x86: make DEBUG_PAGEALLOC and CPA more robust

Use PF_MEMALLOC to prevent recursive calls in the DBEUG_PAGEALLOC
case. This makes the code simpler and more robust against allocation
failures.

This fixes the following fallback to non-mmconfig:

   http://lkml.org/lkml/2008/2/20/551
   http://bugzilla.kernel.org/show_bug.cgi?id=10083

Also, for DEBUG_PAGEALLOC=n reduce the pool size to one page.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 51 insertions, 33 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 464d8fc21ce6..14e48b5a94ba 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -44,6 +44,12 @@ static inline unsigned long highmap_end_pfn(void)
 
 #endif
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
+# define debug_pagealloc 1
+#else
+# define debug_pagealloc 0
+#endif
+
 static inline int
 within(unsigned long addr, unsigned long start, unsigned long end)
 {
@@ -355,45 +361,48 @@ out_unlock:
 
 static LIST_HEAD(page_pool);
 static unsigned long pool_size, pool_pages, pool_low;
-static unsigned long pool_used, pool_failed, pool_refill;
+static unsigned long pool_used, pool_failed;
 
-static void cpa_fill_pool(void)
+static void cpa_fill_pool(struct page **ret)
 {
-        struct page *p;
         gfp_t gfp = GFP_KERNEL;
+        unsigned long flags;
+        struct page *p;
 
-        /* Do not allocate from interrupt context */
-        if (in_irq() || irqs_disabled())
-                return;
         /*
-         * Check unlocked. I does not matter when we have one more
-         * page in the pool. The bit lock avoids recursive pool
-         * allocations:
+         * Avoid recursion (on debug-pagealloc) and also signal
+         * our priority to get to these pagetables:
          */
-        if (pool_pages >= pool_size || test_and_set_bit_lock(0, &pool_refill))
+        if (current->flags & PF_MEMALLOC)
                 return;
+        current->flags |= PF_MEMALLOC;
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
         /*
-         * We could do:
-         * gfp = in_atomic() ? GFP_ATOMIC : GFP_KERNEL;
-         * but this fails on !PREEMPT kernels
+         * Allocate atomically from atomic contexts:
          */
-        gfp =  GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
-#endif
+        if (in_atomic() || irqs_disabled() || debug_pagealloc)
+                gfp =  GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
 
-        while (pool_pages < pool_size) {
+        while (pool_pages < pool_size || (ret && !*ret)) {
                 p = alloc_pages(gfp, 0);
                 if (!p) {
                         pool_failed++;
                         break;
                 }
-                spin_lock_irq(&pgd_lock);
+                /*
+                 * If the call site needs a page right now, provide it:
+                 */
+                if (ret && !*ret) {
+                        *ret = p;
+                        continue;
+                }
+                spin_lock_irqsave(&pgd_lock, flags);
                 list_add(&p->lru, &page_pool);
                 pool_pages++;
-                spin_unlock_irq(&pgd_lock);
+                spin_unlock_irqrestore(&pgd_lock, flags);
         }
-        clear_bit_unlock(0, &pool_refill);
+
+        current->flags &= ~PF_MEMALLOC;
 }
 
 #define SHIFT_MB                (20 - PAGE_SHIFT)
@@ -414,11 +423,15 @@ void __init cpa_init(void)
          * GiB. Shift MiB to Gib and multiply the result by
          * POOL_PAGES_PER_GB:
          */
-        gb = ((si.totalram >> SHIFT_MB) + ROUND_MB_GB) >> SHIFT_MB_GB;
-        pool_size = POOL_PAGES_PER_GB * gb;
+        if (debug_pagealloc) {
+                gb = ((si.totalram >> SHIFT_MB) + ROUND_MB_GB) >> SHIFT_MB_GB;
+                pool_size = POOL_PAGES_PER_GB * gb;
+        } else {
+                pool_size = 1;
+        }
         pool_low = pool_size;
 
-        cpa_fill_pool();
+        cpa_fill_pool(NULL);
         printk(KERN_DEBUG
                "CPA: page pool initialized %lu of %lu pages preallocated\n",
                pool_pages, pool_size);
@@ -440,16 +453,20 @@ static int split_large_page(pte_t *kpte, unsigned long address)
         spin_lock_irqsave(&pgd_lock, flags);
         if (list_empty(&page_pool)) {
                 spin_unlock_irqrestore(&pgd_lock, flags);
-                return -ENOMEM;
+                base = NULL;
+                cpa_fill_pool(&base);
+                if (!base)
+                        return -ENOMEM;
+                spin_lock_irqsave(&pgd_lock, flags);
+        } else {
+                base = list_first_entry(&page_pool, struct page, lru);
+                list_del(&base->lru);
+                pool_pages--;
+
+                if (pool_pages < pool_low)
+                        pool_low = pool_pages;
         }
 
-        base = list_first_entry(&page_pool, struct page, lru);
-        list_del(&base->lru);
-        pool_pages--;
-
-        if (pool_pages < pool_low)
-                pool_low = pool_pages;
-
         /*
          * Check for races, another CPU might have split this page
          * up for us already:
@@ -734,7 +751,8 @@ static int change_page_attr_set_clr(unsigned long addr, int numpages,
                 cpa_flush_all(cache);
 
 out:
-        cpa_fill_pool();
+        cpa_fill_pool(NULL);
+
         return ret;
 }
 
@@ -897,7 +915,7 @@ void kernel_map_pages(struct page *page, int numpages, int enable)
          * Try to refill the page pool here. We can do this only after
          * the tlb flush.
          */
-        cpa_fill_pool();
+        cpa_fill_pool(NULL);
 }
 
 #ifdef CONFIG_HIBERNATION