[PATCH v2] mm: warn about VmData over RLIMIT_DATA

[Konstantin Khlebnikov]

This patch fixes 84638335900f ("mm: rework virtual memory accounting")

Before that commit RLIMIT_DATA have control only over size of the brk region.
But that change have caused problems with all existing versions of valgrind,
because it set RLIMIT_DATA to zero.

This patch fixes RLIMIT_DATA check (limit actually in bytes, not pages)
and by default turns it into warning which prints at first VmData misuse.
Like: "VmData 516096 exceeds RLIMIT_DATA 512000"

Behavior is controlled by boot param ignore_rlimit_data=y/n and by sysfs
/sys/module/kernel/parameters/ignore_rlimit_data. For now it set to "y".

Signed-off-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20151228211015.GL2194@uranus
Reported-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
 Documentation/kernel-parameters.txt |    5 +++++
 mm/mmap.c                           |   12 +++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index cfb2c0f1a4a8..d728caf7aa52 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1461,6 +1461,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			could change it dynamically, usually by
 			/sys/module/printk/parameters/ignore_loglevel.
 
+	ignore_rlimit_data
+			Ignore RLIMIT_DATA setting for private mappings,
+			print warning at first misuse. Could be changed by
+			/sys/module/kernel/parameters/ignore_rlimit_data.
+
 	ihash_entries=	[KNL]
 			Set number of hash buckets for inode cache.
 
diff --git a/mm/mmap.c b/mm/mmap.c
index 84b12624ceb0..46d2ed6cb0df 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -42,6 +42,7 @@
 #include <linux/memory.h>
 #include <linux/printk.h>
 #include <linux/userfaultfd_k.h>
+#include <linux/moduleparam.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -69,6 +70,8 @@ const int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
 int mmap_rnd_compat_bits __read_mostly = CONFIG_ARCH_MMAP_RND_COMPAT_BITS;
 #endif
 
+static bool ignore_rlimit_data = true;
+core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644);
 
 static void unmap_region(struct mm_struct *mm,
 		struct vm_area_struct *vma, struct vm_area_struct *prev,
@@ -2982,9 +2985,12 @@ bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
 	if (mm->total_vm + npages > rlimit(RLIMIT_AS) >> PAGE_SHIFT)
 		return false;
 
-	if ((flags & (VM_WRITE | VM_SHARED | (VM_STACK_FLAGS &
-				(VM_GROWSUP | VM_GROWSDOWN)))) == VM_WRITE)
-		return mm->data_vm + npages <= rlimit(RLIMIT_DATA);
+	if ((flags & (VM_WRITE | VM_SHARED |
+		(VM_STACK_FLAGS & (VM_GROWSUP | VM_GROWSDOWN)))) == VM_WRITE &&
+	    mm->data_vm + npages > rlimit(RLIMIT_DATA) >> PAGE_SHIFT &&
+	    !WARN_ONCE(ignore_rlimit_data, "VmData %lu exceeds RLIMIT_DATA %lu",
+		       (mm->data_vm + npages)<<PAGE_SHIFT, rlimit(RLIMIT_DATA)))
+		return false;
 
 	return true;
 }