[PATCH 4.14 39/51] btrfs: start readahead also in seed devices

[Greg Kroah-Hartman]

From: Naohiro Aota <naohiro.a...@wdc.com>

commit c4e0540d0ad49c8ceab06cceed1de27c4fe29f6e upstream.

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+
Reviewed-by: Filipe Manana <fdman...@suse.com>
Signed-off-by: Naohiro Aota <naohiro.a...@wdc.com>
Signed-off-by: David Sterba <dste...@suse.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 fs/btrfs/reada.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -759,6 +759,7 @@ static void __reada_start_machine(struct
        u64 total = 0;
        int i;
 
+again:
        do {
                enqueued = 0;
                mutex_lock(&fs_devices->device_list_mutex);
@@ -770,6 +771,10 @@ static void __reada_start_machine(struct
                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;