Package: libusb Version: 1.0.6-1~bpo50+1 Severity: normal One of my programs uses libusb. Among other things, it listens for hotplug events via a uevent socket, and after receiving one, calls libusb_get_device_list() to list the USB devices and handle those I'm interested in. Between the hotplug event and the call to libusb_get_device_list() there may be some delay (which may or may not be relevant to causing the bug) while the program does other things.
The problem is that libusb_get_device_list() sometimes fails at some point, i.e. returns 0, and keeps doing so for the rest of the program run. It is not easy to reproduce. It typically occurs after I plug and unplug some USB devices quickly and/or often. Since I can't give a procedure to reproduce it, I did some debugging with gdb, and I found that before the error occurs, the program reaches line 939 (in this version) in sysfs_scan_device(): sysfs_can_relate_devices = 0; At this point filename == "/sys/bus/usb/devices/1-1/busnum" which is a valid path at this moment. Since this line should be executed only if opening filename failed, and because of the apparent behaviour of the bug, I suspect some kind of race condition here, such as a newly connected USB device that was already unconnected again before it was handled here (or unconnected just at the wrong moment). I wouldn't be surprised if such a situation caused strange, or even undefined, behaviour WRT that device, but it seems to break libusb permanently (i.e., for the lifetime of the process). I traced this to the following events: Because sysfs_can_relate_devices == 0, op_get_device_list() does not call sysfs_get_device_list() anymore, but usbfs_get_device_list(), which via usbfs_scan_busdir() calls enumerate_device() with sysfs_dir == NULL which calls initialize_device() still with sysfs_dir == NULL, so priv->sysfs_dir is not set and left NULL. Since sysfs_has_descriptors == 1, the function returns early (this might already be an error at this point, I'm not sure). Afterwards, enumerate_device() calls usbi_sanitize_device(), and via op_get_device_descriptor() and sysfs_get_device_descriptor() calls __open_sysfs_attr() which does snprintf(filename, ..., priv->sysfs_dir) which thus creates an invalid path such as "/sys/bus/usb/devices/(null)/descriptors", so open() fails which ultimately causes the failure of libusb_get_device_list(). So it seems to me that the failure to handle one device causes a permanent flag (sysfs_can_relate_devices) to be changed which seems to be the root cause of the bug. I hope this description helps you to find and fix the problem. -- System Information: Debian Release: 4.0 Architecture: i386 (i686) Shell: /bin/sh linked to /bin/bash Kernel: Linux 2.6.25-2-686 Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968) gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21) I.e., Debian etch, with a kernel from etch backports, and libusb sources from lenny backports, self compiled with "debuild -us -uc" without any additional patches. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
