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Yicon reported and Liangyan debugged a live lock in handle_edge_irq()
related to interrupt migration.
If the interrupt affinity is moved to a new target CPU and the interrupt is
currently handled on the previous target CPU for edge type interrupts the
handler might get stuck on the previous target:
CPU 0 (previous target) CPU 1 (new target)
handle_edge_irq()
repeat:
handle_event() handle_edge_irq()
if (INPROGESS) {
set(PENDING);
mask();
return;
}
if (PENDING) {
clear(PENDING);
unmask();
goto repeat;
}
The migration in software never completes and CPU0 continues to handle the
pending events forever. This happens when the device raises interrupts with
a high rate and always before handle_event() completes and before the CPU0
handler can clear INPROGRESS so that CPU1 sets the PENDING flag over and
over. This has been observed in virtual machines.
Prevent this by checking whether the CPU which observes the INPROGRESS flag
is the new affinity target. If that's the case, do not set the PENDING flag
and wait for the INPROGRESS flag to be cleared instead, so that the new
interrupt is handled on the new target CPU and the previous CPU is released
from the action.
This is restricted to the edge type handler and only utilized on systems,
which use single CPU targets for interrupt affinity.
Reported-by: Yicong Shen <shenyicong.1023@bytedance.com>
Reported-by: Liangyan <liangyan.peng@bytedance.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Liangyan <liangyan.peng@bytedance.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/all/20250701163558.2588435-1-liangyan.peng@bytedance.com
Link: https://lore.kernel.org/all/20250718185312.076515034@linutronix.de
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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.