From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [Pv-ops][PATCH] Netback multiple tasklet support Date: Thu, 10 Dec 2009 09:54:20 -0800 Message-ID: <4B2135CC.6000004@goop.org> References: <4FA716B1526C7C4DB0375C6DADBC4EA342A7A7E951@LONPMAILBOX01.citrite.net> <4FA716B1526C7C4DB0375C6DADBC4EA342A7A7E95E@LONPMAILBOX01.citrite.net> <4B182D87.6030901@goop.org> <4B187513.80003@goop.org> <4B200727.8040000@goop.org> <1260436078.23698.45463.camel@zakaz.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1260436078.23698.45463.camel@zakaz.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ian Campbell Cc: Steven Smith , "Xu, Dongxiao" , "xen-devel@lists.xensource.com" , Ian Pratt List-Id: xen-devel@lists.xenproject.org On 12/10/09 01:07, Ian Campbell wrote: > Subject: xen: ensure locking gnttab_copy_grant_page is safe against interrupts. > > Now that netback processing occurs in a thread instead of a tasklet > gnttab_copy_grant_page needs to be safe against interrupts. > > The code is currently commented out in this tree but on 2.6.18 we observed a > deadlock where the netback thread called gnttab_copy_grant_page, locked > gnttab_dma_lock for writing, was interrupted and on return from interrupt the > network stack's TX tasklet ended up calling __gnttab_dma_map_page via the > hardware driver->swiotlb and tries to take gnttab_dma_lock for reading. > > Correct the commented code so we don't get bitten if/when it is re-enabled. > What's the issue here? I'm inclined to just remove the commented-out code if it isn't being used, and re-evaluate the locking if/when it becomes necessary. J