[PATCH] btrfs: start readahead also in seed devices

[Naohiro Aota]

Currently, btrfs does not consult seed devices to start readahead. As a
result, if readahead zone is added to the seed devices, btrfs_reada_wait()
indefinitely wait for the reada_ctl to finish.

You can reproduce the hung by modifying btrfs/163 to have larger initial
file size (e.g. xfs_io pwrite 4M instead of current 256K).

Fixes: 7414a03fbf9e ("btrfs: initial readahead code and prototypes")
Cc: sta...@vger.kernel.org # 3.2+: ce7791ffee1e: Btrfs: fix race between 
readahead and device replace/removal
Cc: sta...@vger.kernel.org # 3.2+
Signed-off-by: Naohiro Aota <naohiro.a...@wdc.com>
---
 fs/btrfs/reada.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index 10d9589001a9..bb5bd49573b4 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -747,6 +747,7 @@ static void __reada_start_machine(struct btrfs_fs_info 
*fs_info)
        u64 total = 0;
        int i;
 
+again:
        do {
                enqueued = 0;
                mutex_lock(&fs_devices->device_list_mutex);
@@ -758,6 +759,10 @@ static void __reada_start_machine(struct btrfs_fs_info 
*fs_info)
                mutex_unlock(&fs_devices->device_list_mutex);
                total += enqueued;
        } while (enqueued && total < 10000);
+       if (fs_devices->seed) {
+               fs_devices = fs_devices->seed;
+               goto again;
+       }
 
        if (enqueued == 0)
                return;
-- 
2.21.0