[PATCH] Drivers: hv: vmbus: Add mutex lock to channel show functions

Dexuan Cui decui at microsoft.com
Fri Feb 1 18:24:24 UTC 2019


> From: Kimberly Brown <kimbrownkd at gmail.com>
> Sent: Thursday, January 31, 2019 9:47 AM
> ...
> 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.
Hi Kim,
Can you please share more details about the deadlock? 
It's unclear to me how the deadlock happens.

> 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.
It looks more like a workaround. IMO we should try to find a real fix. :-)
 
> 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

Thanks,
-- Dexuan


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