From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from szxga01-in.huawei.com ([119.145.14.64]:18965 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752911Ab2ISGoL (ORCPT ); Wed, 19 Sep 2012 02:44:11 -0400 Message-ID: <50596951.8010000@huawei.com> Date: Wed, 19 Sep 2012 14:42:25 +0800 From: Yijing Wang MIME-Version: 1.0 To: Huang Ying CC: Bjorn Helgaas , Chen Gong , , Hanjun Guo , Subject: Re: [PATCH 2/6] PCI/AER: introduce pci_bus_ops_get() function to avoid a small race condition window References: <1348022442-7816-1-git-send-email-wangyijing@huawei.com> <1348022442-7816-3-git-send-email-wangyijing@huawei.com> <1348033973.8212.132.camel@yhuang-dev> In-Reply-To: <1348033973.8212.132.camel@yhuang-dev> Content-Type: text/plain; charset="UTF-8" Sender: linux-pci-owner@vger.kernel.org List-ID: On 2012/9/19 13:52, Huang Ying wrote: > On Wed, 2012-09-19 at 10:40 +0800, Yijing Wang wrote: >> When we rmmod aer_inject module, there is a race condition window between pci_bus_ops_pop() >> and pci_bus_set_ops() in aer_inject_exit, eg. pci_read_aer/pci_write_aer was called between >> them. So introduce pci_bus_ops_get() to avoid this. >> >> Signed-off-by: Yijing Wang >> --- >> drivers/pci/pcie/aer/aer_inject.c | 21 ++++++++++++++++++--- >> 1 files changed, 18 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/pci/pcie/aer/aer_inject.c b/drivers/pci/pcie/aer/aer_inject.c >> index 0f00a27..442147b 100644 >> --- a/drivers/pci/pcie/aer/aer_inject.c >> +++ b/drivers/pci/pcie/aer/aer_inject.c >> @@ -67,6 +67,8 @@ struct pci_bus_ops { >> struct pci_ops *ops; >> }; >> >> +#define to_pci_bus_ops(n) container_of(n, struct pci_bus_ops, list) >> + >> static LIST_HEAD(einjected); >> >> static LIST_HEAD(pci_bus_ops_list); >> @@ -160,6 +162,18 @@ static struct pci_bus_ops *pci_bus_ops_pop(void) >> return bus_ops; >> } >> >> +static struct pci_bus_ops *pci_bus_ops_get(struct pci_bus_ops *from) >> +{ >> + struct pci_bus_ops *bus_ops = NULL; >> + struct list_head *n; >> + >> + n = from ? from->list.next : pci_bus_ops_list.next; >> + if (n != &pci_bus_ops_list) >> + bus_ops = to_pci_bus_ops(n); >> + >> + return bus_ops; >> +} >> + >> static u32 *find_pci_config_dword(struct aer_error *err, int where, >> int *prw1cs) >> { >> @@ -540,14 +554,15 @@ static void __exit aer_inject_exit(void) >> { >> struct aer_error *err, *err_next; >> unsigned long flags; >> - struct pci_bus_ops *bus_ops; >> + struct pci_bus_ops *bus_ops = NULL; >> >> misc_deregister(&aer_inject_device); >> >> - while ((bus_ops = pci_bus_ops_pop())) { >> + while ((bus_ops = pci_bus_ops_get(bus_ops))) >> pci_bus_set_ops(bus_ops->bus, bus_ops->ops); > > In fact, this is > > list_for_each_entry(&pci_bus_ops_list) > pci_bus_set_ops() > > Because we are in module exit path, there will be no new user of > pci_bus_ops_list, it appears safe to do that without lock. > > But the bus_ops may be deleted from the list when accessed via > pci_ops_aer. So It may be better to wait for all pci_ops_aer functions Hi Huang Ying, I have some confusions about this, can you explain this? Thanks very much! In my idea, if pci_ops_aer be called, it hold the pci_lock, so pci_bus_set_ops will wait for pci_ops_aer functions to exit.So in my idea, after pci_bus_set_ops loop completed. pci_ops_aer functions have been exit, and will never be called again(because all pci_ops_aer). > return before delete them. synchronize_rcu() should be sufficient for > that, because all pci_ops_aer functions are called with spinlock held. > > Best Regards, > Huang Ying > >> + >> + while ((bus_ops = pci_bus_ops_pop())) >> kfree(bus_ops); >> - } >> >> spin_lock_irqsave(&inject_lock, flags); >> list_for_each_entry_safe(err, err_next, &einjected, list) { > > > > . > -- Thanks! Yijing