From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f199.google.com (mail-pf1-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id F17978E0001 for ; Tue, 18 Dec 2018 13:54:14 -0500 (EST) Received: by mail-pf1-f199.google.com with SMTP id b17so15941726pfc.11 for ; Tue, 18 Dec 2018 10:54:14 -0800 (PST) Received: from smtprelay.synopsys.com (smtprelay.synopsys.com. [198.182.60.111]) by mx.google.com with ESMTPS id z20si13629875pgv.159.2018.12.18.10.54.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 18 Dec 2018 10:54:13 -0800 (PST) From: Vineet Gupta Subject: [PATCH 1/2] ARC: show_regs: avoid page allocator Date: Tue, 18 Dec 2018 10:53:58 -0800 Message-ID: <1545159239-30628-2-git-send-email-vgupta@synopsys.com> In-Reply-To: <1545159239-30628-1-git-send-email-vgupta@synopsys.com> References: <1545159239-30628-1-git-send-email-vgupta@synopsys.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: linux-snps-arc@lists.infradead.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Peter Zijlstra , Vineet Gupta Use on-stack smaller buffers instead of dynamic pages. The motivation for this change was to address lockdep splat when signal handling code calls show_regs (with preemption disabled) and ARC show_regs calls into sleepable page allocator. | potentially unexpected fatal signal 11. | BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317 | in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv | no locks held by segv/57. | Preemption disabled at: | [<8182f17e>] get_signal+0x4a6/0x7c4 | CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23 | | Stack Trace: | arc_unwind_core.constprop.1+0xd0/0xf4 | __might_sleep+0x1f6/0x234 | __get_free_pages+0x174/0xca0 | show_regs+0x22/0x330 | get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable() | do_signal+0x30/0x224 | resume_user_mode_begin+0x90/0xd8 Despite this, lockdep still barfs (see next change), but this patch still has merit as in we use smaller/localized buffers now and there's less instructoh trace to sift thru when debugging pesky issues. Signed-off-by: Vineet Gupta --- arch/arc/kernel/troubleshoot.c | 22 +++++++++------------- 1 file changed, 9 insertions(+), 13 deletions(-) diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c index e8d9fb452346..2885bec71fb8 100644 --- a/arch/arc/kernel/troubleshoot.c +++ b/arch/arc/kernel/troubleshoot.c @@ -58,11 +58,12 @@ static void show_callee_regs(struct callee_regs *cregs) print_reg_file(&(cregs->r13), 13); } -static void print_task_path_n_nm(struct task_struct *tsk, char *buf) +static void print_task_path_n_nm(struct task_struct *tsk) { char *path_nm = NULL; struct mm_struct *mm; struct file *exe_file; + char buf[256]; mm = get_task_mm(tsk); if (!mm) @@ -80,10 +81,9 @@ static void print_task_path_n_nm(struct task_struct *tsk, char *buf) pr_info("Path: %s\n", !IS_ERR(path_nm) ? path_nm : "?"); } -static void show_faulting_vma(unsigned long address, char *buf) +static void show_faulting_vma(unsigned long address) { struct vm_area_struct *vma; - char *nm = buf; struct mm_struct *active_mm = current->active_mm; /* can't use print_vma_addr() yet as it doesn't check for @@ -96,8 +96,11 @@ static void show_faulting_vma(unsigned long address, char *buf) * if the container VMA is not found */ if (vma && (vma->vm_start <= address)) { + char buf[256]; + char *nm = "?"; + if (vma->vm_file) { - nm = file_path(vma->vm_file, buf, PAGE_SIZE - 1); + nm = file_path(vma->vm_file, buf, 256-1); if (IS_ERR(nm)) nm = "?"; } @@ -173,13 +176,8 @@ void show_regs(struct pt_regs *regs) { struct task_struct *tsk = current; struct callee_regs *cregs; - char *buf; - - buf = (char *)__get_free_page(GFP_KERNEL); - if (!buf) - return; - print_task_path_n_nm(tsk, buf); + print_task_path_n_nm(tsk); show_regs_print_info(KERN_INFO); show_ecr_verbose(regs); @@ -189,7 +187,7 @@ void show_regs(struct pt_regs *regs) (void *)regs->blink, (void *)regs->ret); if (user_mode(regs)) - show_faulting_vma(regs->ret, buf); /* faulting code, not data */ + show_faulting_vma(regs->ret); /* faulting code, not data */ pr_info("[STAT32]: 0x%08lx", regs->status32); @@ -221,8 +219,6 @@ void show_regs(struct pt_regs *regs) cregs = (struct callee_regs *)current->thread.callee_reg; if (cregs) show_callee_regs(cregs); - - free_page((unsigned long)buf); } void show_kernel_fault_diag(const char *str, struct pt_regs *regs, -- 2.7.4