[PATCH] f2fs: fix to avoid discard command leak

[Chao Yu]

 =============================================================================
 BUG discard_cmd (Tainted: G    B      OE  ): Objects remaining in discard_cmd on __kmem_cache_shutdown()
 -----------------------------------------------------------------------------

 INFO: Slab 0xffffe1ac481d22c0 objects=36 used=2 fp=0xffff936b4748bf50 flags=0x2ffff0000000100
 Call Trace:
  dump_stack+0x63/0x87
  slab_err+0xa1/0xb0
  __kmem_cache_shutdown+0x183/0x390
  shutdown_cache+0x14/0x110
  kmem_cache_destroy+0x195/0x1c0
  f2fs_destroy_segment_manager_caches+0x21/0x40 [f2fs]
  exit_f2fs_fs+0x35/0x641 [f2fs]
  SyS_delete_module+0x155/0x230
  ? vtime_user_exit+0x29/0x70
  do_syscall_64+0x6e/0x160
  entry_SYSCALL64_slow_path+0x25/0x25

 INFO: Object 0xffff936b4748b000 @offset=0
 INFO: Object 0xffff936b4748b070 @offset=112
 kmem_cache_destroy discard_cmd: Slab cache still has objects
 Call Trace:
  dump_stack+0x63/0x87
  kmem_cache_destroy+0x1b4/0x1c0
  f2fs_destroy_segment_manager_caches+0x21/0x40 [f2fs]
  exit_f2fs_fs+0x35/0x641 [f2fs]
  SyS_delete_module+0x155/0x230
  do_syscall_64+0x6e/0x160
  entry_SYSCALL64_slow_path+0x25/0x25

Recovery can cache discard commands, so in error path of fill_super(),
we need give a chance to handle them, otherwise it will lead to leak
of discard_cmd slab cache.

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 fs/f2fs/segment.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 57a83a68ae03..449ef70d99cc 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2084,6 +2084,13 @@ static void destroy_discard_cmd_control(struct f2fs_sb_info *sbi)
 
 	f2fs_stop_discard_thread(sbi);
 
+	/*
+	 * Recovery can cache discard commands, so in error path of
+	 * fill_super(), it needs to give a chance to handle them.
+	 */
+	if (unlikely(atomic_read(&dcc->discard_cmd_cnt)))
+		f2fs_issue_discard_timeout(sbi);
+
 	kvfree(dcc);
 	SM_I(sbi)->dcc_info = NULL;
 }
-- 
2.18.0.rc1