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PCI: endpoint: Use a separate lock for protecting epc->pci_epf list

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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.

Link: https://lore.kernel.org/linux-pci/20230124071158.5503-4-manivannan.sadhasivam@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
This commit is contained in:
Manivannan Sadhasivam 2023-01-24 12:41:56 +05:30 committed by Krzysztof Wilczyński
parent c2cc5cdda4
commit d6dd5bafaa
No known key found for this signature in database
GPG Key ID: 7C64768D3DE334E7
2 changed files with 7 additions and 4 deletions
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9
drivers/pci/endpoint/pci-epc-core.c
View File

@ -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);
@ -777,6 +777,7 @@ __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);

2
include/linux/pci-epc.h
View File

@ -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;