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There is quite a bit of tribal knowledge around proper use of try_module_get() and requiring *somehow* the module to still exist to use this call in a way that is safe. Document this bit of tribal knowledge. To be clear, you should only use try_module_get() *iff* you are 100% sure the module already does exist and is not on its way out. You can be sure the module still exists and is alive through: 1) Direct protection with its refcount: you know some earlier caller called __module_get() safely 2) Implied protection: there is an implied protection against module removal Having an idea of when you are sure __module_get() might be called earlier is easy to understand however the implied protection requires an example. We use sysfs an an example for implied protection without a direct module reference count bump. kernfs / sysfs uses its own internal reference counting for files being actively used, when such file are active they completely prevent the module from being removed. kernfs protects this with its kernfs_active(). Effort has been put into verifying the kernfs implied protection works by using a currently out-of-tree test_sysfs selftest test #32 [0]: ./tools/testing/selftests/sysfs/sysfs.sh -t 0032 Without kernfs / sysfs preventing module removal through its active reference count (kernfs_active()) the write would fail or worse, a crash would happen in this test and it does not. Similar safeguards are required for other users of try_module_get() *iff* they are not ensuring the above rule 1) is followed. [0] https://lore.kernel.org/lkml/20211029184500.2821444-4-mcgrof@kernel.org/ Signed-off-by: Luis Chamberlain <mcgrof@kernel.org> |
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| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| 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.