[Xen-devel] Re: kernel BUG at arch/x86/xen/mmu.c:1872

[Teck Choon Giam <giamteckchoon@xxxxxxxxx>]

From: Giam Teck Choon <giamteckchoon@xxxxxxxxx>

vmalloc: eagerly clear ptes on vunmap

Backport from commit 64141da587241301ce8638cc945f8b67853156ec to 2.6.32.36

URL: 
http://git.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=commit;h=64141da587241301ce8638cc945f8b67853156ec

Without this patch, kernel BUG at arch/x86/xen/mmu.c:1860 or kernel BUG at
arch/x86/xen/mmu.c:1872 is easily triggered when CONFIG_DEBUG_PAGEALLOC is
unset especially doing LVM snapshots.

Signed-off-by: Giam Teck Choon <giamteckchoon@xxxxxxxxx>
---
 arch/x86/xen/mmu.c      |    2 --
 include/linux/vmalloc.h |    2 --
 mm/vmalloc.c            |   28 +++++++++++++++++-----------
 3 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index fa36ab8..204e3ba 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -2430,8 +2430,6 @@ void __init xen_init_mmu_ops(void)
        x86_init.paging.pagetable_setup_start = xen_pagetable_setup_start;
        x86_init.paging.pagetable_setup_done = xen_pagetable_setup_done;
        pv_mmu_ops = xen_mmu_ops;
-
-       vmap_lazy_unmap = false;
 }

 /* Protected by xen_reservation_lock. */
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 1a2ba21..3c123c3 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -7,8 +7,6 @@

 struct vm_area_struct;         /* vma defining user mapping in mm_types.h */

-extern bool vmap_lazy_unmap;
-
 /* bits in flags of vmalloc's vm_struct below */
 #define VM_IOREMAP     0x00000001      /* ioremap() and friends */
 #define VM_ALLOC       0x00000002      /* vmalloc() */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 4f701c2..80cbd7b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -31,8 +31,6 @@
 #include <asm/tlbflush.h>
 #include <asm/shmparam.h>

-bool vmap_lazy_unmap __read_mostly = true;
-
 /*** Page table manipulation functions ***/

 static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end)
@@ -503,9 +501,6 @@ static unsigned long lazy_max_pages(void)
 {
        unsigned int log;

-       if (!vmap_lazy_unmap)
-               return 0;
-
        log = fls(num_online_cpus());

        return log * (32UL * 1024 * 1024 / PAGE_SIZE);
@@ -566,7 +561,6 @@ static void __purge_vmap_area_lazy(unsigned long
*start, unsigned long *end,
                        if (va->va_end > *end)
                                *end = va->va_end;
                        nr += (va->va_end - va->va_start) >> PAGE_SHIFT;
-                       unmap_vmap_area(va);
                        list_add_tail(&va->purge_list, &valist);
                        va->flags |= VM_LAZY_FREEING;
                        va->flags &= ~VM_LAZY_FREE;
@@ -612,10 +606,11 @@ static void purge_vmap_area_lazy(void)
 }

 /*
- * Free and unmap a vmap area, caller ensuring flush_cache_vunmap had been
- * called for the correct range previously.
+ * Free a vmap area, caller ensuring that the area has been unmapped
+ * and flush_cache_vunmap had been called for the correct range
+ * previously.
  */
-static void free_unmap_vmap_area_noflush(struct vmap_area *va)
+static void free_vmap_area_noflush(struct vmap_area *va)
 {
        va->flags |= VM_LAZY_FREE;
        atomic_add((va->va_end - va->va_start) >> PAGE_SHIFT, &vmap_lazy_nr);
@@ -624,6 +619,16 @@ static void free_unmap_vmap_area_noflush(struct
vmap_area *va)
 }

 /*
+ * Free and unmap a vmap area, caller ensuring flush_cache_vunmap had been
+ * called for the correct range previously.
+ */
+static void free_unmap_vmap_area_noflush(struct vmap_area *va)
+{
+       unmap_vmap_area(va);
+       free_vmap_area_noflush(va);
+}
+
+/*
  * Free and unmap a vmap area
  */
 static void free_unmap_vmap_area(struct vmap_area *va)
@@ -799,7 +804,7 @@ static void free_vmap_block(struct vmap_block *vb)
        spin_unlock(&vmap_block_tree_lock);
        BUG_ON(tmp != vb);

-       free_unmap_vmap_area_noflush(vb->va);
+       free_vmap_area_noflush(vb->va);
        call_rcu(&vb->rcu_head, rcu_free_vb);
 }

@@ -936,6 +941,8 @@ static void vb_free(const void *addr, unsigned long size)
        rcu_read_unlock();
        BUG_ON(!vb);

+       vunmap_page_range((unsigned long)addr, (unsigned long)addr + size);
+
        spin_lock(&vb->lock);
        BUG_ON(bitmap_allocate_region(vb->dirty_map, offset >> PAGE_SHIFT, 
order));

@@ -988,7 +995,6 @@ void vm_unmap_aliases(void)

                                s = vb->va->va_start + (i << PAGE_SHIFT);
                                e = vb->va->va_start + (j << PAGE_SHIFT);
-                               vunmap_page_range(s, e);
                                flush = 1;

                                if (s < start)

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