From: Kan Liang <kan.liang@xxxxxxxxx>
Subject: 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 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@xxxxxxxxx
Fixes: 2947ba054a4d ("x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation")
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Ying Huang <ying.huang@xxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/pagemap.h | 2 --
1 file changed, 2 deletions(-)
diff -puN include/linux/pagemap.h~mm-allow-page_cache_get_speculative-in-interrupt-context include/linux/pagemap.h
--- a/include/linux/pagemap.h~mm-allow-page_cache_get_speculative-in-interrupt-context
+++ a/include/linux/pagemap.h
@@ -163,8 +163,6 @@ void release_pages(struct page **pages,
*/
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());
_
--
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