mm: migrate: make buffer_migrate_page_norefs() actually succeed

Currently, buffer_migrate_page_norefs() was constantly failing because
buffer_migrate_lock_buffers() grabbed reference on each buffer.  In
fact, there's no reason for buffer_migrate_lock_buffers() to grab any
buffer references as the page is locked during all our operation and
thus nobody can reclaim buffers from the page.

So remove grabbing of buffer references which also makes
buffer_migrate_page_norefs() succeed.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 89cb0888ca14 "mm: migrate: provide buffer_migrate_page_norefs()"
Signed-off-by: Jan Kara <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/migrate.c b/mm/migrate.c
index a16b15090df3b5f62e8421b16d642db113075eeb..712b231a737699355000bfbace103f3552d3e35d 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -709,7 +709,6 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head,
        /* Simple case, sync compaction */
        if (mode != MIGRATE_ASYNC) {
                do {
-                       get_bh(bh);
                        lock_buffer(bh);
                        bh = bh->b_this_page;
 
@@ -720,18 +719,15 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head,
 
        /* async case, we cannot block on lock_buffer so use trylock_buffer */
        do {
-               get_bh(bh);
                if (!trylock_buffer(bh)) {
                        /*
                         * We failed to lock the buffer and cannot stall in
                         * async migration. Release the taken locks
                         */
                        struct buffer_head *failed_bh = bh;
-                       put_bh(failed_bh);
                        bh = head;
                        while (bh != failed_bh) {
                                unlock_buffer(bh);
-                               put_bh(bh);
                                bh = bh->b_this_page;
                        }
                        return false;
@@ -818,7 +814,6 @@ unlock_buffers:
        bh = head;
        do {
                unlock_buffer(bh);
-               put_bh(bh);
                bh = bh->b_this_page;
 
        } while (bh != head);