Messages in this thread | | | Date | Thu, 31 Jan 2019 12:47:07 -0500 | From | Kimberly Brown <> | Subject | Re: [PATCH] Drivers: hv: vmbus: Add mutex lock to channel show functions |
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On Thu, Jan 31, 2019 at 04:45:35PM +0000, Michael Kelley wrote: > From: Sasha Levin <sashal@kernel.org> Sent: Thursday, January 31, 2019 7:20 AM > > > > I've queued this one for hyper-fixes, thanks all! > > > > Actually, please hold off on queuing this one. In a conversation I had yesterday with Kim, they had identified a deadlock. Kim was going to be looking at some revisions to avoid the deadlock. > > Kim -- please confirm. > > Michael
This is correct. I need to send a v2 of this patch which addresses two issues:
1) Check channel->state inside the mutex acquire/release in vmbus_chan_attr_show().
2) Prevent a deadlock that can occur between the proposed mutex_lock() call in the vmbus_chan_attr_show() function and the sysfs/kernfs functions.
I've identified two possible solutions to the deadlock:
1) Add a new mutex to the vmbus_channel struct which protects changes to "channel->state". Use this new mutex in vmbus_chan_attr_show() instead of "vmbus_connection.channel_mutex".
2) Use "vmbus_connection.channel_mutex" in vmbus_chan_attr_show() as originally proposed, and acquire it with mutex_trylock(). If the mutex cannot be acquired, return -EINVAL.
I'm leaning towards (2), using mutex_trylock(). "vmbus_connection.channel_mutex" appears to be used only when a channel is being opened or closed, so vmbus_chan_attr_show() should be able to acquire the mutex when the channel is in use.
If anyone has suggestions, please let me know.
Thanks, Kim
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