freebsd kernel with SKQ
dfdf9abd94
promoted" panics. The sequence of events that leads to a panic is rather long and circuitous. First, suppose that process P has a promoted superpage S within vm object O that it can write to. Then, suppose that P forks, which leads to S being write protected. Now, before P's child exits, suppose that P writes to another virtual page within O. Since the pages within O are copy on write, a shadow object for O is created to house the new physical copy of the faulted on virtual page. Then, before P can fault on S, P's child exists. Now, when P faults on S, it will follow the "optimized" path for copy-on-write faults in vm_fault(), wherein the underlying physical page is moved from O to its shadow object rather than allocating a new page and copying the new page's contents from the old page. Moreover, suppose that every 4 KB physical page making up S is moved to the shadow object in this way. However, the optimized path does not move the underlying superpage reservation, which is the root cause of the panics! Ultimately, P performs vm_object_collapse() on O's shadow object, which destroys O and in doing so breaks any reservations still belonging to O. This leaves the reservation underlying S in an inconsistent state: It's simultaneously not in use and promoted. Breaking a reservation does not demote it because I never intended for a promoted reservation to be broken. It makes little sense. Finally, this inconsistency leads to an assertion failure the next time that the reservation is used. The failing assertion does not (currently) exist in FreeBSD 10.x or earlier. There, we will quietly break the promoted reservation. While illogical and unintended, breaking the reservation is essentially harmless. PR: 198163 Reviewed by: kib Tested by: pho X-MFC after: r267213 Sponsored by: EMC / Isilon Storage Division |
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| bin | ||
| cddl | ||
| contrib | ||
| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| tests | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| .arcconfig | ||
| .arclint | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| ObsoleteFiles.inc | ||
| README | ||
| UPDATING | ||
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 ``world'' target should only be used in cases where the source tree has not changed from the currently running version. See: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html for more information, including setting make(1) variables. 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. 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. 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. rescue Build system for statically linked /rescue utilities. 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