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Fix polling transfer restart after InterruptStop #119

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merged 1 commit into from
Oct 29, 2023
Merged

Fix polling transfer restart after InterruptStop #119

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21 changes: 10 additions & 11 deletions src/ccid_usb.c
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Original file line number Diff line number Diff line change
Expand Up @@ -113,12 +113,11 @@ typedef struct
*/
_ccid_descriptor ccid;

/* whether the polling should be terminated */
_Atomic bool terminated;

/* libusb transfer for the polling (or NULL) */
pthread_mutex_t polling_transfer_mutex;
struct libusb_transfer *polling_transfer;
/* whether the polling should be terminated */
bool terminate_requested;

/* pointer to the multislot extension (if any) */
struct usbDevice_MultiSlot_Extension *multislot_extension;
Expand Down Expand Up @@ -745,9 +744,9 @@ status_t OpenUSBByName(unsigned int reader_index, /*@null@*/ char *device)
usbDevice[reader_index].interface = interface;
usbDevice[reader_index].real_nb_opened_slots = 1;
usbDevice[reader_index].nb_opened_slots = &usbDevice[reader_index].real_nb_opened_slots;
atomic_init(&usbDevice[reader_index].terminated, false);
pthread_mutex_init(&usbDevice[reader_index].polling_transfer_mutex, NULL);
usbDevice[reader_index].polling_transfer = NULL;
usbDevice[reader_index].terminate_requested = false;
usbDevice[reader_index].disconnected = false;

/* CCID common information */
Expand Down Expand Up @@ -1534,13 +1533,14 @@ int InterruptRead(int reader_index, int timeout /* in ms */)

pthread_mutex_lock(&usbDevice[reader_index].polling_transfer_mutex);
usbDevice[reader_index].polling_transfer = transfer;
bool terminate_requested = usbDevice[reader_index].terminate_requested;
usbDevice[reader_index].terminate_requested = false;
pthread_mutex_unlock(&usbDevice[reader_index].polling_transfer_mutex);

// The termination might've been requested by the other thread before the
// polling_transfer field was written. In that case, we have to cancel the
// transfer here as opposed to InterruptStop().
bool terminated = atomic_load(&usbDevice[reader_index].terminated);
if (terminated) {
if (terminate_requested) {
libusb_cancel_transfer(transfer);
}

Expand Down Expand Up @@ -1608,11 +1608,6 @@ void InterruptStop(int reader_index)
return;
}

// Set the termination flag to handle the case in which the polling_transfer
// value read below is null. The order of operations is important, and it has
// to be opposite to the one in InterruptRead() to avoid race conditions.
atomic_store(&usbDevice[reader_index].terminated, true);

pthread_mutex_lock(&usbDevice[reader_index].polling_transfer_mutex);
if (usbDevice[reader_index].polling_transfer)
{
Expand All @@ -1622,6 +1617,10 @@ void InterruptStop(int reader_index)
if (ret < 0)
DEBUG_CRITICAL2("libusb_cancel_transfer failed: %s",
libusb_error_name(ret));
} else {
// Indicate that the next attempt to start an interrupt transfer shouldn't
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The potential problem is whether it's possible that InterruptStop() is called after the corresponding InterruptRead() already exited; in that case we'll incorrectly abort the next polling transfer later.

If that's possible indeed, I'm not 100% sure what should be the proper fix.

// be proceeded.
usbDevice[reader_index].terminate_requested = true;
}
pthread_mutex_unlock(&usbDevice[reader_index].polling_transfer_mutex);
} /* InterruptStop */
Expand Down