queue-4.14/btrfs-start-readahead-also-in-seed-devices.patch

   1 From c4e0540d0ad49c8ceab06cceed1de27c4fe29f6e Mon Sep 17 00:00:00 2001
   2 From: Naohiro Aota <naohiro.aota@wdc.com>
   3 Date: Thu, 6 Jun 2019 16:54:44 +0900
   4 Subject: btrfs: start readahead also in seed devices
   5
   6 From: Naohiro Aota <naohiro.aota@wdc.com>
   7
   8 commit c4e0540d0ad49c8ceab06cceed1de27c4fe29f6e upstream.
   9
  10 Currently, btrfs does not consult seed devices to start readahead. As a
  11 result, if readahead zone is added to the seed devices, btrfs_reada_wait()
  12 indefinitely wait for the reada_ctl to finish.
  13
  14 You can reproduce the hung by modifying btrfs/163 to have larger initial
  15 file size (e.g. xfs_io pwrite 4M instead of current 256K).
  16
  17 Fixes: 7414a03fbf9e ("btrfs: initial readahead code and prototypes")
  18 Cc: stable@vger.kernel.org # 3.2+: ce7791ffee1e: Btrfs: fix race between readahead and device replace/removal
  19 Cc: stable@vger.kernel.org # 3.2+
  20 Reviewed-by: Filipe Manana <fdmanana@suse.com>
  21 Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
  22 Signed-off-by: David Sterba <dsterba@suse.com>
  23 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  24
  25 ---
  26  fs/btrfs/reada.c |    5 +++++
  27  1 file changed, 5 insertions(+)
  28
  29 --- a/fs/btrfs/reada.c
  30 +++ b/fs/btrfs/reada.c
  31 @@ -759,6 +759,7 @@ static void __reada_start_machine(struct
  32         u64 total = 0;
  33         int i;
  34
  35 +again:
  36         do {
  37                 enqueued = 0;
  38                 mutex_lock(&fs_devices->device_list_mutex);
  39 @@ -770,6 +771,10 @@ static void __reada_start_machine(struct
  40                 mutex_unlock(&fs_devices->device_list_mutex);
  41                 total += enqueued;
  42         } while (enqueued && total < 10000);
  43 +       if (fs_devices->seed) {
  44 +               fs_devices = fs_devices->seed;
  45 +               goto again;
  46 +       }
  47
  48         if (enqueued == 0)
  49                 return;