linux-kernel - [PATCH 14/38] drbd: drbdsetup detach of an unresponsive local disk should not block IO "forever"

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Date:	Wed, 25 Nov 2015 11:53:47 +0100
From:	Philipp Reisner <philipp.reisner@...bit.com>
To:	Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org
Cc:	drbd-dev@...ts.linbit.com
Subject: [PATCH 14/38] drbd: drbdsetup detach of an unresponsive local disk should not block IO "forever"

From: Lars Ellenberg <lars.ellenberg@...bit.com>

When detaching, we make sure no application IO is in-flight
by internally suspending IO, then trigger the state change,
wait for the result, and finally internally resume IO again.

Once we triggered the stat change to "Failed",
we expect it to change from Failed to Diskless.
(To avoid races, we actually wait for it to leave "Failed").

On an unresponsive local IO backend, this may not happen, ever.
Don't have a "hung" detach block IO "forever", but resume IO
before waiting for the state change to Diskless.

We may well be able to continue IO to and from a healthy peer.

Signed-off-by: Philipp Reisner <philipp.reisner@...bit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@...bit.com>
---
 drivers/block/drbd/drbd_nl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index af78f09..331b378 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1929,9 +1929,9 @@ static int adm_detach(struct drbd_device *device, int force)
 	retcode = drbd_request_state(device, NS(disk, D_FAILED));
 	drbd_md_put_buffer(device);
 	/* D_FAILED will transition to DISKLESS. */
+	drbd_resume_io(device);
 	ret = wait_event_interruptible(device->misc_wait,
 			device->state.disk != D_FAILED);
-	drbd_resume_io(device);
 	if ((int)retcode == (int)SS_IS_DISKLESS)
 		retcode = SS_NOTHING_TO_DO;
 	if (ret)
-- 
1.9.1

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