[PATCH 4.4 20/73] btrfs: start readahead also in seed devices

[Greg Kroah-Hartman]

From: Naohiro Aota <naohiro.aota@xxxxxxx>

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: stable@xxxxxxxxxxxxxxx # 3.2+: ce7791ffee1e: Btrfs: fix race between readahead and device replace/removal
Cc: stable@xxxxxxxxxxxxxxx # 3.2+
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -762,6 +762,7 @@ static void __reada_start_machine(struct
 	u64 total = 0;
 	int i;
 
+again:
 	do {
 		enqueued = 0;
 		mutex_lock(&fs_devices->device_list_mutex);
@@ -774,6 +775,10 @@ 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;