From: Jan Kara jack@suse.cz Subject: 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/20190116131217.7226-1-jack@suse.cz Fixes: 89cb0888ca14 "mm: migrate: provide buffer_migrate_page_norefs()" Signed-off-by: Jan Kara jack@suse.cz Cc: Sergey Senozhatsky sergey.senozhatsky.work@gmail.com Cc: Pavel Machek pavel@ucw.cz Cc: Mel Gorman mgorman@techsingularity.net Cc: Vlastimil Babka vbabka@suse.cz Cc: Andrea Arcangeli aarcange@redhat.com Cc: David Rientjes rientjes@google.com Cc: Michal Hocko mhocko@kernel.org Cc: Zi Yan zi.yan@cs.rutgers.edu Cc: Johannes Weiner hannes@cmpxchg.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/migrate.c | 5 ----- 1 file changed, 5 deletions(-)

--- a/mm/migrate.c~mm-migrate-make-buffer_migrate_page_norefs-actually-succeed +++ a/mm/migrate.c @@ -709,7 +709,6 @@ static bool buffer_migrate_lock_buffers( /* 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(

/* 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); _