drbd: fix potential deadlock on detach
If we have contention in drbd_al_begin_iod (heavy randon IO),
an administrative request to detach the disk may deadlock
for similar reasons as the recently fixed deadlock if detaching
because of IO-error.
The approach taken here is to either go through the intermediate
cleanup state D_FAILED, or first lock out application io,
don't just go directly to D_DISKLESS.
We need an additional state bit (WAS_IO_ERROR) to distinguish
the -> D_FAILED because of IO-error from other failures.
Sanitize D_ATTACHING -> D_FAILED to D_ATTACHING -> D_DISKLESS.
If only attaching, ldev may be missing still, but would be referenced
from within the after_state_ch for -> D_FAILED, potentially
dereferencing a NULL pointer.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index c498c48..0cba7d3 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -870,6 +870,11 @@
retcode = ERR_DISK_CONFIGURED;
goto fail;
}
+ /* It may just now have detached because of IO error. Make sure
+ * drbd_ldev_destroy is done already, we may end up here very fast,
+ * e.g. if someone calls attach from the on-io-error handler,
+ * to realize a "hot spare" feature (not that I'd recommend that) */
+ wait_event(mdev->misc_wait, !atomic_read(&mdev->local_cnt));
/* allocation not in the IO path, cqueue thread context */
nbc = kzalloc(sizeof(struct drbd_backing_dev), GFP_KERNEL);
@@ -1262,7 +1267,7 @@
force_diskless_dec:
put_ldev(mdev);
force_diskless:
- drbd_force_state(mdev, NS(disk, D_DISKLESS));
+ drbd_force_state(mdev, NS(disk, D_FAILED));
drbd_md_sync(mdev);
release_bdev2_fail:
if (nbc)
@@ -1285,10 +1290,19 @@
return 0;
}
+/* Detaching the disk is a process in multiple stages. First we need to lock
+ * out application IO, in-flight IO, IO stuck in drbd_al_begin_io.
+ * Then we transition to D_DISKLESS, and wait for put_ldev() to return all
+ * internal references as well.
+ * Only then we have finally detached. */
static int drbd_nl_detach(struct drbd_conf *mdev, struct drbd_nl_cfg_req *nlp,
struct drbd_nl_cfg_reply *reply)
{
+ drbd_suspend_io(mdev); /* so no-one is stuck in drbd_al_begin_io */
reply->ret_code = drbd_request_state(mdev, NS(disk, D_DISKLESS));
+ if (mdev->state.disk == D_DISKLESS)
+ wait_event(mdev->misc_wait, !atomic_read(&mdev->local_cnt));
+ drbd_resume_io(mdev);
return 0;
}