[uml-devel] [UML] fix crash in block layer

[Jason Lunz <lunz@falooley.org>]

When the device-mapper DM_DEV_CREATE_CMD ioctl is called to create a new
device, dev_create()->dm_create()->alloc_dev()->
blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY) happens.

blk_queue_bounce_limit(BLK_BOUNCE_ANY) calls init_emergency_isa_pool()
if blk_max_pfn < blk_max_low_pfn. This is the case on UML, but
init_emergency_isa_pool() hits BUG_ON(!isa_page_pool) because there
doesn't seem to be a dma zone on UML for mempool_create() to allocate from.

Most architectures seem to have max_low_pfn == max_pfn, but UML doesn't
because of the uml_reserved chunk it keeps for itself. From what I can
see, max_pfn and max_low_pfn don't get much use after the
bootmem-allocator stops being used anyway, except that they initialize
the block layer's blk_max_low_pfn/blk_max_pfn.

With this applied I can use lvm to create logical volumes without
crashing UML.

Signed-off-by: Jason Lunz <lunz@falooley.org>

---
 arch/um/kernel/mem.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Index: linux-2.6.20-rc5-uml/arch/um/kernel/mem.c
===================================================================
--- linux-2.6.20-rc5-uml.orig/arch/um/kernel/mem.c
+++ linux-2.6.20-rc5-uml/arch/um/kernel/mem.c
@@ -63,7 +63,7 @@
 
 void mem_init(void)
 {
-	max_low_pfn = (high_physmem - uml_physmem) >> PAGE_SHIFT;
+	max_pfn = max_low_pfn = (high_physmem - uml_physmem) >> PAGE_SHIFT;
 
         /* clear the zero-page */
         memset((void *) empty_zero_page, 0, PAGE_SIZE);
@@ -84,7 +84,6 @@
 	totalram_pages += totalhigh_pages;
 #endif
 	num_physpages = totalram_pages;
-	max_pfn = totalram_pages;
 	printk(KERN_INFO "Memory: %luk available\n", 
 	       (unsigned long) nr_free_pages() << (PAGE_SHIFT-10));
 	kmalloc_ok = 1;

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