From: Mika Westerberg <mika.westerberg@iki.fi>
Date: Thu, 28 Oct 2010 10:45:22 +0000 (+0100)
Subject: ARM: 6464/2: fix spinlock recursion in adjust_pte()
X-Git-Tag: v2.6.37-rc1~23^2~10
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4e54d93d3c9846ba1c2644ad06463dafa690d1b7;p=pandora-kernel.git

ARM: 6464/2: fix spinlock recursion in adjust_pte()

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>
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