netdev - RE: Kernel 4.6.7-rt14 kernel workqueue lockup - rtnl deadlock plus syscall endless loop

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Message-ID: <AM5PR0701MB18732AA38AAB6E39A92FA6E3A07F0@AM5PR0701MB1873.eurprd07.prod.outlook.com>
Date:   Wed, 18 Jan 2017 09:57:08 +0000
From:   Elad Nachman <EladN@...at.com>
To:     David Miller <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: Kernel 4.6.7-rt14 kernel workqueue lockup - rtnl deadlock plus
 syscall endless loop

OK, how about reflecting the state of the rtnl lock to user space via the /proc file system?

This way I can test it before using sysctl on the relevant proc files to avoid live-lock.

Thanks,

Elad.

-----Original Message-----
From: David Miller [mailto:davem@...emloft.net]
Sent: יום ג 17 ינואר 2017 21:06
To: Elad Nachman <EladN@...at.com>
Cc: netdev@...r.kernel.org
Subject: Re: Kernel 4.6.7-rt14 kernel workqueue lockup - rtnl deadlock plus syscall endless loop

From: Elad Nachman <EladN@...at.com>
Date: Tue, 17 Jan 2017 18:15:19 +0000

> Any thought about limiting the amount of busy polling?  Say if more
> than X polls are done within a jiffy, then at least for preemptable
> kernels you can sleep for a jiffy inside the syscall to yield the
> CPU for a while?

We cannot yield there, because we must return immediately from this
context in order to drop the sysctl locks and references.
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