Re: [PATCH V6 3/6] mm: Introduce VM_LOCKONFAULT

[Thierry Reding]

On Wed, Jul 29, 2015 at 11:42:52AM -0400, Eric B Munson wrote:
[...]
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index ca1e091..38d69fc 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -579,6 +579,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>  #ifdef CONFIG_X86_INTEL_MPX
>  		[ilog2(VM_MPX)]		= "mp",
>  #endif
> +		[ilog2(VM_LOCKONFAULT)]	= "lf",
>  		[ilog2(VM_LOCKED)]	= "lo",
>  		[ilog2(VM_IO)]		= "io",
>  		[ilog2(VM_SEQ_READ)]	= "sr",
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 2e872f9..c2f3551 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -127,6 +127,7 @@ extern unsigned int kobjsize(const void *objp);
>  #define VM_PFNMAP	0x00000400	/* Page-ranges managed without "struct page", just pure PFN */
>  #define VM_DENYWRITE	0x00000800	/* ETXTBSY on write attempts.. */
>  
> +#define VM_LOCKONFAULT	0x00001000	/* Lock the pages covered when they are faulted in */
>  #define VM_LOCKED	0x00002000
>  #define VM_IO           0x00004000	/* Memory mapped I/O or similar */
>  

This clashes with another change currently in linux-next:

	81d056997385 userfaultfd: add VM_UFFD_MISSING and VM_UFFD_WP

Adding Andrea for visibility.

I noticed this because I was trying to make selftests/vm/mlock2-tests
work to see if the new mlock2 syscall would work on ARM. It didn't, so I
had to investigate and noticed that two symbolic names resolve to the
same value, which results in the mnemonics table (first hunk above)
overwriting the VM_LOCKONFAULT entry with the VM_UFFD_WP entry.

I've applied the following patch locally to fix this up.

Andrew, I think both of those patches came in via your tree, so perhaps
the best thing would be to squash the below (provided everybody agrees
that it's the right fix) into Eric's patch, adding the VM_LOCKONFAULT
flag?

Thierry

---- >8 ----
From a0003ebfeb15f91094d17961633cabb4e1beed21 Mon Sep 17 00:00:00 2001
From: Thierry Reding <treding@xxxxxxxxxx>
Date: Fri, 7 Aug 2015 14:23:42 +0200
Subject: [PATCH] mm: Fix VM_LOCKONFAULT clash with VM_UFFD_WP

Currently two patches in linux-next add new VM flags and unfortunately
two flags end up using the same value. This results for example in the
/proc/pid/smaps file not listing the VM_LOCKONFAULT flag, which breaks
tools/testing/selftests/vm/mlock2-tests.

Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
 fs/proc/task_mmu.c | 2 +-
 include/linux/mm.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index bdd7e48a85f0..893e4b9bb2da 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -592,13 +592,13 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 #ifdef CONFIG_X86_INTEL_MPX
 		[ilog2(VM_MPX)]		= "mp",
 #endif
-		[ilog2(VM_LOCKONFAULT)]	= "lf",
 		[ilog2(VM_LOCKED)]	= "lo",
 		[ilog2(VM_IO)]		= "io",
 		[ilog2(VM_SEQ_READ)]	= "sr",
 		[ilog2(VM_RAND_READ)]	= "rr",
 		[ilog2(VM_DONTCOPY)]	= "dc",
 		[ilog2(VM_DONTEXPAND)]	= "de",
+		[ilog2(VM_LOCKONFAULT)]	= "lf",
 		[ilog2(VM_ACCOUNT)]	= "ac",
 		[ilog2(VM_NORESERVE)]	= "nr",
 		[ilog2(VM_HUGETLB)]	= "ht",
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 363ea2cda35f..cb4e1737d669 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -129,7 +129,6 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_DENYWRITE	0x00000800	/* ETXTBSY on write attempts.. */
 #define VM_UFFD_WP	0x00001000	/* wrprotect pages tracking */
 
-#define VM_LOCKONFAULT	0x00001000	/* Lock the pages covered when they are faulted in */
 #define VM_LOCKED	0x00002000
 #define VM_IO           0x00004000	/* Memory mapped I/O or similar */
 
@@ -139,6 +138,7 @@ extern unsigned int kobjsize(const void *objp);
 
 #define VM_DONTCOPY	0x00020000      /* Do not copy this vma on fork */
 #define VM_DONTEXPAND	0x00040000	/* Cannot expand with mremap() */
+#define VM_LOCKONFAULT	0x00080000	/* Lock the pages covered when they are faulted in */
 #define VM_ACCOUNT	0x00100000	/* Is a VM accounted object */
 #define VM_NORESERVE	0x00200000	/* should the VM suppress accounting */
 #define VM_HUGETLB	0x00400000	/* Huge TLB Page VM */
-- 
2.4.5

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