mm: allow page_cache_get_speculative in interrupt context
authorKan Liang <kan.liang@intel.com>
Wed, 2 Aug 2017 20:32:27 +0000 (13:32 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 3 Aug 2017 00:16:13 +0000 (17:16 -0700)
commit1ee1c3f5b5cff959e0ac95a125bd15eaf88cc638
tree18e5ee0fe0ccf7960c9e09eb51d968098fd420f1
parent5a18b64e3f02125be1c0ef777501ae38aafe2a24
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 <kan.liang@intel.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Ying Huang <ying.huang@intel.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
include/linux/pagemap.h