From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754109Ab2DWHKX (ORCPT ); Mon, 23 Apr 2012 03:10:23 -0400 Received: from mail-ob0-f174.google.com ([209.85.214.174]:45494 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753938Ab2DWHKR (ORCPT ); Mon, 23 Apr 2012 03:10:17 -0400 Date: Mon, 23 Apr 2012 00:09:01 -0700 From: Anton Vorontsov To: Andrew Morton , Oleg Nesterov Cc: Russell King , Mike Frysinger , Benjamin Herrenschmidt , Richard Weinberger , Paul Mundt , Peter Zijlstra , KOSAKI Motohiro , John Stultz , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, uclinux-dist-devel@blackfin.uclinux.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, linaro-kernel@lists.linaro.org, patches@linaro.org, linux-mm@kvack.org Subject: [PATCH 5/9] blackfin: A couple of task->mm handling fixes Message-ID: <20120423070901.GE30752@lizard> References: <20120423070641.GA27702@lizard> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20120423070641.GA27702@lizard> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The patch fixes two problems: 1. Working with task->mm w/o getting mm or grabing the task lock is dangerous as ->mm might disappear (exit_mm() assigns NULL under task_lock(), so tasklist lock is not enough). We can't use get_task_mm()/mmput() pair as mmput() might sleep, so we have to take the task lock while handle its mm. 2. Checking for process->mm is not enough because process' main thread may exit or detach its mm via use_mm(), but other threads may still have a valid mm. To catch this we use find_lock_task_mm(), which walks up all threads and returns an appropriate task (with task lock held). Suggested-by: Oleg Nesterov Signed-off-by: Anton Vorontsov --- arch/blackfin/kernel/trace.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) diff --git a/arch/blackfin/kernel/trace.c b/arch/blackfin/kernel/trace.c index 44bbf2f..d08f0e3 100644 --- a/arch/blackfin/kernel/trace.c +++ b/arch/blackfin/kernel/trace.c @@ -10,6 +10,8 @@ #include #include #include +#include +#include #include #include #include @@ -28,7 +30,6 @@ void decode_address(char *buf, unsigned long address) struct task_struct *p; struct mm_struct *mm; unsigned long flags, offset; - unsigned char in_atomic = (bfin_read_IPEND() & 0x10) || in_atomic(); struct rb_node *n; #ifdef CONFIG_KALLSYMS @@ -114,15 +115,15 @@ void decode_address(char *buf, unsigned long address) */ write_lock_irqsave(&tasklist_lock, flags); for_each_process(p) { - mm = (in_atomic ? p->mm : get_task_mm(p)); - if (!mm) - continue; + struct task_struct *t; - if (!down_read_trylock(&mm->mmap_sem)) { - if (!in_atomic) - mmput(mm); + t = find_lock_task_mm(p); + if (!t) continue; - } + + mm = t->mm; + if (!down_read_trylock(&mm->mmap_sem)) + goto __continue; for (n = rb_first(&mm->mm_rb); n; n = rb_next(n)) { struct vm_area_struct *vma; @@ -131,7 +132,7 @@ void decode_address(char *buf, unsigned long address) if (address >= vma->vm_start && address < vma->vm_end) { char _tmpbuf[256]; - char *name = p->comm; + char *name = t->comm; struct file *file = vma->vm_file; if (file) { @@ -164,8 +165,7 @@ void decode_address(char *buf, unsigned long address) name, vma->vm_start, vma->vm_end); up_read(&mm->mmap_sem); - if (!in_atomic) - mmput(mm); + task_unlock(t); if (buf[0] == '\0') sprintf(buf, "[ %s ] dynamic memory", name); @@ -175,8 +175,8 @@ void decode_address(char *buf, unsigned long address) } up_read(&mm->mmap_sem); - if (!in_atomic) - mmput(mm); +__continue: + task_unlock(t); } /* -- 1.7.9.2