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The arm64 entry code only preempts a kernel context upon a return from
a regular IRQ exception. The generic entry code may preempt a kernel
context for any exception return where irqentry_exit() is used, and so
may preempt other exceptions such as faults.
In preparation for moving arm64 over to the generic entry code, align
arm64 with the generic behaviour by calling
arm64_preempt_schedule_irq() from exit_to_kernel_mode(). To make this
possible, arm64_preempt_schedule_irq()
and dynamic/raw_irqentry_exit_cond_resched() are moved earlier in
the file, with no changes.
As Mark pointed out, this change will have the following 2 key impact:
- " We'll preempt even without taking a "real" interrupt. That
shouldn't result in preemption that wasn't possible before,
but it does change the probability of preempting at certain points,
and might have a performance impact, so probably warrants a
benchmark."
- " We will not preempt when taking interrupts from a region of kernel
code where IRQs are enabled but RCU is not watching, matching the
behaviour of the generic entry code.
This has the potential to introduce livelock if we can ever have a
screaming interrupt in such a region, so we'll need to go figure out
whether that's actually a problem.
Having this as a separate patch will make it easier to test/bisect
for that specifically."
Reviewed-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
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 reStructuredText 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.