3 files changed, 47 insertions, 3 deletions

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index f462439cc288..bd91987c065f 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -105,6 +105,8 @@ extern int vm_highmem_is_dirtyable;
 extern int block_dump;
 extern int laptop_mode;
 
+extern unsigned long determine_dirtyable_memory(void);
+
 extern int dirty_ratio_handler(struct ctl_table *table, int write,
                 struct file *filp, void __user *buffer, size_t *lenp,
                 loff_t *ppos);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 82ced406aacf..2824cf48cdca 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -27,6 +27,7 @@
 #include <linux/poll.h>
 #include <linux/gfp.h>
 #include <linux/fs.h>
+#include <linux/writeback.h>
 
 #include <linux/stacktrace.h>
 
@@ -51,6 +52,8 @@ static int trace_free_page(void);
 
 static int tracing_disabled = 1;
 
+static unsigned long tracing_pages_allocated;
+
 long
 ns2usecs(cycle_t nsec)
 {
@@ -2591,12 +2594,41 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
         }
 
         if (val > global_trace.entries) {
+                long pages_requested;
+                unsigned long freeable_pages;
+
+                /* make sure we have enough memory before mapping */
+                pages_requested =
+                        (val + (ENTRIES_PER_PAGE-1)) / ENTRIES_PER_PAGE;
+
+                /* account for each buffer (and max_tr) */
+                pages_requested *= tracing_nr_buffers * 2;
+
+                /* Check for overflow */
+                if (pages_requested < 0) {
+                        cnt = -ENOMEM;
+                        goto out;
+                }
+
+                freeable_pages = determine_dirtyable_memory();
+
+                /* we only allow to request 1/4 of useable memory */
+                if (pages_requested >
+                    ((freeable_pages + tracing_pages_allocated) / 4)) {
+                        cnt = -ENOMEM;
+                        goto out;
+                }
+
                 while (global_trace.entries < val) {
                         if (trace_alloc_page()) {
                                 cnt = -ENOMEM;
                                 goto out;
                         }
+                        /* double check that we don't go over the known pages */
+                        if (tracing_pages_allocated > pages_requested)
+                                break;
                 }
+
         } else {
                 /* include the number of entries in val (inc of page entries) */
                 while (global_trace.entries > val + (ENTRIES_PER_PAGE - 1))
@@ -2776,6 +2808,7 @@ static int trace_alloc_page(void)
         struct page *page, *tmp;
         LIST_HEAD(pages);
         void *array;
+        unsigned pages_allocated = 0;
         int i;
 
         /* first allocate a page for each CPU */
@@ -2787,6 +2820,7 @@ static int trace_alloc_page(void)
                         goto free_pages;
                 }
 
+                pages_allocated++;
                 page = virt_to_page(array);
                 list_add(&page->lru, &pages);
 
@@ -2798,6 +2832,7 @@ static int trace_alloc_page(void)
                                "for trace buffer!\n");
                         goto free_pages;
                 }
+                pages_allocated++;
                 page = virt_to_page(array);
                 list_add(&page->lru, &pages);
 #endif
@@ -2819,6 +2854,7 @@ static int trace_alloc_page(void)
                 SetPageLRU(page);
 #endif
         }
+        tracing_pages_allocated += pages_allocated;
         global_trace.entries += ENTRIES_PER_PAGE;
 
         return 0;
@@ -2853,6 +2889,8 @@ static int trace_free_page(void)
                 page = list_entry(p, struct page, lru);
                 ClearPageLRU(page);
                 list_del(&page->lru);
+                tracing_pages_allocated--;
+                tracing_pages_allocated--;
                 __free_page(page);
 
                 tracing_reset(data);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 789b6adbef37..b38f700825fc 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -126,8 +126,6 @@ static void background_writeout(unsigned long _min_pages);
 static struct prop_descriptor vm_completions;
 static struct prop_descriptor vm_dirties;
 
-static unsigned long determine_dirtyable_memory(void);
-
 /*
  * couple the period to the dirty_ratio:
  *
@@ -347,7 +345,13 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
 #endif
 }
 
-static unsigned long determine_dirtyable_memory(void)
+/**
+ * determine_dirtyable_memory - amount of memory that may be used
+ *
+ * Returns the numebr of pages that can currently be freed and used
+ * by the kernel for direct mappings.
+ */
+unsigned long determine_dirtyable_memory(void)
 {
         unsigned long x;