releases/3.18.62/fs-dcache.c-fix-spin-lockup-issue-on-nlru-lock.patch

   1 From b17c070fb624cf10162cf92ea5e1ec25cd8ac176 Mon Sep 17 00:00:00 2001
   2 From: Sahitya Tummala <stummala@codeaurora.org>
   3 Date: Mon, 10 Jul 2017 15:50:00 -0700
   4 Subject: fs/dcache.c: fix spin lockup issue on nlru->lock
   5
   6 From: Sahitya Tummala <stummala@codeaurora.org>
   7
   8 commit b17c070fb624cf10162cf92ea5e1ec25cd8ac176 upstream.
   9
  10 __list_lru_walk_one() acquires nlru spin lock (nlru->lock) for longer
  11 duration if there are more number of items in the lru list.  As per the
  12 current code, it can hold the spin lock for upto maximum UINT_MAX
  13 entries at a time.  So if there are more number of items in the lru
  14 list, then "BUG: spinlock lockup suspected" is observed in the below
  15 path:
  16
  17   spin_bug+0x90
  18   do_raw_spin_lock+0xfc
  19   _raw_spin_lock+0x28
  20   list_lru_add+0x28
  21   dput+0x1c8
  22   path_put+0x20
  23   terminate_walk+0x3c
  24   path_lookupat+0x100
  25   filename_lookup+0x6c
  26   user_path_at_empty+0x54
  27   SyS_faccessat+0xd0
  28   el0_svc_naked+0x24
  29
  30 This nlru->lock is acquired by another CPU in this path -
  31
  32   d_lru_shrink_move+0x34
  33   dentry_lru_isolate_shrink+0x48
  34   __list_lru_walk_one.isra.10+0x94
  35   list_lru_walk_node+0x40
  36   shrink_dcache_sb+0x60
  37   do_remount_sb+0xbc
  38   do_emergency_remount+0xb0
  39   process_one_work+0x228
  40   worker_thread+0x2e0
  41   kthread+0xf4
  42   ret_from_fork+0x10
  43
  44 Fix this lockup by reducing the number of entries to be shrinked from
  45 the lru list to 1024 at once.  Also, add cond_resched() before
  46 processing the lru list again.
  47
  48 Link: http://marc.info/?t=149722864900001&r=1&w=2
  49 Link: http://lkml.kernel.org/r/1498707575-2472-1-git-send-email-stummala@codeaurora.org
  50 Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
  51 Suggested-by: Jan Kara <jack@suse.cz>
  52 Suggested-by: Vladimir Davydov <vdavydov.dev@gmail.com>
  53 Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
  54 Cc: Alexander Polakov <apolyakov@beget.ru>
  55 Cc: Al Viro <viro@zeniv.linux.org.uk>
  56 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  57 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  58 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  59
  60 ---
  61  fs/dcache.c |    5 +++--
  62  1 file changed, 3 insertions(+), 2 deletions(-)
  63
  64 --- a/fs/dcache.c
  65 +++ b/fs/dcache.c
  66 @@ -1104,11 +1104,12 @@ void shrink_dcache_sb(struct super_block
  67                 LIST_HEAD(dispose);
  68
  69                 freed = list_lru_walk(&sb->s_dentry_lru,
  70 -                       dentry_lru_isolate_shrink, &dispose, UINT_MAX);
  71 +                       dentry_lru_isolate_shrink, &dispose, 1024);
  72
  73                 this_cpu_sub(nr_dentry_unused, freed);
  74                 shrink_dentry_list(&dispose);
  75 -       } while (freed > 0);
  76 +               cond_resched();
  77 +       } while (list_lru_count(&sb->s_dentry_lru) > 0);
  78  }
  79  EXPORT_SYMBOL(shrink_dcache_sb);
  80