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fdfa588124
When testing hard lockup handling on my sc7180-trogdor-lazor device with pseudo-NMI enabled, with serial console enabled and with kgdb disabled, I found that the stack crawls printed to the serial console ended up as a jumbled mess. After rebooting, the pstore-based console looked fine though. Also, enabling kgdb to trap the panic made the console look fine and avoided the mess. After a bit of tracking down, I came to the conclusion that this was what was happening: 1. The panic path was stopping all other CPUs with panic_other_cpus_shutdown(). 2. At least one of those other CPUs was in the middle of printing to the serial console and holding the console port's lock, which is grabbed with "irqsave". ...but since we were stopping with an NMI we didn't care about the "irqsave" and interrupted anyway. 3. Since we stopped the CPU while it was holding the lock it would never release it. 4. All future calls to output to the console would end up failing to get the lock in qcom_geni_serial_console_write(). This isn't _totally_ unexpected at panic time but it's a code path that's not well tested, hard to get right, and apparently doesn't work terribly well on the Qualcomm geni serial driver. The Qualcomm geni serial driver was fixed to be a bit better in commit |
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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.