git: 38c183326425 - main - libusb: dequeue next transfer on completion to prevent stalls

The branch main has been updated by bapt:

URL: https://cgit.FreeBSD.org/src/commit/?id=38c18332642500fdfe075a82f88e033f6673a53f

commit 38c18332642500fdfe075a82f88e033f6673a53f
Author:     Baptiste Daroussin <bapt@FreeBSD.org>
AuthorDate: 2026-02-15 18:07:07 +0000
Commit:     Baptiste Daroussin <bapt@FreeBSD.org>
CommitDate: 2026-02-16 08:14:05 +0000

    libusb: dequeue next transfer on completion to prevent stalls
    
    The transfer proxy callbacks (bulk/interrupt, control, isochronous)
    only called libusb10_submit_transfer_sub() in the START path to
    pipeline the second kernel transfer slot. On completion or error,
    no attempt was made to dequeue the next pending transfer from
    tr_head onto the now-free slot.
    
    When more than two async transfers were submitted on the same
    endpoint, the third (and subsequent) transfers would remain stuck
    on tr_head indefinitely, since no completion ever triggered their
    submission. This caused a protocol-level deadlock in applications
    like adb that submit header + payload + zero-length terminator as
    three separate bulk transfers in sequence.
    
    Fix by calling libusb10_submit_transfer_sub() after every
    libusb10_complete_transfer() in all three proxy callbacks.
    
    MFC After:      2 weeks
    Reviewed by:    adrian
    Differential Revision:  https://reviews.freebsd.org/D55289
---
 lib/libusb/libusb10.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/lib/libusb/libusb10.c b/lib/libusb/libusb10.c
index e226def0b7b6..b3af017ab980 100644
--- a/lib/libusb/libusb10.c
+++ b/lib/libusb/libusb10.c
@@ -1259,6 +1259,9 @@ libusb10_isoc_proxy(struct libusb20_transfer *pxfer)
 			    libusb20_tr_get_length(pxfer, i);
 		}
 		libusb10_complete_transfer(pxfer, sxfer, LIBUSB_TRANSFER_COMPLETED);
+
+		/* start next queued transfer, if any */
+		libusb10_submit_transfer_sub(libusb20_tr_get_priv_sc0(pxfer), uxfer->endpoint);
 		break;
 	case LIBUSB20_TRANSFER_START:
 		/* setup length(s) */
@@ -1281,6 +1284,9 @@ libusb10_isoc_proxy(struct libusb20_transfer *pxfer)
 		break;
 	default:
 		libusb10_complete_transfer(pxfer, sxfer, libusb10_convert_error(status));
+
+		/* start next queued transfer, if any */
+		libusb10_submit_transfer_sub(libusb20_tr_get_priv_sc0(pxfer), uxfer->endpoint);
 		break;
 	}
 }
@@ -1322,11 +1328,15 @@ libusb10_bulk_intr_proxy(struct libusb20_transfer *pxfer)
 			} else {
 				libusb10_complete_transfer(pxfer, sxfer, LIBUSB_TRANSFER_COMPLETED);
 			}
+			/* start next queued transfer, if any */
+			libusb10_submit_transfer_sub(libusb20_tr_get_priv_sc0(pxfer), uxfer->endpoint);
 			break;
 		}
 		/* check for end of data */
 		if (sxfer->rem_len == 0) {
 			libusb10_complete_transfer(pxfer, sxfer, LIBUSB_TRANSFER_COMPLETED);
+			/* start next queued transfer, if any */
+			libusb10_submit_transfer_sub(libusb20_tr_get_priv_sc0(pxfer), uxfer->endpoint);
 			break;
 		}
 		/* FALLTHROUGH */
@@ -1353,6 +1363,8 @@ libusb10_bulk_intr_proxy(struct libusb20_transfer *pxfer)
 
 	default:
 		libusb10_complete_transfer(pxfer, sxfer, libusb10_convert_error(status));
+		/* start next queued transfer, if any */
+		libusb10_submit_transfer_sub(libusb20_tr_get_priv_sc0(pxfer), uxfer->endpoint);
 		break;
 	}
 }
@@ -1397,11 +1409,15 @@ libusb10_ctrl_proxy(struct libusb20_transfer *pxfer)
 			} else {
 				libusb10_complete_transfer(pxfer, sxfer, LIBUSB_TRANSFER_COMPLETED);
 			}
+			/* start next queued transfer, if any */
+			libusb10_submit_transfer_sub(libusb20_tr_get_priv_sc0(pxfer), uxfer->endpoint);
 			break;
 		}
 		/* check for end of data */
 		if (sxfer->rem_len == 0) {
 			libusb10_complete_transfer(pxfer, sxfer, LIBUSB_TRANSFER_COMPLETED);
+			/* start next queued transfer, if any */
+			libusb10_submit_transfer_sub(libusb20_tr_get_priv_sc0(pxfer), uxfer->endpoint);
 			break;
 		}
 		/* FALLTHROUGH */
@@ -1442,6 +1458,8 @@ libusb10_ctrl_proxy(struct libusb20_transfer *pxfer)
 
 	default:
 		libusb10_complete_transfer(pxfer, sxfer, libusb10_convert_error(status));
+		/* start next queued transfer, if any */
+		libusb10_submit_transfer_sub(libusb20_tr_get_priv_sc0(pxfer), uxfer->endpoint);
 		break;
 	}
 }