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If no handler (such as rpc.mountd) has opened a cache 'channel', the sunrpc cache responds to all lookup requests with -ENOENT. This is particularly important for the auth.unix.gid cache which is optional. If the channel was open briefly and an upcall was written to it, this upcall remains pending even when the handler closes the channel. When an upcall is pending, the code currently doesn't check if there are still listeners, it only performs that check before sending an upcall. As the cache treads a recently closes channel (closed less than 30 seconds ago) as "potentially still open", there is a reasonable sized window when a request can become pending in a closed channel, and thereby block lookups indefinitely. This can easily be demonstrated by running cat /proc/net/rpc/auth.unix.gid/channel and then trying to mount an NFS filesystem from this host. It will block indefinitely (unless mountd is run with --manage-gids, or krb5 is used). When cache_check() finds that an upcall is pending, it should perform the "cache_listeners_exist()" exist test. If no listeners do exist, the request should be negated. With this change in place, there can still be a 30second wait on mount, until the cache gives up waiting for a handler to come back, but this is much better than an indefinite wait. Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com> |
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| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.