[PATCH] rmap 22 flush_dcache_mmap_lock

Hugh Dickins
2004-05-04T22:22:41Z

arm and parisc __flush_dcache_page have been scanning the i_mmap(_shared)
list without locking or disabling preemption. That may be even more
unsafe now it's a prio tree instead of a list.

It looks like we cannot use i_shared_lock for this protection: most uses
of flush_dcache_page are okay, and only one would need lock ordering
fixed (get_user_pages holds page_table_lock across flush_dcache_page);
but there's a few (e.g. in net and ntfs) which look as if they're using
it in I/O completion - and it would be restrictive to disallow it there.

So, on arm and parisc only, define flush_dcache_mmap_lock(mapping) as
spin_lock_irq(&(mapping)->tree_lock); on i386 (and other arches left
to the next patch) define it away to nothing; and use where needed.

While updating locking hierarchy in filemap.c, remove two layers of the
fossil record from add_to_page_cache comment: no longer used for swap.

I believe all the #includes will work out, but have only built i386.
I can see several things about this patch which might cause revulsion:
the name flush_dcache_mmap_lock? the reuse of the page radix_tree's
tree_lock for this different purpose? spin_lock_irqsave instead?
can't we somehow get i_shared_lock to handle the problem?

arch/arm/mm/fault-armv.c | 5 +++++
arch/parisc/kernel/cache.c | 2 ++
include/asm-arm/cacheflush.h | 5 +++++
include/asm-i386/cacheflush.h | 2 ++
include/asm-parisc/cacheflush.h | 5 +++++
kernel/fork.c | 2 ++
mm/filemap.c | 10 +++-------
mm/fremap.c | 2 ++
mm/mmap.c | 10 +++++++++-
9 files changed, 35 insertions(+), 8 deletions(-)

--- rmap21/arch/arm/mm/fault-armv.c 2004-05-04 21:21:28.883451832 +0100
+++ rmap22/arch/arm/mm/fault-armv.c 2004-05-04 21:21:50.954096584 +0100
@@ -94,6 +94,8 @@ void __flush_dcache_page(struct page *pa
* and invalidate any user data.
*/
pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+
+ flush_dcache_mmap_lock(mapping);
while ((mpnt = vma_prio_tree_next(mpnt, &mapping->i_mmap,
&iter, pgoff, pgoff)) != NULL) {
/*
@@ -106,6 +108,7 @@ void __flush_dcache_page(struct page *pa
offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
flush_cache_page(mpnt, mpnt->vm_start + offset);
}
+ flush_dcache_mmap_unlock(mapping);
}

static void
@@ -129,6 +132,7 @@ make_coherent(struct vm_area_struct *vma
* space, then we need to handle them specially to maintain
* cache coherency.
*/
+ flush_dcache_mmap_lock(mapping);
while ((mpnt = vma_prio_tree_next(mpnt, &mapping->i_mmap,
&iter, pgoff, pgoff)) != NULL) {
/*
@@ -143,6 +147,7 @@ make_coherent(struct vm_area_struct *vma
offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
aliases += adjust_pte(mpnt, mpnt->vm_start + offset);
}
+ flush_dcache_mmap_unlock(mapping);
if (aliases)
adjust_pte(vma, addr);
else
--- rmap21/arch/parisc/kernel/cache.c 2004-05-04 21:21:28.883451832 +0100
+++ rmap22/arch/parisc/kernel/cache.c 2004-05-04 21:21:50.955096432 +0100
@@ -244,6 +244,7 @@ void __flush_dcache_page(struct page *pa

pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

+ flush_dcache_mmap_lock(mapping);
while ((mpnt = vma_prio_tree_next(mpnt, &mapping->i_mmap,
&iter, pgoff, pgoff)) != NULL) {
/*
@@ -262,6 +263,7 @@ void __flush_dcache_page(struct page *pa
*/
break;
}
+ flush_dcache_mmap_unlock(mapping);
}
EXPORT_SYMBOL(__flush_dcache_page);

--- rmap21/include/asm-arm/cacheflush.h 2004-04-28 07:07:11.000000000 +0100
+++ rmap22/include/asm-arm/cacheflush.h 2004-05-04 21:21:50.956096280 +0100
@@ -303,6 +303,11 @@ static inline void flush_dcache_page(str
__flush_dcache_page(page);
}

+#define flush_dcache_mmap_lock(mapping) \
+ spin_lock_irq(&(mapping)->tree_lock)
+#define flush_dcache_mmap_unlock(mapping) \
+ spin_unlock_irq(&(mapping)->tree_lock)
+
#define flush_icache_user_range(vma,page,addr,len) \
flush_dcache_page(page)

--- rmap21/include/asm-i386/cacheflush.h 2003-10-08 20:24:56.000000000 +0100
+++ rmap22/include/asm-i386/cacheflush.h 2004-05-04 21:21:50.956096280 +0100
@@ -10,6 +10,8 @@
#define flush_cache_range(vma, start, end) do { } while (0)
#define flush_cache_page(vma, vmaddr) do { } while (0)
#define flush_dcache_page(page) do { } while (0)
+#define flush_dcache_mmap_lock(mapping) do { } while (0)
+#define flush_dcache_mmap_unlock(mapping) do { } while (0)
#define flush_icache_range(start, end) do { } while (0)
#define flush_icache_page(vma,pg) do { } while (0)
#define flush_icache_user_range(vma,pg,adr,len) do { } while (0)
--- rmap21/include/asm-parisc/cacheflush.h 2004-04-28 07:07:13.000000000 +0100
+++ rmap22/include/asm-parisc/cacheflush.h 2004-05-04 21:21:50.957096128 +0100
@@ -78,6 +78,11 @@ static inline void flush_dcache_page(str
}
}

