Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751811Ab2JREel (ORCPT ); Thu, 18 Oct 2012 00:34:41 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:52669 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298Ab2JREek (ORCPT ); Thu, 18 Oct 2012 00:34:40 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.8.4 Message-ID: <507F86BD.7070201@jp.fujitsu.com> Date: Thu, 18 Oct 2012 13:34:05 +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: Re: [patch for-3.7 v2] mm, mempolicy: avoid taking mutex inside spinlock when 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> In-Reply-To: <507F803A.8000900@jp.fujitsu.com> 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: 5827 Lines: 169 (2012/10/18 13:06), Kamezawa Hiroyuki wrote: > (2012/10/18 6:31), David Rientjes wrote: >> As a result of commit 32f8516a8c73 ("mm, mempolicy: fix printing stack >> contents in numa_maps"), the mutex protecting a shared policy can be >> inadvertently taken while holding task_lock(task). >> >> Recently, commit b22d127a39dd ("mempolicy: fix a race in >> shared_policy_replace()") switched the spinlock within a shared policy to >> a mutex so sp_alloc() could block. Thus, a refcount must be grabbed on >> all mempolicies returned by get_vma_policy() so it isn't freed while being >> passed to mpol_to_str() when reading /proc/pid/numa_maps. >> >> This patch only takes task_lock() while dereferencing task->mempolicy in >> get_vma_policy() if it's non-NULL in the lockess check to increment its >> refcount. This ensures it will remain in memory until dropped by >> __mpol_put() after mpol_to_str() is called. >> >> Refcounts of shared policies are grabbed by the ->get_policy() function of >> the vma, all others will be grabbed directly in get_vma_policy(). Now >> that this is done, all callers now unconditionally drop the refcount. >> > > please add original problem description.... > > from your 1st patch. >> When reading /proc/pid/numa_maps, it's possible to return the contents of >> the stack where the mempolicy string should be printed if the policy gets >> freed from beneath us. >> >> This happens because mpol_to_str() may return an error the >> stack-allocated buffer is then printed without ever being stored. > ..... > > Hmm, I've read the whole thread again...and, I'm sorry if I misunderstand something. > > I think Kosaki mentioned the commit 52cd3b0740. It avoids refcounting in get_vma_policy() > because it's called every time alloc_pages_vma() is called, at every page fault. > So, it seems he doesn't agree this fix because of performance concern on big NUMA, > > > Can't we have another way to fix ? like this ? too ugly ? > Again, I'm sorry if I misunderstand the points. > Sorry this patch itself may be buggy. please don't test.. I missed that kernel/exit.c sets task->mempolicy to be NULL. fixed one here. -- From 5581c71e68a7f50e52fd67cca00148911023f9f5 Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Thu, 18 Oct 2012 13:50:29 +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 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 | 33 ++++++++++++++++++++++++++++++++- 2 files changed, 36 insertions(+), 1 deletion(-) 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..624927d 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -89,11 +89,41 @@ static void pad_len_spaces(struct seq_file *m, int len) len = 1; seq_printf(m, "%*c", len, ' '); } +#ifdef CONFIG_NUMA +/* + * numa_maps scans all vmas under mmap_sem and checks their mempolicy. + * But task->mempolicy is not guarded by mmap_sem, it can be cleared/freed + * under task_lock() (see kernel/exit.c) replacement of it is guarded by + * mmap_sem. So, take referenceount under task_lock() before we start + * scanning and drop it when numa_maps reaches the end. + */ +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 +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); -- 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/