Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932115Ab2JSIgF (ORCPT ); Fri, 19 Oct 2012 04:36:05 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:46452 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757736Ab2JSIgB (ORCPT ); Fri, 19 Oct 2012 04:36:01 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.8.4 Message-ID: <508110C4.6030805@jp.fujitsu.com> Date: Fri, 19 Oct 2012 17:35:16 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:16.0) Gecko/20121010 Thunderbird/16.0.1 MIME-Version: 1.0 To: David Rientjes CC: Linus Torvalds , Andrew Morton , Dave Jones , KOSAKI Motohiro , bhutchings@solarflare.com, Konstantin Khlebnikov , Naoya Horiguchi , Hugh Dickins , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [patch for-3.7 v3] mm, mempolicy: hold task->mempolicy refcount while reading numa_maps. References:

<20121017040515.GA13505@redhat.com> <20121017181413.GA16805@redhat.com> <20121017193229.GC16805@redhat.com> <20121017194501.GA24400@redhat.com> <507F803A.8000900@jp.fujitsu.com> <507F86BD.7070201@jp.fujitsu.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5693 Lines: 176 (2012/10/19 5:03), David Rientjes wrote: > On Thu, 18 Oct 2012, Kamezawa Hiroyuki wrote: >> @@ -132,7 +162,7 @@ static void *m_start(struct seq_file *m, loff_t *pos) >> tail_vma = get_gate_vma(priv->task->mm); >> priv->tail_vma = tail_vma; >> - >> + hold_task_mempolicy(priv); >> /* Start with last addr hint */ >> vma = find_vma(mm, last_addr); >> if (last_addr && vma) { >> @@ -159,6 +189,7 @@ out: >> if (vma) >> return vma; >> + release_task_mempolicy(priv); >> /* End of vmas has been reached */ >> m->version = (tail_vma != NULL)? 0: -1UL; >> up_read(&mm->mmap_sem); > > Otherwise looks good, but please remove the two task_lock()'s in > show_numa_map() that I added as part of this since you're replacing the > need for locking. > Thank you for your review. How about this ? == From c5849c9034abeec3f26bf30dadccd393b0c5c25e Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Fri, 19 Oct 2012 17:00:55 +0900 Subject: [PATCH] hold task->mempolicy while numa_maps scans. /proc//numa_maps scans vma and show mempolicy under mmap_sem. It sometimes accesses task->mempolicy which can be freed without mmap_sem and numa_maps can show some garbage while scanning. This patch tries to take reference count of task->mempolicy at reading numa_maps before calling get_vma_policy(). By this, task->mempolicy will not be freed until numa_maps reaches its end. Signed-off-by: KAMEZAWA Hiroyuki V2->v3 - updated comments to be more verbose. - removed task_lock() in numa_maps code. V1->V2 - access task->mempolicy only once and remember it. Becase kernel/exit.c can overwrite it. Signed-off-by: KAMEZAWA Hiroyuki --- fs/proc/internal.h | 4 ++++ fs/proc/task_mmu.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 50 insertions(+), 3 deletions(-) diff --git a/fs/proc/internal.h b/fs/proc/internal.h index cceaab0..43973b0 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -12,6 +12,7 @@ #include #include struct ctl_table_header; +struct mempolicy; extern struct proc_dir_entry proc_root; #ifdef CONFIG_PROC_SYSCTL @@ -74,6 +75,9 @@ struct proc_maps_private { #ifdef CONFIG_MMU struct vm_area_struct *tail_vma; #endif +#ifdef CONFIG_NUMA + struct mempolicy *task_mempolicy; +#endif }; void proc_init_inodecache(void); diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 14df880..2371fea 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -89,11 +89,55 @@ static void pad_len_spaces(struct seq_file *m, int len) len = 1; seq_printf(m, "%*c", len, ' '); } +#ifdef CONFIG_NUMA +/* + * These functions are for numa_maps but called in generic **maps seq_file + * ->start(), ->stop() ops. + * + * numa_maps scans all vmas under mmap_sem and checks their mempolicy. + * Each mempolicy object is controlled by reference counting. The problem here + * is how to avoid accessing dead mempolicy object. + * + * Because we're holding mmap_sem while reading seq_file, it's safe to access + * each vma's mempolicy, no vma objects will never drop refs to mempolicy. + * + * A task's mempolicy (task->mempolicy) has different behavior. task->mempolicy + * is set and replaced under mmap_sem but unrefed and cleared under task_lock(). + * So, without task_lock(), we cannot trust get_vma_policy() because we cannot + * gurantee the task never exits under us. But taking task_lock() around + * get_vma_plicy() causes lock order problem. + * + * To access task->mempolicy without lock, we hold a reference count of an + * object pointed by task->mempolicy and remember it. This will guarantee + * that task->mempolicy points to an alive object or NULL in numa_maps accesses. + */ +static void hold_task_mempolicy(struct proc_maps_private *priv) +{ + struct task_struct *task = priv->task; + + task_lock(task); + priv->task_mempolicy = task->mempolicy; + mpol_get(priv->task_mempolicy); + task_unlock(task); +} +static void release_task_mempolicy(struct proc_maps_private *priv) +{ + mpol_put(priv->task_mempolicy); +} +#else +static void hold_task_mempolicy(struct proc_maps_private *priv) +{ +} +static void release_task_mempolicy(struct proc_maps_private *priv) +{ +} +#endif static void vma_stop(struct proc_maps_private *priv, struct vm_area_struct *vma) { if (vma && vma != priv->tail_vma) { struct mm_struct *mm = vma->vm_mm; + release_task_mempolicy(priv); up_read(&mm->mmap_sem); mmput(mm); } @@ -132,7 +176,7 @@ static void *m_start(struct seq_file *m, loff_t *pos) tail_vma = get_gate_vma(priv->task->mm); priv->tail_vma = tail_vma; - + hold_task_mempolicy(priv); /* Start with last addr hint */ vma = find_vma(mm, last_addr); if (last_addr && vma) { @@ -159,6 +203,7 @@ out: if (vma) return vma; + release_task_mempolicy(priv); /* End of vmas has been reached */ m->version = (tail_vma != NULL)? 0: -1UL; up_read(&mm->mmap_sem); @@ -1178,11 +1223,9 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid) walk.private = md; walk.mm = mm; - task_lock(task); pol = get_vma_policy(task, vma, vma->vm_start); mpol_to_str(buffer, sizeof(buffer), pol, 0); mpol_cond_put(pol); - task_unlock(task); seq_printf(m, "%08lx %s", vma->vm_start, buffer); -- 1.7.10.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/