Re: X-freeze after clflush changes [Was: 2.6.23-rc6-mm1]

["Dave Airlie" <airlied@gmail.com>]

> The code is broken anyways. If you free pages without flushing
> them first some other innocent user allocating them will end up
> with possible uncached pages for some time.
>
> Does this simple patch help?
>

I've attached a more complicated patch that does a 2 stage effort to
unmapping and freeing pages. My kernel no longer hangs with this
patch...

Jiri can you confirm?

I'll look at the other issue separately..

Dave.

From 225696d75e7ec0bafbb47b935bd700e3fbeefbde Mon Sep 17 00:00:00 2001
From: Dave Airlie <airlied@redhat.com>
Date: Thu, 20 Sep 2007 11:30:41 +1000
Subject: [PATCH] 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>
---
 drivers/char/agp/agp.h       |    7 +++++--
 drivers/char/agp/ali-agp.c   |   29 +++++++++++++++++------------
 drivers/char/agp/backend.c   |   12 ++++++++----
 drivers/char/agp/generic.c   |   20 ++++++++++++++------
 drivers/char/agp/i460-agp.c  |    4 ++--
 drivers/char/agp/intel-agp.c |    6 ++++--
 6 files changed, 50 insertions(+), 28 deletions(-)

diff --git a/drivers/char/agp/agp.h b/drivers/char/agp/agp.h
index 8955e7f..b83824c 100644
--- a/drivers/char/agp/agp.h
+++ b/drivers/char/agp/agp.h
@@ -58,6 +58,9 @@ struct gatt_mask {
 	 * devices this will probably be ignored */
 };
 
+#define AGP_PAGE_DESTROY_UNMAP 1
+#define AGP_PAGE_DESTROY_FREE 2
+
 struct aper_size_info_8 {
 	int size;
 	int num_entries;
@@ -113,7 +116,7 @@ struct agp_bridge_driver {
 	struct agp_memory *(*alloc_by_type) (size_t, int);
 	void (*free_by_type)(struct agp_memory *);
 	void *(*agp_alloc_page)(struct agp_bridge_data *);
-	void (*agp_destroy_page)(void *);
+	void (*agp_destroy_page)(void *, int flags);
         int (*agp_type_to_mask_type) (struct agp_bridge_data *, int);
 };
 
@@ -267,7 +270,7 @@ int agp_generic_remove_memory(struct agp_memory *mem, off_t pg_start, int type);
 struct agp_memory *agp_generic_alloc_by_type(size_t page_count, int type);
 void agp_generic_free_by_type(struct agp_memory *curr);
 void *agp_generic_alloc_page(struct agp_bridge_data *bridge);
-void agp_generic_destroy_page(void *addr);
+void agp_generic_destroy_page(void *addr, int flags);
 void agp_free_key(int key);
 int agp_num_entries(void);
 u32 agp_collect_device_status(struct agp_bridge_data *bridge, u32 mode, u32 command);
diff --git a/drivers/char/agp/ali-agp.c b/drivers/char/agp/ali-agp.c
index 4941ddb..2b65155 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();
-
-	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);
+	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, flags);
 }
 
 
diff --git a/drivers/char/agp/backend.c b/drivers/char/agp/backend.c
index 1b47c89..832ded2 100644
--- a/drivers/char/agp/backend.c
+++ b/drivers/char/agp/backend.c
@@ -189,9 +189,11 @@ static int agp_backend_initialize(struct agp_bridge_data *bridge)
 
 err_out:
 	if (bridge->driver->needs_scratch_page) {
-		bridge->driver->agp_destroy_page(
-				gart_to_virt(bridge->scratch_page_real));
+		bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
+						 AGP_PAGE_DESTROY_UNMAP);
 		flush_agp_mappings();
+		bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
+						 AGP_PAGE_DESTROY_FREE);
 	}
 	if (got_gatt)
 		bridge->driver->free_gatt_table(bridge);
@@ -215,9 +217,11 @@ static void agp_backend_cleanup(struct agp_bridge_data *bridge)
 
 	if (bridge->driver->agp_destroy_page &&
 	    bridge->driver->needs_scratch_page) {
-		bridge->driver->agp_destroy_page(
-				gart_to_virt(bridge->scratch_page_real));
+		bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
+						 AGP_PAGE_DESTROY_UNMAP);
 		flush_agp_mappings();
+		bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
+						 AGP_PAGE_DESTROY_FREE);
 	}
 }
 
diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index 3db4f40..1cdbed9 100644
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -195,9 +195,12 @@ void agp_free_memory(struct agp_memory *curr)
 	}
 	if (curr->page_count != 0) {
 		for (i = 0; i < curr->page_count; i++) {
-			curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]));
+			curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]), AGP_PAGE_DESTROY_UNMAP);
 		}
 		flush_agp_mappings();
+		for (i = 0; i < curr->page_count; i++) {
+			curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]), AGP_PAGE_DESTROY_FREE);
+		}
 	}
 	agp_free_key(curr->key);
 	agp_free_page_array(curr);
@@ -1176,7 +1179,7 @@ void *agp_generic_alloc_page(struct agp_bridge_data *bridge)
 EXPORT_SYMBOL(agp_generic_alloc_page);
 
 
-void agp_generic_destroy_page(void *addr)
+void agp_generic_destroy_page(void *addr, int flags)
 {
 	struct page *page;
 
@@ -1184,10 +1187,15 @@ void agp_generic_destroy_page(void *addr)
 		return;
 
 	page = virt_to_page(addr);
-	unmap_page_from_agp(page);
-	put_page(page);
-	free_page((unsigned long)addr);
-	atomic_dec(&agp_bridge->current_memory_agp);
+	if (flags & AGP_PAGE_DESTROY_UNMAP) {
+		unmap_page_from_agp(page);
+	} 
+
+	if (flags & AGP_PAGE_DESTROY_FREE) {
+		put_page(page);
+		free_page((unsigned long)addr);
+		atomic_dec(&agp_bridge->current_memory_agp);
+	}
 }
 EXPORT_SYMBOL(agp_generic_destroy_page);
 
diff --git a/drivers/char/agp/i460-agp.c b/drivers/char/agp/i460-agp.c
index 75d2aca..70117df 100644
--- a/drivers/char/agp/i460-agp.c
+++ b/drivers/char/agp/i460-agp.c
@@ -536,10 +536,10 @@ static void *i460_alloc_page (struct agp_bridge_data *bridge)
 	return page;
 }
 
-static void i460_destroy_page (void *page)
+static void i460_destroy_page (void *page, int flags)
 {
 	if (I460_IO_PAGE_SHIFT <= PAGE_SHIFT) {
-		agp_generic_destroy_page(page);
+		agp_generic_destroy_page(page, flags);
 		global_flush_tlb();
 	}
 }
diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
index a5d0e95..c0c10ea 100644
--- a/drivers/char/agp/intel-agp.c
+++ b/drivers/char/agp/intel-agp.c
@@ -400,9 +400,11 @@ static void intel_i810_free_by_type(struct agp_memory *curr)
 		if (curr->page_count == 4)
 			i8xx_destroy_pages(gart_to_virt(curr->memory[0]));
 		else {
-			agp_bridge->driver->agp_destroy_page(
-				 gart_to_virt(curr->memory[0]));
+			agp_bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[0]),
+							     AGP_PAGE_DESTROY_UNMAP);
 			global_flush_tlb();
+			agp_bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[0]),
+							     AGP_PAGE_DESTROY_FREE);
 		}
 		agp_free_page_array(curr);
 	}
-- 
1.5.2.4