| Message ID | 20221006134927.41437-4-manivannan.sadhasivam@linaro.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Lorenzo Pieralisi |
| Headers | show |
| Series | PCI: endpoint: Rework the EPC to EPF notification | expand |
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; >
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;
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> --- drivers/pci/endpoint/pci-epc-core.c | 9 +++++---- include/linux/pci-epc.h | 2 ++ 2 files changed, 7 insertions(+), 4 deletions(-)