5ac39263d8
Consider the following scenario: 1. CHN currently has its trigger set to PCMTRIG_STOP. 2. Thread A locks CHN, calls CHANNEL_TRIGGER(PCMTRIG_START), sets the trigger to PCMTRIG_START and unlocks. 3. Thread B picks up the lock, calls CHANNEL_TRIGGER(PCMTRIG_ABORT) and returns a non-zero value, so it returns from chn_trigger() as well. 4. Thread A picks up the lock and adds CHN to the list, which is _wrong_, because the last call to CHANNEL_TRIGGER() was with PCMTRIG_ABORT, meaning the channel is stopped, yet we are adding it to the list and marking it as started. Another problematic scenario: 1. Thread A locks CHN, sets the trigger to PCMTRIG_ABORT, and unlocks CHN. It then locks PCM and _removes_ CHN from the list. 2. In the meantime, since thread A unlocked CHN, thread B has locked it, set the trigger to PCMTRIG_START, unlocked it, and is now blocking on PCM held by thread A. 3. At the same time, thread C locks CHN, sets the trigger back to PCMTRIG_ABORT, unlocks CHN, and is also blocking on PCM. However, once thread A unlocks PCM, because thread C is higher-priority than thread B, it picks up the PCM lock instead of thread B, and because CHN is already removed from the list, and thread B hasn't added it back yet, we take a page fault in CHN_REMOVE() by trying to remove a non-existent element. To fix the former scenario, set the channel trigger before the call to CHANNEL_TRIGGER() (could also come after, doesn't really matter) and check if anything changed one we lock CHN back. To fix the latter scenario, use the SAFE variants of CHN_INSERT_HEAD() and CHN_REMOVE(). A similar scenario can occur in vchan_trigger(), so do the trigger setting after we've locked the parent channel. Sponsored by: The FreeBSD Foundation MFC after: 2 days Reviewed by: dev_submerge.ch Differential Revision: https://reviews.freebsd.org/D47461 |
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|---|---|---|
| .cirrus-ci | ||
| .github | ||
| bin | ||
| cddl | ||
| contrib | ||
| crypto | ||
| etc | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| stand | ||
| sys | ||
| targets | ||
| tests | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| .arcconfig | ||
| .arclint | ||
| .cirrus.yml | ||
| .clang-format | ||
| .git-blame-ignore-revs | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| CONTRIBUTING.md | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| Makefile.libcompat | ||
| Makefile.sys.inc | ||
| ObsoleteFiles.inc | ||
| README.md | ||
| RELNOTES | ||
| UPDATING | ||
FreeBSD Source:
This is the top level of the FreeBSD source directory.
FreeBSD is an operating system used to power modern servers, desktops, and embedded platforms. A large community has continually developed it for more than thirty years. Its advanced networking, security, and storage features have made FreeBSD the platform of choice for many of the busiest web sites and most pervasive embedded networking and storage devices.
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. See build(7), config(8), FreeBSD handbook on building userland, and Handbook for kernels for more information, including setting make(1) variables.
For information on the CPU architectures and platforms supported by FreeBSD, see the FreeBSD website's Platforms page.
For official FreeBSD bootable images, see the release page.
Source Roadmap:
| Directory | Description |
|---|---|
| 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. |
| gnu | Commands and libraries under the GNU General Public License (GPL) or Lesser General Public License (LGPL). Please see gnu/COPYING and gnu/COPYING.LIB 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. |
| stand | Boot loader sources. |
| sys | Kernel sources (see sys/README.md). |
| targets | Support for experimental DIRDEPS_BUILD |
| tests | Regression tests which can be run by Kyua. See tests/README for additional information. |
| 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 FreeBSD Handbook.