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Mark Johnston 893be9d8ac sleepqueue: Address a lock order reversal 
After commit 74cf7cae4d ("softclock: Use dedicated ithreads for
running callouts."), there is a lock order reversal between the per-CPU
callout lock and the scheduler lock.  softclock_thread() locks callout
lock then the scheduler lock, when preparing to switch off-CPU, and
sleepq_remove_thread() stops the timed sleep callout while potentially
holding a scheduler lock.  In the latter case, it's the thread itself
that's locked, and if the thread is sleeping then its lock will be a
sleepqueue lock, but if it's still in the process of going to sleep
it'll be a scheduler lock.

We could perhaps change softclock_thread() to try to acquire locks in
the opposite order, but that'd require dropping and re-acquiring the
callout lock, which seems expensive for an operation that will happen
quite frequently.  We can instead perhaps avoid stopping the
td_slpcallout callout if the thread is still going to sleep, which is
what this patch does.  This will result in a spurious call to
sleepq_timeout(), but some counters suggest that this is very rare.

PR:		261198
Fixes:		74cf7cae4d ("softclock: Use dedicated ithreads for running callouts.")
Reported and tested by:	thj
Reviewed by:	kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D34204
2022-02-14 10:06:47 -05:00
.cirrus-ci Cirrus-CI: add some timing info on pkg install failure 2021-08-04 15:02:00 -04:00
.github Update vendor/libarchive libarchive/libarchive@9147def1d 2022-02-09 14:20:23 +01:00
bin bin/df: allow -t option to be used together with -l 2022-02-10 21:09:34 +01:00
cddl ctfconvert: Rip out STABS support 2022-02-10 15:41:10 -05:00
contrib libarchive: import changes from upstream 2022-02-10 00:35:42 +01:00
crypto OpenSSL: Fix the same BIO_FLAGS macro definition 2022-02-01 10:38:49 -08:00
etc Append Keyboard Layout specified option for using VNC. 2022-01-20 23:49:27 +01:00
gnu libdialog: Bump shared library version to 10. 2021-10-27 09:30:24 -07:00
include Install unwind.h into /usr/include 2022-02-10 19:00:32 +01:00
kerberos5 pkgbase: Create a FreeBSD-kerberos package 2021-09-07 10:23:14 +02:00
lib libthr: Disable stack unwinding on ARM. 2022-02-10 12:47:08 -08:00
libexec rtld: Add ${TOKEN} aliases to $TOKEN 2022-02-11 20:01:20 +02:00
release release: Don't install ubldr.bin 2022-02-07 13:19:20 -07:00
rescue rescue: Link with -lncursesw instead of -lncursesw_real. 2022-02-11 13:58:59 -08:00
sbin dmesg: detect wrapped msgbuf on the kernel side and if so, skip first line 2022-02-05 13:35:31 -08:00
secure OpenSSL: Merge OpenSSL 1.1.1m 2021-12-14 16:03:52 -05:00
share cpuset.9: add description of CPU_ISSET() 2022-02-14 15:59:37 +01:00
stand Add support for module_verbose 2022-02-13 12:45:57 -08:00
sys sleepqueue: Address a lock order reversal 2022-02-14 10:06:47 -05:00
targets Retire obsolete iscsi_initiator(4) 2021-10-26 16:17:35 -04:00
tests [skip ci] fusefs: delete a stray comment from 91972cfcdd 2022-02-12 09:27:56 -07:00
tools stress2: Add a fsck_ffs regression test scenario 2022-02-13 10:49:58 +01:00
usr.bin Better help message if locate database does not exists 2022-02-13 17:00:22 +00:00
usr.sbin freebsd-update: improve BE creation feature 2022-02-12 15:36:24 -06:00
.arcconfig Remove history.immutable from .arcconfig 2021-04-13 12:36:25 +01:00
.arclint arc lint: ignore /tests/ in chmod 2017-12-19 03:38:06 +00:00
.cirrus.yml Cirrus-CI: build with LLVM 13 package 2021-11-18 09:57:33 -05:00
.clang-format clang-format: Add bitset loop macros 2021-09-21 12:08:01 -04:00
.gitattributes Add a basic clang-format configuration file 2019-06-07 15:23:52 +00:00
.gitignore Update vendor/libarchive libarchive/libarchive@9147def1d 2022-02-09 14:20:23 +01:00
COPYRIGHT Welcome 2022, update copyrights. 2022-01-01 09:49:49 -07:00
LOCKS LOCKS: update current locks 2018-06-09 03:08:04 +00:00
MAINTAINERS Remove myself from bhyve maintenance; ENOTIME. 2021-11-19 07:09:30 +10:00
Makefile cleankernel: A target to delete the kernel compile file 2022-02-11 12:51:24 -07:00
Makefile.inc1 cleankernel: A target to delete the kernel compile file 2022-02-11 12:51:24 -07:00
Makefile.libcompat Makefile.libcompat: Sort 2022-02-02 14:34:29 -07:00
Makefile.sys.inc AUTO_OBJ: For all top-level targets enforce using an OBJDIR. 2017-12-05 21:29:47 +00:00
ObsoleteFiles.inc Install unwind.h into /usr/include 2022-02-10 19:00:32 +01:00
README.md README.md: update gnu directory description 2021-12-17 08:45:31 -05:00
RELNOTES RELNOTES: Note support for KTLS RX for TLS 1.3. 2021-12-14 11:02:45 -08:00
UPDATING Fix minor grammar nit. 2022-01-31 15:35:23 -08:00

README.md

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.

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.
sys/arch/conf Kernel configuration files. GENERIC is the configuration used in release builds. NOTES contains documentation of all possible entries.
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.