AGP fix race condition between unmapping and freeing pages

With Andi's clflush fixup, we were getting hangs on server exit, flushing the
mappings after freeing each page helped.

This showed up a race condition where the pages after being freed could be
reused before the agp mappings had been flushed.  Flushing after each single
page is a bad thing for future drm work, so make the page destroy a two pass
unmapping all the pages, flushing the mappings, and then destroying the pages.

Signed-off-by: Dave Airlie <airlied@linux.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 16 insertions, 11 deletions

diff --git a/drivers/char/agp/ali-agp.c b/drivers/char/agp/ali-agp.c
index 4941ddb78939..aa5ddb716ffb 100644
--- a/drivers/char/agp/ali-agp.c
+++ b/drivers/char/agp/ali-agp.c
@@ -156,29 +156,34 @@ static void *m1541_alloc_page(struct agp_bridge_data *bridge)
         return addr;
 }
 
-static void ali_destroy_page(void * addr)
+static void ali_destroy_page(void * addr, int flags)
 {
         if (addr) {
-                global_cache_flush();   /* is this really needed?  --hch */
-                agp_generic_destroy_page(addr);
-                global_flush_tlb();
+                if (flags & AGP_PAGE_DESTROY_UNMAP) {
+                        global_cache_flush();   /* is this really needed?  --hch */
+                        agp_generic_destroy_page(addr, flags);
+                        global_flush_tlb();
+                } else
+                        agp_generic_destroy_page(addr, flags);
         }
 }
 
-static void m1541_destroy_page(void * addr)
+static void m1541_destroy_page(void * addr, int flags)
 {
         u32 temp;
 
         if (addr == NULL)
                 return;
 
-        global_cache_flush();
+        if (flags & AGP_PAGE_DESTROY_UNMAP) {
+                global_cache_flush();
 
-        pci_read_config_dword(agp_bridge->dev, ALI_CACHE_FLUSH_CTRL, &temp);
-        pci_write_config_dword(agp_bridge->dev, ALI_CACHE_FLUSH_CTRL,
-                        (((temp & ALI_CACHE_FLUSH_ADDR_MASK) |
-                          virt_to_gart(addr)) | ALI_CACHE_FLUSH_EN));
-        agp_generic_destroy_page(addr);
+                pci_read_config_dword(agp_bridge->dev, ALI_CACHE_FLUSH_CTRL, &temp);
+                pci_write_config_dword(agp_bridge->dev, ALI_CACHE_FLUSH_CTRL,
+                                       (((temp & ALI_CACHE_FLUSH_ADDR_MASK) |
+                                         virt_to_gart(addr)) | ALI_CACHE_FLUSH_EN));
+        }
+        agp_generic_destroy_page(addr, flags);
 }