On 2019/06/06 20:14, Filipe Manana wrote:
> On Thu, Jun 6, 2019 at 8:56 AM Naohiro Aota <naohiro.aota@xxxxxxx> wrote:
>>
>> 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).
>
> Are you planning on submitting a patch for the test case as well, so
> that it writes at least 4Mb?
> Would be useful to have.
I will send that patch soon.
Thanks,
>
>>
>> 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+
>> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
>
> Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
>
> Looks good, thanks.
>
>> ---
>> fs/btrfs/reada.c | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
>> index 10d9589001a9..bb5bd49573b4 100644
>> --- a/fs/btrfs/reada.c
>> +++ b/fs/btrfs/reada.c
>> @@ -747,6 +747,7 @@ 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);
>> @@ -758,6 +759,10 @@ 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;
>> --
>> 2.21.0
>>
>
>
