From 4d5715676e477faf96c876516715a39960ca72d6 Mon Sep 17 00:00:00 2001
From: Naohiro Aota <naohiro.aota@wdc.com>
Date: Thu, 6 Jun 2019 16:54:44 +0900
Subject: btrfs: start readahead also in seed devices
Git-commit: c4e0540d0ad49c8ceab06cceed1de27c4fe29f6e
Patch-mainline: v5.2-rc6
References: bsc#1144886

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@vger.kernel.org # 3.2+: ce7791ffee1e: Btrfs: fix race between readahead and device replace/removal
Cc: stable@vger.kernel.org # 3.2+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/reada.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index a17e775a4a89..ea4d24381c70 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -760,6 +760,7 @@ 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);
@@ -771,6 +772,10 @@ 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;
-- 
2.17.1