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    Subject[PATCH AUTOSEL for 4.9 077/219] mm: Fix false-positive VM_BUG_ON() in page_cache_{get,add}_speculative()
    Date
    From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

    [ Upstream commit 591a3d7c09fa08baff48ad86c2347dbd28a52753 ]

    0day testing by Fengguang Wu triggered this crash while running Trinity:

    kernel BUG at include/linux/pagemap.h:151!
    ...
    CPU: 0 PID: 458 Comm: trinity-c0 Not tainted 4.11.0-rc2-00251-g2947ba0 #1
    ...
    Call Trace:
    __get_user_pages_fast()
    get_user_pages_fast()
    get_futex_key()
    futex_requeue()
    do_futex()
    SyS_futex()
    do_syscall_64()
    entry_SYSCALL64_slow_path()

    It' VM_BUG_ON() due to false-negative in_atomic(). We call
    page_cache_get_speculative() with disabled local interrupts.
    It should be atomic enough.

    So let's check for disabled interrupts in the VM_BUG_ON() condition
    too, to resolve this.

    ( This got triggered by the conversion of the x86 GUP code to the
    generic GUP code. )

    Reported-by: Fengguang Wu <fengguang.wu@intel.com>
    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Cc: Kirill A. Shutemov <kirill@shutemov.name>
    Cc: LKP <lkp@01.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-mm@kvack.org
    Link: http://lkml.kernel.org/r/20170324114709.pcytvyb3d6ajux33@black.fi.intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    include/linux/pagemap.h | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
    index 7dbe9148b2f8..35f4c4d9c405 100644
    --- a/include/linux/pagemap.h
    +++ b/include/linux/pagemap.h
    @@ -148,7 +148,7 @@ static inline int page_cache_get_speculative(struct page *page)

    #ifdef CONFIG_TINY_RCU
    # ifdef CONFIG_PREEMPT_COUNT
    - VM_BUG_ON(!in_atomic());
    + VM_BUG_ON(!in_atomic() && !irqs_disabled());
    # endif
    /*
    * Preempt must be disabled here - we rely on rcu_read_lock doing
    @@ -186,7 +186,7 @@ static inline int page_cache_add_speculative(struct page *page, int count)

    #if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
    # ifdef CONFIG_PREEMPT_COUNT
    - VM_BUG_ON(!in_atomic());
    + VM_BUG_ON(!in_atomic() && !irqs_disabled());
    # endif
    VM_BUG_ON_PAGE(page_count(page) == 0, page);
    page_ref_add(page, count);
    --
    2.14.1
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