mainlining shenanigans
9e343b467c
{READ,WRITE}_ONCE() cannot guarantee atomicity for arbitrary data sizes.
This can be surprising to callers that might incorrectly be expecting
atomicity for accesses to aggregate structures, although there are other
callers where tearing is actually permissable (e.g. if they are using
something akin to sequence locking to protect the access).
Linus sayeth:
| We could also look at being stricter for the normal READ/WRITE_ONCE(),
| and require that they are
|
| (a) regular integer types
|
| (b) fit in an atomic word
|
| We actually did (b) for a while, until we noticed that we do it on
| loff_t's etc and relaxed the rules. But maybe we could have a
| "non-atomic" version of READ/WRITE_ONCE() that is used for the
| questionable cases?
The slight snag is that we also have to support 64-bit accesses on 32-bit
architectures, as these appear to be widespread and tend to work out ok
if either the architecture supports atomic 64-bit accesses (x86, armv7)
or if the variable being accesses represents a virtual address and
therefore only requires 32-bit atomicity in practice.
Take a step in that direction by introducing a variant of
'compiletime_assert_atomic_type()' and use it to check the pointer
argument to {READ,WRITE}_ONCE(). Expose __{READ,WRITE}_ONCE() variants
which are allowed to tear and convert the one broken caller over to the
new macros.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Will Deacon <will@kernel.org>
|
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|---|---|---|
| arch | ||
| block | ||
| 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.