[PATCH mmotm] memcg: unmap KM_USER0 at shmem_map_and_free_swp if do_swap_account

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

memswap controller uses KM_USER0 at swap_cgroup_record and lookup_swap_cgroup.

But delete_from_swap_cache, which eventually calls swap_cgroup_record, can be
called with KM_USER0 mapped in case of shmem.

So it should be unmapped before calling it.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
After this patch, I think memswap controller of x86_32 will be
on the same level with that of x86_64.

 mm/shmem.c |   23 +++++++++++++++++++++++
 1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index bee8612..7aebc1b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -171,6 +171,28 @@ static inline void shmem_unacct_size(unsigned long flags, loff_t size)
 		vm_unacct_memory(VM_ACCT(size));
 }
 
+#if defined(CONFIG_CGROUP_MEM_RES_CTLR_SWAP) && defined(CONFIG_HIGHMEM)
+/*
+ * memswap controller uses KM_USER0, so dir should be unmapped
+ * before calling delete_from_swap_cache.
+ */
+static inline void swap_cgroup_map_prepare(struct page ***dir)
+{
+	if (!do_swap_account)
+		return;
+
+	if (*dir) {
+		shmem_dir_unmap(*dir);
+		*dir = NULL;
+	}
+}
+#else
+static inline void swap_cgroup_map_prepare(struct page ***dir)
+{
+	return;
+}
+#endif
+
 /*
  * ... whereas tmpfs objects are accounted incrementally as
  * pages are allocated, in order to allow huge sparse files.
@@ -479,6 +501,7 @@ static int shmem_map_and_free_swp(struct page *subdir, int offset,
 		int size = limit - offset;
 		if (size > LATENCY_LIMIT)
 			size = LATENCY_LIMIT;
+		swap_cgroup_map_prepare(dir);
 		freed += shmem_free_swp(ptr+offset, ptr+offset+size,
 							punch_lock);
 		if (need_resched()) {

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