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Subject[PATCH 4.19 108/276] vfio-ccw: Do not call flush_workqueue while holding the spinlock
Date
[ 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@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Message-Id: <626bab8bb2958ae132452e1ddaf1b20882ad5a9d.1554756534.git.alifm@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.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 fabd9798e4c47..0e0a743aeaf69 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -54,9 +54,9 @@ 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


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