From 1ee1c3f5b5cff959e0ac95a125bd15eaf88cc638 Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Wed, 2 Aug 2017 13:32:27 -0700 Subject: [PATCH] mm: allow page_cache_get_speculative in interrupt context Kernel panic when calling the IRQ-safe __get_user_pages_fast in NMI handler. The bug was introduced by commit 2947ba054a4d ("x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation"). The original x86 __get_user_page_fast used plain get_page() or page_ref_add(). However, the generic __get_user_page_fast uses page_cache_get_speculative(), which has VM_BUG_ON(in_interrupt()). There is no reason to prevent page_cache_get_speculative from using in interrupt context. According to the author, putting a BUG_ON there is just because the code is not verifying correctness of interrupt races. I did some tests in interrupt context. There is no issue found. Removing VM_BUG_ON(in_interrupt()) for page_cache_get_speculative(). Link: http://lkml.kernel.org/r/1501609146-59730-1-git-send-email-kan.liang@intel.com Fixes: 2947ba054a4d ("x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation") Signed-off-by: Kan Liang Cc: Jens Axboe Cc: Al Viro Cc: Kirill A. Shutemov Cc: Ying Huang Cc: Nicholas Piggin Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/pagemap.h | 2 -- 1 file changed, 2 deletions(-) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index baa9344dcd10..79b36f57c3ba 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -163,8 +163,6 @@ void release_pages(struct page **pages, int nr, bool cold); */ static inline int page_cache_get_speculative(struct page *page) { - VM_BUG_ON(in_interrupt()); - #ifdef CONFIG_TINY_RCU # ifdef CONFIG_PREEMPT_COUNT VM_BUG_ON(!in_atomic() && !irqs_disabled());