netdev - RE: [PATCH net RFC 2/2] ixgbe: fix sleep bug caused by napi_disable inside local_bh

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Message-ID: <02874ECE860811409154E81DA85FBB58565F5E52@ORSMSX104.amr.corp.intel.com>
Date:	Thu, 19 Sep 2013 22:28:48 +0000
From:	"Keller, Jacob E" <jacob.e.keller@...el.com>
To:	Francois Romieu <romieu@...zoreil.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Duyck, Alexander H" <alexander.h.duyck@...el.com>,
	Hyong-Youb Kim <hykim@...i.com>,
	"Dmitry Kravkov" <dmitry@...adcom.com>,
	Amir Vadai <amirv@...lanox.com>,
	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
Subject: RE: [PATCH net RFC 2/2] ixgbe: fix sleep bug caused by napi_disable
 inside local_bh_disable()d context

> -----Original Message-----
> From: Francois Romieu [mailto:romieu@...zoreil.com]
> Sent: Thursday, September 19, 2013 2:33 PM
> To: Keller, Jacob E
> Cc: netdev@...r.kernel.org; Duyck, Alexander H; Hyong-Youb Kim;
> Dmitry Kravkov; Amir Vadai; Eliezer Tamir
> Subject: Re: [PATCH net RFC 2/2] ixgbe: fix sleep bug caused by
> napi_disable inside local_bh_disable()d context
> 
> Keller, Jacob E <jacob.e.keller@...el.com> :
> [...]
> > I know that we need local_bh_disable around the qv_lock_napi code
> because
> > it uses spin_lock instead of spin_lock_bh. I believe the reason we need
> bh
> > disabled around the entire context is so that the small window between
> > failed calls to qv_lock_napi don't get interrupted and continue to have
> > busy_poll lock the q_vector over and over.
> 
> Thanks for explaining the intent. I'll do my homework.
> 

Thanks. Again, I am not entirely sure this is the right solution, (hence the RFC) because I am not that familiar with the code here.

> > I have to move the local_bh_disable in order to put napi_disable
> outside
> > of the call since napi_disable could sleep, causing a scheduling while
> > atomic BUG.
> 
> I am in violent agreement with this part.
> --
> Ueimor

Regards,
Jake
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