WARN_ON isn't enough, we need to stop the loop if for any reason
we would overrun the devices_info array.

I tried to track down the connection between the length of
the alloc_devices list and the rw_devices counter but
it wasn't immediately obvious, so be defensive about it.

Signed-off-by: Eric Sandeen <sand...@redhat.com>
---
 fs/btrfs/volumes.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 15f6efd..09c63ac 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3630,12 +3630,16 @@ static int __btrfs_alloc_chunk(struct 
btrfs_trans_handle *trans,
                if (max_avail < BTRFS_STRIPE_LEN * dev_stripes)
                        continue;
 
+               if (ndevs == fs_devices->rw_devices) {
+                       WARN(1, "%s: found more than %llu devices\n",
+                            __func__, fs_devices->rw_devices);
+                       break;
+               }
                devices_info[ndevs].dev_offset = dev_offset;
                devices_info[ndevs].max_avail = max_avail;
                devices_info[ndevs].total_avail = total_avail;
                devices_info[ndevs].dev = device;
                ++ndevs;
-               WARN_ON(ndevs > fs_devices->rw_devices);
        }
 
        /*
-- 
1.7.1

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