[PATCH] fix low-memory BUG in slab

cache_grow() will call kmem_freepages() if the call to alloc_slabmgmt()
fails.  But the pages have not been marked PageSlab at this stage, so
kmem_freepages() goes BUG.

It is more symmetrical to mark the pages as PageSlab in kmem_getpages().

The patch also prunes a bunch of incorrect comments.

(PageSlab doesn't actually do anything: its only value is as a debug check.
I think the LKCD patch uses it).

diff --git a/mm/slab.c b/mm/slab.c
index d26829eb67d949798e3b26d42c7ce52eddc6c8e7..6273e8acf54f62bef70fa880f8b7f79bba656b95 100644 (file)
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -793,42 +793,42 @@ int __init cpucache_init(void)
 
 __initcall(cpucache_init);
 
-/* Interface to system's page allocator. No need to hold the cache-lock.
+/*
+ * Interface to system's page allocator. No need to hold the cache-lock.
+ *
+ * If we requested dmaable memory, we will get it. Even if we
+ * did not request dmaable memory, we might get it, but that
+ * would be relatively rare and ignorable.
  */
-static inline void * kmem_getpages (kmem_cache_t *cachep, unsigned long flags)
+static inline void *kmem_getpages(kmem_cache_t *cachep, unsigned long flags)
 {
-       void    *addr;
+       void *addr;
 
-       /*
-        * If we requested dmaable memory, we will get it. Even if we
-        * did not request dmaable memory, we might get it, but that
-        * would be relatively rare and ignorable.
-        */
        flags |= cachep->gfpflags;
-       if ( cachep->flags & SLAB_RECLAIM_ACCOUNT) 
+       if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
                atomic_add(1<<cachep->gfporder, &slab_reclaim_pages);
-       addr = (void*) __get_free_pages(flags, cachep->gfporder);
-       /* Assume that now we have the pages no one else can legally
-        * messes with the 'struct page's.
-        * However vm_scan() might try to test the structure to see if
-        * it is a named-page or buffer-page.  The members it tests are
-        * of no interest here.....
-        */
+       addr = (void*)__get_free_pages(flags, cachep->gfporder);
+       if (addr) {
+               int i = (1 << cachep->gfporder);
+               struct page *page = virt_to_page(addr);
+
+               while (i--) {
+                       SetPageSlab(page);
+                       page++;
+               }
+       }
        return addr;
 }
 
-/* Interface to system's page release. */
-static inline void kmem_freepages (kmem_cache_t *cachep, void *addr)
+/*
+ * Interface to system's page release.
+ */
+static inline void kmem_freepages(kmem_cache_t *cachep, void *addr)
 {
        unsigned long i = (1<<cachep->gfporder);
        struct page *page = virt_to_page(addr);
        const unsigned long nr_freed = i;
 
-       /* free_pages() does not clear the type bit - we do that.
-        * The pages have been unlinked from their cache-slab,
-        * but their 'struct page's might be accessed in
-        * vm_scan(). Shouldn't be a worry.
-        */
        while (i--) {
                if (!TestClearPageSlab(page))
                        BUG();
@@ -1608,7 +1608,6 @@ static int cache_grow (kmem_cache_t * cachep, int flags)
        do {
                SET_PAGE_CACHE(page, cachep);
                SET_PAGE_SLAB(page, slabp);
-               SetPageSlab(page);
                inc_page_state(nr_slab);
                page++;
        } while (--i);