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Subject[PATCH 3.16 63/87] btrfs: start readahead also in seed devices
3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Naohiro Aota <naohiro.aota@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")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/reada.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -764,6 +764,7 @@ static void __reada_start_machine(struct
u64 total = 0;
int i;

+again:
do {
enqueued = 0;
mutex_lock(&fs_devices->device_list_mutex);
@@ -776,6 +777,10 @@ 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;
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