a0ec558af0
socket file descriptor garbage collection code, which is intended to detect and clear cycles of orphaned file descriptors that are "in-flight" in a socket when that socket is closed before they are received. The algorithm present was both run at poor times (resulting in recursion and reentrance), and also buggy in the presence of parallelism. In order to fix these problems, make the following changes: - When there are in-flight sockets and a UNIX domain socket is destroyed, asynchronously schedule the garbage collector, rather than running it synchronously in the current context. This avoids lock order issues when the garbage collection code reenters the UNIX domain socket code, avoiding lock order reversals, deadlocks, etc. Run the code asynchronously in a task queue. - In the garbage collector, when skipping file descriptors that have entered a closing state (i.e., have f_count == 0), re-test the FDEFER flag, and decrement unp_defer. As file descriptors can now transition to a closed state, while the garbage collector is running, it is no longer the case that unp_defer will remain an accurate count of deferred sockets in the mark portion of the GC algorithm. Otherwise, the garbage collector will loop waiting waiting for unp_defer to reach zero, which it will never do as it is skipping file descriptors that were marked in an earlier pass, but now closed. - Acquire the UNIX domain socket subsystem lock in unp_discard() when modifying the unp_rights counter, or a read/write race is risked with other threads also manipulating the counter. While here: - Remove #if 0'd code regarding acquiring the socket buffer sleep lock in the garbage collector, this is not required as we are able to use the socket buffer receive lock to protect scanning the receive buffer for in-flight file descriptors on the socket buffer. - Annotate that the description of the garbage collector implementation is increasingly inaccurate and needs to be updated. - Add counters of the number of deferred garbage collections and recycled file descriptors. This will be removed and is here temporarily for debugging purposes. With these changes in place, the unp_passfd regression test now appears to be passed consistently on UP and SMP systems for extended runs, whereas before it hung quickly or panicked, depending on which bug was triggered. Reported by: Philip Kizer <pckizer at nostrum dot com> MFC after: 2 weeks
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 ``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. 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. 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