+#define flush_dcache_mmap_lock(mapping) \
+ spin_lock_irq(&(mapping)->tree_lock)
+#define flush_dcache_mmap_unlock(mapping) \
+ spin_unlock_irq(&(mapping)->tree_lock)
+
#define flush_icache_page(vma,page) do { flush_kernel_dcache_page(page_address(page)); flush_kernel_icache_page(page_address(page)); } while (0)

#define flush_icache_range(s,e) do { flush_kernel_dcache_range_asm(s,e); flush_kernel_icache_range_asm(s,e); } while (0)
--- rmap21/kernel/fork.c 2004-04-30 11:58:46.000000000 +0100
+++ rmap22/kernel/fork.c 2004-05-04 21:21:50.958095976 +0100
@@ -331,7 +331,9 @@ static inline int dup_mmap(struct mm_str

/* insert tmp into the share list, just after mpnt */
spin_lock(&file->f_mapping->i_shared_lock);
+ flush_dcache_mmap_lock(mapping);
vma_prio_tree_add(tmp, mpnt);
+ flush_dcache_mmap_unlock(mapping);
spin_unlock(&file->f_mapping->i_shared_lock);
}

--- rmap21/mm/filemap.c 2004-04-30 11:58:47.000000000 +0100
+++ rmap22/mm/filemap.c 2004-05-04 21:21:50.960095672 +0100
@@ -65,7 +65,9 @@
* ->i_shared_lock (truncate->unmap_mapping_range)
*
* ->mmap_sem
- * ->i_shared_lock (various places)
+ * ->i_shared_lock
+ * ->page_table_lock (various places, mainly in mmap.c)
+ * ->mapping->tree_lock (arch-dependent flush_dcache_mmap_lock)
*
* ->mmap_sem
* ->lock_page (access_process_vm)
@@ -240,12 +242,6 @@ int filemap_write_and_wait(struct addres
}

/*
- * This adds a page to the page cache, starting out as locked, unreferenced,
- * not uptodate and with no errors.
- *
- * This function is used for two things: adding newly allocated pagecache
- * pages and for moving existing anon pages into swapcache.
- *
* This function is used to add newly allocated pagecache pages:
* the page is new, so we can just run SetPageLocked() against it.
* The other page state flags were set by rmqueue().
--- rmap21/mm/fremap.c 2004-05-04 21:21:28.890450768 +0100
+++ rmap22/mm/fremap.c 2004-05-04 21:21:50.961095520 +0100
@@ -202,11 +202,13 @@ asmlinkage long sys_remap_file_pages(uns
!(vma->vm_flags & VM_NONLINEAR)) {
mapping = vma->vm_file->f_mapping;
spin_lock(&mapping->i_shared_lock);
+ flush_dcache_mmap_lock(mapping);
vma->vm_flags |= VM_NONLINEAR;
vma_prio_tree_remove(vma, &mapping->i_mmap);
vma_prio_tree_init(vma);
list_add_tail(&vma->shared.vm_set.list,
&mapping->i_mmap_nonlinear);
+ flush_dcache_mmap_unlock(mapping);
spin_unlock(&mapping->i_shared_lock);
}

--- rmap21/mm/mmap.c 2004-05-04 21:21:28.894450160 +0100
+++ rmap22/mm/mmap.c 2004-05-04 21:21:50.963095216 +0100
@@ -23,6 +23,7 @@
#include <linux/mount.h>

#include <asm/uaccess.h>
+#include <asm/cacheflush.h>
#include <asm/tlb.h>

/*
@@ -72,10 +73,12 @@ static inline void __remove_shared_vm_st
if (vma->vm_flags & VM_SHARED)
mapping->i_mmap_writable--;

+ flush_dcache_mmap_lock(mapping);
if (unlikely(vma->vm_flags & VM_NONLINEAR))
list_del_init(&vma->shared.vm_set.list);
else
vma_prio_tree_remove(vma, &mapping->i_mmap);
+ flush_dcache_mmap_unlock(mapping);
}

/*
@@ -264,11 +267,13 @@ static inline void __vma_link_file(struc
if (vma->vm_flags & VM_SHARED)
mapping->i_mmap_writable++;

+ flush_dcache_mmap_lock(mapping);
if (unlikely(vma->vm_flags & VM_NONLINEAR))
list_add_tail(&vma->shared.vm_set.list,
&mapping->i_mmap_nonlinear);
else
vma_prio_tree_insert(vma, &mapping->i_mmap);
+ flush_dcache_mmap_unlock(mapping);
}
}

@@ -348,14 +353,17 @@ void vma_adjust(struct vm_area_struct *v
}
spin_lock(&mm->page_table_lock);

- if (root)
+ if (root) {
+ flush_dcache_mmap_lock(mapping);
vma_prio_tree_remove(vma, root);
+ }
vma->vm_start = start;
vma->vm_end = end;
vma->vm_pgoff = pgoff;
if (root) {
vma_prio_tree_init(vma);
vma_prio_tree_insert(vma, root);
+ flush_dcache_mmap_unlock(mapping);
}

if (next) {