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A CPU executing with console lock spinning enabled might be halted
during a panic. Before the panicking CPU calls console_flush_on_panic(),
it may call console_trylock(), which attempts to optimistically spin,
deadlocking the panic CPU:
CPU 0 (panic CPU) CPU 1
----------------- ------
printk() {
vprintk_func() {
vprintk_default() {
vprintk_emit() {
console_unlock() {
console_lock_spinning_enable();
... printing to console ...
panic() {
crash_smp_send_stop() {
NMI -------------------> HALT
}
atomic_notifier_call_chain() {
printk() {
...
console_trylock_spinnning() {
// optimistic spin infinitely
This hang during panic can be induced when a kdump kernel is loaded, and
crash_kexec_post_notifiers=1 is present on the kernel command line. The
following script which concurrently writes to /dev/kmsg, and triggers a
panic, can result in this hang:
#!/bin/bash
date
# 991 chars (based on log buffer size):
chars="$(printf 'a%.0s' {1..991})"
while :; do
echo $chars > /dev/kmsg
done &
echo c > /proc/sysrq-trigger &
date
exit
To avoid this deadlock, ensure that console_trylock_spinning() does not
allow spinning once a panic has begun.
Fixes:
|
||
|---|---|---|
| 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.