Messages in this thread | | | Subject | Re: [PATCH v3 3/5] PCI: endpoint: Use a separate lock for protecting epc->pci_epf list | From | Kishon Vijay Abraham I <> | Date | Tue, 11 Oct 2022 18:10:08 +0530 |
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On 06/10/22 7:19 pm, Manivannan Sadhasivam wrote: > The EPC controller maintains a list of EPF drivers added to it. For > protecting this list against the concurrent accesses, the epc->lock > (used for protecting epc_ops) has been used so far. Since there were > no users trying to use epc_ops and modify the pci_epf list simultaneously, > this was not an issue. > > But with the addition of callback mechanism for passing the events, this > will be a problem. Because the pci_epf list needs to be iterated first > for getting hold of the EPF driver and then the relevant event specific > callback needs to be called for the driver. > > If the same epc->lock is used, then it will result in a deadlock scenario. > > For instance, > > ... > mutex_lock(&epc->lock); > list_for_each_entry(epf, &epc->pci_epf, list) { > epf->event_ops->core_init(epf); > | > |-> pci_epc_set_bar(); > | > |-> mutex_lock(&epc->lock) # DEADLOCK > ... > > So to fix this issue, use a separate lock called "list_lock" for > protecting the pci_epf list against the concurrent accesses. This lock > will also be used by the callback mechanism. > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com> > --- > drivers/pci/endpoint/pci-epc-core.c | 9 +++++---- > include/linux/pci-epc.h | 2 ++ > 2 files changed, 7 insertions(+), 4 deletions(-) > > diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c > index 3bc9273d0a08..6cce430d431b 100644 > --- a/drivers/pci/endpoint/pci-epc-core.c > +++ b/drivers/pci/endpoint/pci-epc-core.c > @@ -613,7 +613,7 @@ int pci_epc_add_epf(struct pci_epc *epc, struct pci_epf *epf, > if (type == SECONDARY_INTERFACE && epf->sec_epc) > return -EBUSY; > > - mutex_lock(&epc->lock); > + mutex_lock(&epc->list_lock); > func_no = find_first_zero_bit(&epc->function_num_map, > BITS_PER_LONG); > if (func_no >= BITS_PER_LONG) { > @@ -640,7 +640,7 @@ int pci_epc_add_epf(struct pci_epc *epc, struct pci_epf *epf, > > list_add_tail(list, &epc->pci_epf); > ret: > - mutex_unlock(&epc->lock); > + mutex_unlock(&epc->list_lock); > > return ret; > } > @@ -672,11 +672,11 @@ void pci_epc_remove_epf(struct pci_epc *epc, struct pci_epf *epf, > list = &epf->sec_epc_list; > } > > - mutex_lock(&epc->lock); > + mutex_lock(&epc->list_lock); > clear_bit(func_no, &epc->function_num_map); > list_del(list); > epf->epc = NULL; > - mutex_unlock(&epc->lock); > + mutex_unlock(&epc->list_lock); > } > EXPORT_SYMBOL_GPL(pci_epc_remove_epf); > > @@ -773,6 +773,7 @@ __pci_epc_create(struct device *dev, const struct pci_epc_ops *ops, > } > > mutex_init(&epc->lock); > + mutex_init(&epc->list_lock); > INIT_LIST_HEAD(&epc->pci_epf); > ATOMIC_INIT_NOTIFIER_HEAD(&epc->notifier); > > diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h > index a48778e1a4ee..fe729dfe509b 100644 > --- a/include/linux/pci-epc.h > +++ b/include/linux/pci-epc.h > @@ -122,6 +122,7 @@ struct pci_epc_mem { > * struct pci_epc - represents the PCI EPC device > * @dev: PCI EPC device > * @pci_epf: list of endpoint functions present in this EPC device > + * list_lock: Mutex for protecting pci_epf list > * @ops: function pointers for performing endpoint operations > * @windows: array of address space of the endpoint controller > * @mem: first window of the endpoint controller, which corresponds to > @@ -139,6 +140,7 @@ struct pci_epc_mem { > struct pci_epc { > struct device dev; > struct list_head pci_epf; > + struct mutex list_lock; > const struct pci_epc_ops *ops; > struct pci_epc_mem **windows; > struct pci_epc_mem *mem; >
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