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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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