[PATCH] fs/proc: smaps should avoid VM_PFNMAP areas

[Cliff Wickman <cpw@sgi.com>]

/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@sgi.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 */