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.
>
> 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
>
--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
