Hans Petter Selasky 0eb8d46232 Improve USB polling mode by not locking any mutexes, asserting any
mutexes or using any callouts when active.

Trying to lock a mutex when KDB is active or the scheduler is stopped
can result in infinite wait loops. The same goes for calling callout
related functions which in turn lock mutexes.

If the USB controller at which a USB keyboard is connected is idle
when KDB is entered, polling the USB keyboard via USB will always
succeed. Else polling may fail depending on which state the USB
subsystem and USB interrupt handler is in. This is unavoidable unless
KDB can wait for USB interrupt threads to complete before stalling the
CPU(s).

Tested by:	Bruce Evans <bde@freebsd.org>
MFC after:	4 weeks
2016-09-14 12:07:34 +00:00
2016-09-03 00:50:18 +00:00
2016-09-09 01:09:39 +00:00
2016-09-11 18:56:38 +00:00
2016-09-11 18:56:38 +00:00
2015-04-20 20:33:22 +00:00
2015-12-31 11:21:45 +00:00
2016-09-08 23:49:33 +00:00
2016-09-11 19:51:32 +00:00

This is the top level of the FreeBSD source directory.  This file
was last revised on:
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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
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The Makefile in this directory supports a number of targets for
building components (or all) of the FreeBSD source tree.  See build(7)
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for more information, including setting make(1) variables.

The `buildkernel` and `installkernel` targets build and install
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the Makefile in this directory for more information on the
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Building a kernel is a somewhat more involved process.  See build(7), config(8),
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Note: If you want to build and install the kernel with the
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The kernel configuration files reside in the sys/<arch>/conf
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NOTES contains entries and documentation for all possible
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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.
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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.

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.


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  http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html
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