On Wed, 2012-09-19 at 14:42 +0800, Yijing Wang wrote:
> 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 <wangyijing@xxxxxxxxxx>
> >> ---
> >> 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).
Yes. You are right, waiting is not necessary here.
Best Regards,
Huang Ying
> > 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) {
> >
> >
> >
> > .
> >
>
>
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