freebsd kernel with SKQ
24dd1a8242
At present zfs_domount() acquires a reference on the filesystem's root vnode and that reference is kept until zfs_umount. The latter calls vflush(rootrefs = 1) to dispose of the extra reference. There is no explanation of why that reference is kept - what problem it solves or what behavior it improves. Also, that logic is FreeBSD specific. There is one real problem with that reference, though. zfs recv -F may receive a full, non-incremental stream to a mounted filesystem. In that case the received root object is likely to have a different z_gen attribute value. Because of that, zfs_rezget will leave the previous root znode and vnode disassociated from the actual object (z_sa_hdl == NULL). Thus, future calls to VFS_ROOT() -> zfs_root() will produce a new vnode-znode pair, while the old one will be kept alive by the outstanding reference. So, the outstanding reference will not actually be for the new root vnode (or, more precisely, vnodes - because a root vnode may be recycled and a newer one can be created). As a result, when vflush(rootrefs = 1) s called there will be two problems: - a leaked reference on the old root vnode preventing a graceful unmount - insufficient references on the actual root vnode leading to a crash upon access to the vnode after it is destroyed by vgone() + vdrop() The second issue will actually override the first one. Differential Revision: https://reviews.freebsd.org/D2353 Reviewed by: delphij, kib, smh MFC after: 17 days |
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| 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. See build(7) and 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. See build(7), config(8), and http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html for more information. 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 kernel configuration files reside in the sys/<arch>/conf sub-directory. GENERIC is the default configuration used in release builds. NOTES contains entries and documentation for all possible devices, not just those commonly used. 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. 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: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html