[RFC 1/2] [RFC] mm: Account anon mappings as RLIMIT_DATA

[Cyrill Gorcunov]

When inspecting a vague code inside prctl(PR_SET_MM_MEM)
call (which testing the RLIMIT_DATA value to figure out
if we're allowed to assign new @start_brk, @brk, @start_data,
@end_data from mm_struct) it's been commited that RLIMIT_DATA
in a form it's implemented now doesn't do anything useful
because most of user-space libraries use mmap() syscall
for dynamic memory allocations.

So Linus suggested to convert RLIMIT_DATA rlimit into something
suitable for anonymous memory accounting. Here we introduce
new @anon_vm member into mm descriptor which is updated
on every vm_stat_account() call.

Tests for RLIMIT_DATA are done in three places:
 - mmap_region: when user calls mmap() helper
 - do_brk: for brk() helper
 - vma_to_resize: when mremap() is used

The do_brk() is also used in vm_brk() which is called
when the kernel loads Elf and aout files to execute.

Because test for limit is done in do_brk helper we
no longer need to call check_data_rlimit here.

v2:
 - update doc
 - add may_expand_anon_vm helper
 - call for RLIMIT_DATA test in mremap and do_brk

CC: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
CC: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Willy Tarreau <w@xxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxx>
CC: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
CC: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
CC: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
CC: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
---
 Documentation/filesystems/proc.txt |    1 
 fs/proc/task_mmu.c                 |    2 +
 include/linux/mm_types.h           |    1 
 mm/mmap.c                          |   46 ++++++++++++++++++++++---------------
 mm/mremap.c                        |    5 ++++
 5 files changed, 37 insertions(+), 18 deletions(-)

Index: linux-ml.git/Documentation/filesystems/proc.txt
===================================================================
--- linux-ml.git.orig/Documentation/filesystems/proc.txt
+++ linux-ml.git/Documentation/filesystems/proc.txt
@@ -233,6 +233,7 @@ Table 1-2: Contents of the status files
  VmHWM                       peak resident set size ("high water mark")
  VmRSS                       size of memory portions
  VmData                      size of data, stack, and text segments
+ VmAnon                      size of anonymous private memory (not file backended)
  VmStk                       size of data, stack, and text segments
  VmExe                       size of text segment
  VmLib                       size of shared library code
Index: linux-ml.git/fs/proc/task_mmu.c
===================================================================
--- linux-ml.git.orig/fs/proc/task_mmu.c
+++ linux-ml.git/fs/proc/task_mmu.c
@@ -53,6 +53,7 @@ void task_mem(struct seq_file *m, struct
 		"VmHWM:\t%8lu kB\n"
 		"VmRSS:\t%8lu kB\n"
 		"VmData:\t%8lu kB\n"
+		"VmAnon:\t%8lu kB\n"
 		"VmStk:\t%8lu kB\n"
 		"VmExe:\t%8lu kB\n"
 		"VmLib:\t%8lu kB\n"
@@ -66,6 +67,7 @@ void task_mem(struct seq_file *m, struct
 		hiwater_rss << (PAGE_SHIFT-10),
 		total_rss << (PAGE_SHIFT-10),
 		data << (PAGE_SHIFT-10),
+		mm->anon_vm << (PAGE_SHIFT-10),
 		mm->stack_vm << (PAGE_SHIFT-10), text, lib,
 		ptes >> 10,
 		pmds >> 10,
Index: linux-ml.git/include/linux/mm_types.h
===================================================================
--- linux-ml.git.orig/include/linux/mm_types.h
+++ linux-ml.git/include/linux/mm_types.h
@@ -429,6 +429,7 @@ struct mm_struct {
 	unsigned long shared_vm;	/* Shared pages (files) */
 	unsigned long exec_vm;		/* VM_EXEC & ~VM_WRITE */
 	unsigned long stack_vm;		/* VM_GROWSUP/DOWN */
+	unsigned long anon_vm;		/* Anonymous pages mapped */
 	unsigned long def_flags;
 	unsigned long start_code, end_code, start_data, end_data;
 	unsigned long start_brk, brk, start_stack;
Index: linux-ml.git/mm/mmap.c
===================================================================
--- linux-ml.git.orig/mm/mmap.c
+++ linux-ml.git/mm/mmap.c
@@ -309,16 +309,6 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
 	if (brk < min_brk)
 		goto out;
 
