block: initialize the bounce pool if high memory may be added later

init_emergency_pool() does not create the page pool for bouncing block requests if the current count of high pages is zero. If high memory may be added later (either via memory hotplug or a balloon driver in a virtualized system) then a oops occurs if a request with a high page need bouncing because the pool does not exist.

So, always create the pool if memory hotplug is enabled and change the test so it's valid even if all high pages are currently in the balloon (the balloon drivers adjust totalhigh_pages but not max_pfn).

Signed-off-by David Vrabel <[email protected]>

---
 mm/bounce.c |    9 ++++-----
 1 files changed, 4 insertions(+), 5 deletions(-)

mm/bounce.c +4 -5

index 1481de6..434fb4f 100644
@@ -14,6 +14,7 @@
 #include <linux/init.h>
 #include <linux/hash.h>
 #include <linux/highmem.h>
+#include <linux/bootmem.h>
 #include <asm/tlbflush.h>
 
 #include <trace/events/block.h>

@@ -26,12 +27,10 @@ static mempool_t *page_pool, *isa_page_pool;
 #ifdef CONFIG_HIGHMEM
 static __init int init_emergency_pool(void)
 {
-	struct sysinfo i;
-	si_meminfo(&i);
-	si_swapinfo(&i);
-
-	if (!i.totalhigh)
+#ifndef CONFIG_MEMORY_HOTPLUG
+	if (max_pfn <= max_low_pfn)
 		return 0;
+#endif
 
 	page_pool = mempool_create_page_pool(POOL_SIZE, 0);
 	BUG_ON(!page_pool);

Quoted 6 lines · David Vrabel

init_emergency_pool() does not create the page pool for bouncing block requests if the current count of high pages is zero. If high memory may be added later (either via memory hotplug or a balloon driver in a virtualized system) then a oops occurs if a request with a high page need bouncing because the pool does not exist.

Quoted 3 lines

So, always create the pool if memory hotplug is enabled and change the test so it's valid even if all high pages are currently in the balloon (the balloon drivers adjust totalhigh_pages but not max_pfn).

Jens, you don't seem to have picked up this patch yet. Should it have gone via Andrew Morton instead?