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    Subject[PATCH 6/6] UML - Fix LVM crash
    From: Jason Lunz <lunz@falooley.org>

    Permit lvm to create logical volumes without crashing UML.

    When device-mapper's 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) is called.

    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.

    This ensures init_emergency_isa_pool() doesn't crash uml in this
    situation by setting max_low_pfn == max_pfn in mem_init().

    Signed-off-by: Jason Lunz <lunz@falooley.org>
    Signed-off-by: Jeff Dike <jdike@linux.intel.com>
    ---
    arch/um/kernel/mem.c | 3 +--
    1 file changed, 1 insertion(+), 2 deletions(-)

    Index: linux-2.6.21-mm/arch/um/kernel/mem.c
    ===================================================================
    --- linux-2.6.21-mm.orig/arch/um/kernel/mem.c 2007-03-27 12:25:10.000000000 -0400
    +++ linux-2.6.21-mm/arch/um/kernel/mem.c 2007-03-27 12:58:36.000000000 -0400
    @@ -64,8 +64,6 @@ static void setup_highmem(unsigned long

    void mem_init(void)
    {
    - max_low_pfn = (high_physmem - uml_physmem) >> PAGE_SHIFT;
    -
    /* clear the zero-page */
    memset((void *) empty_zero_page, 0, PAGE_SIZE);

    @@ -80,6 +78,7 @@ void mem_init(void)

    /* this will put all low memory onto the freelists */
    totalram_pages = free_all_bootmem();
    + max_low_pfn = totalram_pages;
    #ifdef CONFIG_HIGHMEM
    totalhigh_pages = highmem >> PAGE_SHIFT;
    totalram_pages += totalhigh_pages;
    -
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