linux-kernel - [PATCH] fs/proc: smaps should avoid VM

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Message-Id: <E1UWva5-0005fY-Km@eag09.americas.sgi.com>
Date:	Mon, 29 Apr 2013 16:25:53 -0500
From:	Cliff Wickman <cpw@....com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, mgorman@...e.de, paul.mundt@...ia.com,
	dhowells@...hat.com, aarcange@...hat.com, hughd@...gle.com,
	gorcunov@...nvz.org, kamezawa.hiroyuki@...il.com,
	n-horiguchi@...jp.nec.com, eag0628@...il.com,
	khlebnikov@...nvz.org, sasha.levin@...cle.com,
	siddhesh.poyarekar@...il.com, rientjes@...gle.com,
	kirill.shutemov@...ux.intel.com, viro@...IV.linux.org.uk,
	amwang@...hat.com
Subject: [PATCH] fs/proc: smaps should avoid VM_PFNMAP areas


/proc/<pid>/smaps should not be looking at VM_PFNMAP areas.

Certain tests in show_smap() (especially for huge pages) assume that the
mapped PFN's are backed with page structures.  And this is not usually true
for VM_PFNMAP areas.  This can result in panics on kernel page faults when
attempting to address those page structures.

VM_PFNMAP areas are used by
- graphics memory manager   gpu/drm/drm_gem.c
- global reference unit     sgi-gru/grufile.c
- sgi special memory        char/mspec.c
- probably several out-of-tree modules

I'm copying everyone who has changed fs/proc/task_mmu.c recently, in case
of some reason to provide /proc/<pid>/smaps for these areas that I am not
aware of.

Signed-off-by: Cliff Wickman <cpw@....com>
---
 fs/proc/task_mmu.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux/fs/proc/task_mmu.c
===================================================================
--- linux.orig/fs/proc/task_mmu.c
+++ linux/fs/proc/task_mmu.c
@@ -589,6 +589,9 @@ static int show_smap(struct seq_file *m,
 		.private = &mss,
 	};
 
+	if (vma->vm_flags & VM_PFNMAP)
+		return 0;
+
 	memset(&mss, 0, sizeof mss);
 	mss.vma = vma;
 	/* mmap_sem is held in m_start */
--
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