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simultaneously detaching kernel drivers on the same USB device we can get stuck in the "usb_wait_pending_ref_locked()" function because the conditions needed for allowing detach are not met. The "destroy_dev()" function waits for all system calls involving the given character device to return. Character device system calls may lock the USB enumeration lock, which is also held when "destroy_dev()" is called. This can sometimes lead to a deadlock not noticed by WITNESS. The current solution is to ensure the calling thread is the only one holding the USB enumeration lock and prevent other threads from getting refs while a USB device detach is ongoing. This turned out not to be sufficient. To solve this deadlock we could use "destroy_dev_sched()" to schedule the device destruction in the background, but then we don't know when it is safe to free() the private data of the character device. Instead a callback function is executed by the USB explore process to kill off any leftover USB character devices synchronously after the USB device explore code is finished and the USB enumeration lock is no longer locked. This makes porting easier and also ensures us that character devices must eventually go away after a USB device detach. While at it ensure that "flag_iserror" is only written when "priv_mtx" is locked, which is protecting it. MFC after: 5 days
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``world'' target should only be used in cases where the source tree has not changed from the currently running version. See: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html for more information, including setting make(1) variables. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you might need to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/<arch>/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/user commands. cddl Various commands and libraries under the Common Development and Distribution License. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc. games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberos5 Kerberos5 (Heimdal) package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. rescue Build system for statically linked /rescue utilities. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html