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") 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 Signed-off-by: Greg Kroah-Hartman gregkh@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;