mm: frontswap: split frontswap_shrink further to simplify locking

Split frontswap_shrink to simplify the locking in the original code.

Also, assert that the function that was split still runs under the
swap spinlock.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 21 insertions, 15 deletions

diff --git a/mm/frontswap.c b/mm/frontswap.c
index faa43b7eea6f..e6353d9151ee 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -265,6 +265,24 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
         return ret;
 }
 
+static int __frontswap_shrink(unsigned long target_pages,
+                                unsigned long *pages_to_unuse,
+                                int *type)
+{
+        unsigned long total_pages = 0, total_pages_to_unuse;
+
+        assert_spin_locked(&swap_lock);
+
+        total_pages = __frontswap_curr_pages();
+        if (total_pages <= target_pages) {
+                /* Nothing to do */
+                *pages_to_unuse = 0;
+                return 0;
+        }
+        total_pages_to_unuse = total_pages - target_pages;
+        return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
+}
+
 /*
  * Frontswap, like a true swap device, may unnecessarily retain pages
  * under certain circumstances; "shrink" frontswap is essentially a
@@ -275,10 +293,8 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
  */
 void frontswap_shrink(unsigned long target_pages)
 {
-        unsigned long total_pages = 0, total_pages_to_unuse;
         unsigned long pages_to_unuse = 0;
         int type, ret;
-        bool locked = false;
 
         /*
          * we don't want to hold swap_lock while doing a very
@@ -286,20 +302,10 @@ void frontswap_shrink(unsigned long target_pages)
          * so restart scan from swap_list.head each time
          */
         spin_lock(&swap_lock);
-        locked = true;
-        total_pages = __frontswap_curr_pages();
-        if (total_pages <= target_pages)
-                goto out;
-        total_pages_to_unuse = total_pages - target_pages;
-        ret = __frontswap_unuse_pages(total_pages_to_unuse, &pages_to_unuse, &type);
-        if (ret < 0)
-                goto out;
-        locked = false;
+        ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
         spin_unlock(&swap_lock);
-        try_to_unuse(type, true, pages_to_unuse);
-out:
-        if (locked)
-                spin_unlock(&swap_lock);
+        if (ret == 0 && pages_to_unuse)
+                try_to_unuse(type, true, pages_to_unuse);
         return;
 }
 EXPORT_SYMBOL(frontswap_shrink);