-	/*
-	 * Check against rlimit here. If this check is done later after the test
-	 * of oldbrk with newbrk then it can escape the test and let the data
-	 * segment grow beyond its set limit the in case where the limit is
-	 * not page aligned -Ram Gupta
-	 */
-	if (check_data_rlimit(rlimit(RLIMIT_DATA), brk, mm->start_brk,
-			      mm->end_data, mm->start_data))
-		goto out;
-
 	newbrk = PAGE_ALIGN(brk);
 	oldbrk = PAGE_ALIGN(mm->brk);
 	if (oldbrk == newbrk)
@@ -1223,6 +1213,9 @@ void vm_stat_account(struct mm_struct *m
 			mm->exec_vm += pages;
 	} else if (flags & stack_flags)
 		mm->stack_vm += pages;
+
+	if (anon_accountable_mapping(file, flags))
+		mm->anon_vm += pages;
 }
 #endif /* CONFIG_PROC_FS */
 
@@ -1578,6 +1571,14 @@ unsigned long mmap_region(struct file *f
 	}
 
 	/*
+	 * For anon mappings make sure we don't exceed the limit.
+	 */
+	if (anon_accountable_mapping(file, vm_flags)) {
+		if (!may_expand_anon_vm(mm, len >> PAGE_SHIFT))
+			return -ENOMEM;
+	}
+
+	/*
 	 * Can we just expand an old mapping?
 	 */
 	vma = vma_merge(mm, prev, addr, addr + len, vm_flags,
@@ -2760,7 +2761,8 @@ static unsigned long do_brk(unsigned lon
 	}
 
 	/* Check against address space limits *after* clearing old maps... */
-	if (!may_expand_vm(mm, len >> PAGE_SHIFT))
+	if (!may_expand_vm(mm, len >> PAGE_SHIFT) ||
+	    !may_expand_anon_vm(mm, len >> PAGE_SHIFT))
 		return -ENOMEM;
 
 	if (mm->map_count > sysctl_max_map_count)
@@ -2795,6 +2797,7 @@ static unsigned long do_brk(unsigned lon
 out:
 	perf_event_mmap(vma);
 	mm->total_vm += len >> PAGE_SHIFT;
+	mm->anon_vm += len >> PAGE_SHIFT;
 	if (flags & VM_LOCKED)
 		mm->locked_vm += (len >> PAGE_SHIFT);
 	vma->vm_flags |= VM_SOFTDIRTY;
@@ -2982,20 +2985,27 @@ out:
 	return NULL;
 }
 
+static inline int __may_expand_vm(unsigned int limit,
+				  unsigned long cur,
+				  unsigned long npages)
+{
+	unsigned long lim = rlimit(limit) >> PAGE_SHIFT;
+
+	return ((cur + npages) > lim) ? 0 : 1;
+}
+
 /*
  * Return true if the calling process may expand its vm space by the passed
  * number of pages
  */
 int may_expand_vm(struct mm_struct *mm, unsigned long npages)
 {
-	unsigned long cur = mm->total_vm;	/* pages */
-	unsigned long lim;
-
-	lim = rlimit(RLIMIT_AS) >> PAGE_SHIFT;
+	return __may_expand_vm(RLIMIT_AS, mm->total_vm, npages);
+}
 
-	if (cur + npages > lim)
-		return 0;
-	return 1;
+int may_expand_anon_vm(struct mm_struct *mm, unsigned long npages)
+{
+	return __may_expand_vm(RLIMIT_DATA, mm->anon_vm, npages);
 }
 
 static int special_mapping_fault(struct vm_area_struct *vma,
Index: linux-ml.git/mm/mremap.c
===================================================================
--- linux-ml.git.orig/mm/mremap.c
+++ linux-ml.git/mm/mremap.c
@@ -382,6 +382,11 @@ static struct vm_area_struct *vma_to_res
 	if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
 		return ERR_PTR(-ENOMEM);
 
+	if (anon_accountable_mapping(vma->vm_file, vma->vm_flags)) {
+		if (!may_expand_anon_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
+			return ERR_PTR(-ENOMEM);
+	}
+
 	if (vma->vm_flags & VM_ACCOUNT) {
 		unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 		if (security_vm_enough_memory_mm(mm, charged))

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