mainlining shenanigans
723aca2085
sg_miter_stop() checks for disabled preemption before unmapping a page via kunmap_atomic(). The kernel doc mentions under context that preemption must be disabled if SG_MITER_ATOMIC is set. There is no active requirement for the caller to have preemption disabled before invoking sg_mitter_stop(). The sg_mitter_*() implementation itself has no such requirement. In fact, preemption is disabled by kmap_atomic() as part of sg_miter_next() and remains disabled as long as there is an active SG_MITER_ATOMIC mapping. This is a consequence of kmap_atomic() and not a requirement for sg_mitter_*() itself. The user chooses SG_MITER_ATOMIC because it uses the API in a context where blocking is not possible or blocking is possible but he chooses a lower weight mapping which is not available on all CPUs and so it might need less overhead to setup at a price that now preemption will be disabled. The kmap_atomic() implementation on PREEMPT_RT does not disable preemption. It simply disables CPU migration to ensure that the task remains on the same CPU while the caller remains preemptible. This in turn triggers the warning in sg_miter_stop() because preemption is allowed. The PREEMPT_RT and !PREEMPT_RT implementation of kmap_atomic() disable pagefaults as a requirement. It is sufficient to check for this instead of disabled preemption. Check for disabled pagefault handler in the SG_MITER_ATOMIC case. Remove the "preemption disabled" part from the kernel doc as the sg_milter*() implementation does not care. [bigeasy@linutronix.de: commit description] Link: https://lkml.kernel.org/r/20211015211409.cqopacv3pxdwn2ty@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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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.