linux-kernel - [PATCH AUTOSEL 4.14 048/167] vfio-ccw: Do not call flush

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Date:   Wed, 22 May 2019 15:26:43 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Farhan Ali <alifm@...ux.ibm.com>,
        Eric Farman <farman@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Sasha Levin <sashal@...nel.org>, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 048/167] vfio-ccw: Do not call flush_workqueue while holding the spinlock

From: Farhan Ali <alifm@...ux.ibm.com>

[ Upstream commit cea5dde42a83b5f0a039da672f8686455936b8d8 ]

Currently we call flush_workqueue while holding the subchannel
spinlock. But flush_workqueue function can go to sleep, so
do not call the function while holding the spinlock.

Fixes the following bug:

[  285.203430] BUG: scheduling while atomic: bash/14193/0x00000002
[  285.203434] INFO: lockdep is turned off.
....
[  285.203485] Preemption disabled at:
[  285.203488] [<000003ff80243e5c>] vfio_ccw_sch_quiesce+0xbc/0x120 [vfio_ccw]
[  285.203496] CPU: 7 PID: 14193 Comm: bash Tainted: G        W
....
[  285.203504] Call Trace:
[  285.203510] ([<0000000000113772>] show_stack+0x82/0xd0)
[  285.203514]  [<0000000000b7a102>] dump_stack+0x92/0xd0
[  285.203518]  [<000000000017b8be>] __schedule_bug+0xde/0xf8
[  285.203524]  [<0000000000b95b5a>] __schedule+0x7a/0xc38
[  285.203528]  [<0000000000b9678a>] schedule+0x72/0xb0
[  285.203533]  [<0000000000b9bfbc>] schedule_timeout+0x34/0x528
[  285.203538]  [<0000000000b97608>] wait_for_common+0x118/0x1b0
[  285.203544]  [<0000000000166d6a>] flush_workqueue+0x182/0x548
[  285.203550]  [<000003ff80243e6e>] vfio_ccw_sch_quiesce+0xce/0x120 [vfio_ccw]
[  285.203556]  [<000003ff80245278>] vfio_ccw_mdev_reset+0x38/0x70 [vfio_ccw]
[  285.203562]  [<000003ff802458b0>] vfio_ccw_mdev_remove+0x40/0x78 [vfio_ccw]
[  285.203567]  [<000003ff801a499c>] mdev_device_remove_ops+0x3c/0x80 [mdev]
[  285.203573]  [<000003ff801a4d5c>] mdev_device_remove+0xc4/0x130 [mdev]
[  285.203578]  [<000003ff801a5074>] remove_store+0x6c/0xa8 [mdev]
[  285.203582]  [<000000000046f494>] kernfs_fop_write+0x14c/0x1f8
[  285.203588]  [<00000000003c1530>] __vfs_write+0x38/0x1a8
[  285.203593]  [<00000000003c187c>] vfs_write+0xb4/0x198
[  285.203597]  [<00000000003c1af2>] ksys_write+0x5a/0xb0
[  285.203601]  [<0000000000b9e270>] system_call+0xdc/0x2d8

Signed-off-by: Farhan Ali <alifm@...ux.ibm.com>
Reviewed-by: Eric Farman <farman@...ux.ibm.com>
Reviewed-by: Pierre Morel <pmorel@...ux.ibm.com>
Message-Id: <626bab8bb2958ae132452e1ddaf1b20882ad5a9d.1554756534.git.alifm@...ux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/s390/cio/vfio_ccw_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index d22759eb66407..59eb5e6d9c79d 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -52,9 +52,9 @@ int vfio_ccw_sch_quiesce(struct subchannel *sch)
 
 			wait_for_completion_timeout(&completion, 3*HZ);
 
-			spin_lock_irq(sch->lock);
 			private->completion = NULL;
 			flush_workqueue(vfio_ccw_work_q);
+			spin_lock_irq(sch->lock);
 			ret = cio_cancel_halt_clear(sch, &iretry);
 		};
 
-- 
2.20.1