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Commit 6956c0e3 authored by Farhan Ali's avatar Farhan Ali Committed by Greg Kroah-Hartman
Browse files

vfio-ccw: Prevent quiesce function going into an infinite loop 



[ Upstream commit d1ffa760d22aa1d8190478e5ef555c59a771db27 ]

The quiesce function calls cio_cancel_halt_clear() and if we
get an -EBUSY we go into a loop where we:
	- wait for any interrupts
	- flush all I/O in the workqueue
	- retry cio_cancel_halt_clear

During the period where we are waiting for interrupts or
flushing all I/O, the channel subsystem could have completed
a halt/clear action and turned off the corresponding activity
control bits in the subchannel status word. This means the next
time we call cio_cancel_halt_clear(), we will again start by
calling cancel subchannel and so we can be stuck between calling
cancel and halt forever.

Rather than calling cio_cancel_halt_clear() immediately after
waiting, let's try to disable the subchannel. If we succeed in
disabling the subchannel then we know nothing else can happen
with the device.

Suggested-by: default avatarEric Farman <farman@linux.ibm.com>
Signed-off-by: default avatarFarhan Ali <alifm@linux.ibm.com>
Message-Id: <4d5a4b98ab1b41ac6131b5c36de18b76c5d66898.1555449329.git.alifm@linux.ibm.com>
Reviewed-by: default avatarEric Farman <farman@linux.ibm.com>
Acked-by: default avatarHalil Pasic <pasic@linux.ibm.com>
Signed-off-by: default avatarCornelia Huck <cohuck@redhat.com>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 476e87eb

drivers/s390/cio/vfio_ccw_drv.c

+18 −14
Original line number Diff line number Diff line
@@ -40,11 +40,17 @@ int vfio_ccw_sch_quiesce(struct subchannel *sch) 
	if (ret != -EBUSY)

		goto out_unlock;



	do {

	iretry = 255;

	do {



		ret = cio_cancel_halt_clear(sch, &iretry);

		while (ret == -EBUSY) {



		if (ret == -EIO) {

			pr_err("vfio_ccw: could not quiesce subchannel 0.%x.%04x!\n",

			       sch->schid.ssid, sch->schid.sch_no);

			break;

		}



		/*

		 * Flush all I/O and wait for

		 * cancel/halt/clear completion.
@@ -52,14 +58,12 @@ int vfio_ccw_sch_quiesce(struct subchannel *sch) 
		private->completion = &completion;

		spin_unlock_irq(sch->lock);



		if (ret == -EBUSY)

			wait_for_completion_timeout(&completion, 3*HZ);



		private->completion = NULL;

		flush_workqueue(vfio_ccw_work_q);

		spin_lock_irq(sch->lock);

			ret = cio_cancel_halt_clear(sch, &iretry);

		};



		ret = cio_disable_subchannel(sch);

	} while (ret == -EBUSY);

out_unlock: