: Kees Cook Cc: Laura Abbott Signed-off-by: Grygorii Strashko --- arch/arm/mm/init.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index 370581a..a77953a 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -693,30 +693,28 @@ static void update_sections_early(struct section_perm perms[], int n) { struct task_struct *t, *s; - read_lock(&tasklist_lock); for_each_process(t) { if (t->flags & PF_KTHREAD) continue; for_each_thread(t, s) set_section_perms(perms, n, true, s->mm); } - read_unlock(&tasklist_lock); set_section_perms(perms, n, true, current->active_mm); set_section_perms(perms, n, true, &init_mm); } -int __fix_kernmem_perms(void *unused) +static int __fix_kernmem_perms(void *unused) { update_sections_early(nx_perms, ARRAY_SIZE(nx_perms)); return 0; } -void fix_kernmem_perms(void) +static void fix_kernmem_perms(void) { stop_machine(__fix_kernmem_perms, NULL, NULL); } -int __mark_rodata_ro(void *unused) +static int __mark_rodata_ro(void *unused) { update_sections_early(ro_perms, ARRAY_SIZE(ro_perms)); return 0; -- 2.10.1