[PATCH] mm: non-atomically mark page accessed during page cache allocation where possible -fix

[Mel Gorman]

Prabhakar Lad reported the following problem

  I see following issue on DA850 evm,
  git bisect points me to
  commit id: 975c3a671f11279441006a29a19f55ccc15fb320
  ( mm: non-atomically mark page accessed during page cache allocation
  where possible)

  Unable to handle kernel paging request at virtual address 30e03501
  pgd = c68cc000
  [30e03501] *pgd=00000000
  Internal error: Oops: 1 [#1] PREEMPT ARM
  Modules linked in:
  CPU: 0 PID: 1015 Comm: network.sh Not tainted 3.15.0-rc5-00323-g975c3a6 #9
  task: c70c4e00 ti: c73d0000 task.ti: c73d0000
  PC is at init_page_accessed+0xc/0x24
  LR is at shmem_write_begin+0x54/0x60
  pc : [<c0088aa0>]    lr : [<c00923e8>]    psr: 20000013
  sp : c73d1d90  ip : c73d1da0  fp : c73d1d9c
  r10: c73d1dec  r9 : 00000000  r8 : 00000000
  r7 : c73d1e6c  r6 : c694d7bc  r5 : ffffffe4  r4 : c73d1dec
  r3 : c73d0000  r2 : 00000001  r1 : 00000000  r0 : 30e03501
  Flags: nzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
  Control: 0005317f  Table: c68cc000  DAC: 00000015
  Process network.sh (pid: 1015, stack limit = 0xc73d01c0)

pagep is set but not pointing to anywhere valid as it's an uninitialised
stack variable. This patch is a fix to
mm-non-atomically-mark-page-accessed-during-page-cache-allocation-where-possible.patch

Reported-by: Prabhakar Lad <prabhakar.csengg@xxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 mm/filemap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 2a7b9d1..0691481 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2459,7 +2459,7 @@ ssize_t generic_perform_write(struct file *file,
 		flags |= AOP_FLAG_UNINTERRUPTIBLE;
 
 	do {
-		struct page *page;
+		struct page *page = NULL;
 		unsigned long offset;	/* Offset into pagecache page */
 		unsigned long bytes;	/* Bytes to write to page */
 		size_t copied;		/* Bytes copied from user */
--
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