[PATCH 4.9 074/241] mm: Fix false-positive VM_BUG_ON() in page_cache_{get,add}_speculative()

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Kirill A. Shutemov" <redacted>


[ 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 <redacted>
Signed-off-by: Kirill A. Shutemov <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aneesh Kumar K.V <redacted>
Cc: Kirill A. Shutemov <redacted>
Cc: LKP <redacted>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <redacted>
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 <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/pagemap.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h

@@ -148,7 +148,7 @@ static inline int page_cache_get_specula
 
 #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_specula
 
 #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);