mm: Fix false-positive VM_BUG_ON() in page_cache_{get,add}_speculative()

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>

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);