mm: enable RLIMIT_DATA by default with workaround for valgrind

Since commit 84638335900f ("mm: rework virtual memory accounting")
RLIMIT_DATA limits both brk() and private mmap() but this's disabled by
default because of incompatibility with older versions of valgrind.

Valgrind always set limit to zero and fails if RLIMIT_DATA is enabled.
Fortunately it changes only rlim_cur and keeps rlim_max for reverting
limit back when needed.

This patch checks current usage also against rlim_max if rlim_cur is
zero.  This is safe because task anyway can increase rlim_cur up to
rlim_max.  Size of brk is still checked against rlim_cur, so this part
is completely compatible - zero rlim_cur forbids brk() but allows
private mmap().

Link: http://lkml.kernel.org/r/56A28613.5070104@de.ibm.com
Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -66,7 +66,7 @@ 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;
+static bool ignore_rlimit_data;
 core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644);
 
 static void unmap_region(struct mm_struct *mm,
@@ -2886,13 +2886,17 @@ bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
 
 	if (is_data_mapping(flags) &&
 	    mm->data_vm + npages > rlimit(RLIMIT_DATA) >> PAGE_SHIFT) {
-		if (ignore_rlimit_data)
-			pr_warn_once("%s (%d): VmData %lu exceed data ulimit %lu. Will be forbidden soon.\n",
+		/* Workaround for Valgrind */
+		if (rlimit(RLIMIT_DATA) == 0 &&
+		    mm->data_vm + npages <= rlimit_max(RLIMIT_DATA) >> PAGE_SHIFT)
+			return true;
+		if (!ignore_rlimit_data) {
+			pr_warn_once("%s (%d): VmData %lu exceed data ulimit %lu. Update limits or use boot option ignore_rlimit_data.\n",
 				     current->comm, current->pid,
 				     (mm->data_vm + npages) << PAGE_SHIFT,
 				     rlimit(RLIMIT_DATA));
-		else
 			return false;
+		}
 	}
 
 	return true;