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Subject[240/289] ARM: 6464/2: fix spinlock recursion in adjust_pte()
2.6.36-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Mika Westerberg <mika.westerberg@iki.fi>

commit 4e54d93d3c9846ba1c2644ad06463dafa690d1b7 upstream.

When running following code in a machine which has VIVT caches and
USE_SPLIT_PTLOCKS is not defined:

fd = open("/etc/passwd", O_RDONLY);
addr = mmap(NULL, 4096, PROT_READ, MAP_SHARED, fd, 0);
addr2 = mmap(NULL, 4096, PROT_READ, MAP_SHARED, fd, 0);

v = *((int *)addr);

we will hang in spinlock recursion in the page fault handler:

BUG: spinlock recursion on CPU#0, mmap_test/717
lock: c5e295d8, .magic: dead4ead, .owner: mmap_test/717,
.owner_cpu: 0
[<c0026604>] (unwind_backtrace+0x0/0xec)
[<c014ee48>] (do_raw_spin_lock+0x40/0x140)
[<c0027f68>] (update_mmu_cache+0x208/0x250)
[<c0079db4>] (__do_fault+0x320/0x3ec)
[<c007af7c>] (handle_mm_fault+0x2f0/0x6d8)
[<c0027834>] (do_page_fault+0xdc/0x1cc)
[<c00202d0>] (do_DataAbort+0x34/0x94)

This comes from the fact that when USE_SPLIT_PTLOCKS is not defined,
the only lock protecting the page tables is mm->page_table_lock
which is already locked before update_mmu_cache() is called.

Signed-off-by: Mika Westerberg <mika.westerberg@iki.fi>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/arm/mm/fault-armv.c | 28 ++++++++++++++++++++++++++--
1 file changed, 26 insertions(+), 2 deletions(-)
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -65,6 +65,30 @@ static int do_adjust_pte(struct vm_area_
return ret;
}

+#if USE_SPLIT_PTLOCKS
+/*
+ * If we are using split PTE locks, then we need to take the page
+ * lock here. Otherwise we are using shared mm->page_table_lock
+ * which is already locked, thus cannot take it.
+ */
+static inline void do_pte_lock(spinlock_t *ptl)
+{
+ /*
+ * Use nested version here to indicate that we are already
+ * holding one similar spinlock.
+ */
+ spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+}
+
+static inline void do_pte_unlock(spinlock_t *ptl)
+{
+ spin_unlock(ptl);
+}
+#else /* !USE_SPLIT_PTLOCKS */
+static inline void do_pte_lock(spinlock_t *ptl) {}
+static inline void do_pte_unlock(spinlock_t *ptl) {}
+#endif /* USE_SPLIT_PTLOCKS */
+
static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
unsigned long pfn)
{
@@ -89,11 +113,11 @@ static int adjust_pte(struct vm_area_str
*/
ptl = pte_lockptr(vma->vm_mm, pmd);
pte = pte_offset_map_nested(pmd, address);
- spin_lock(ptl);
+ do_pte_lock(ptl);

ret = do_adjust_pte(vma, address, pfn, pte);

- spin_unlock(ptl);
+ do_pte_unlock(ptl);
pte_unmap_nested(pte);

return ret;



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