e0fa977ea5
The code that iterates a list of interrupt handlers for a (shared) interrupt, whether in the ISR context or in the context of an interrupt thread, does so in a lock-free fashion. Thus, the routines that modify the list need to take special steps to ensure that the iterating code has a consistent view of the list. Previously, those routines tried to play nice only with the code running in the ithread context. The iteration in the ISR context was left to a chance. After commit r336635 atomic operations and memory fences are used to ensure that ie_handlers list is always safe to navigate with respect to inserting and removal of list elements. There is still a question of when it is safe to actually free a removed element. The idea of this change is somewhat similar to the idea of the epoch based reclamation. There are some simplifications comparing to the general epoch based reclamation. All writers are serialized using a mutex, so we do not need to worry about concurrent modifications. Also, all read accesses from the open context are serialized too. So, we can get away just two epochs / phases. When a thread removes an element it switches the global phase from the current phase to the other and then drains the previous phase. Only after the draining the removed element gets actually freed. The code that iterates the list in the ISR context takes a snapshot of the global phase and then increments the use count of that phase before iterating the list. The use count (in the same phase) is decremented after the iteration. This should ensure that there should be no iteration over the removed element when its gets freed. This commit also simplifies the coordination with the interrupt thread context. Now we always schedule the interrupt thread when removing one of handlers for its interrupt. This makes the code both simpler and safer as the interrupt thread masks the interrupt thus ensuring that there is no interaction with the ISR context. P.S. This change matters only for shared interrupts and I realize that those are becoming a thing of the past (and quickly). I also understand that the problem that I am trying to solve is extremely rare. PR: 229106 Reviewed by: cem Discussed with: Samy Al Bahra MFC after: 5 weeks Differential Revision: https://reviews.freebsd.org/D15905
FreeBSD Source:
This is the top level of the FreeBSD source directory. This file
was last revised on:
FreeBSD
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), https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html, and https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html for more information, including setting make(1) variables.
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.
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.
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:
https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/current-stable.html