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Valentin Schneider 0cf2833400 panic, kexec: make __crash_kexec() NMI safe 
commit 05c6257433 upstream.

Attempting to get a crash dump out of a debug PREEMPT_RT kernel via an NMI
panic() doesn't work.  The cause of that lies in the PREEMPT_RT definition
of mutex_trylock():

	if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES) && WARN_ON_ONCE(!in_task()))
		return 0;

This prevents an nmi_panic() from executing the main body of
__crash_kexec() which does the actual kexec into the kdump kernel.  The
warning and return are explained by:

  6ce47fd961 ("rtmutex: Warn if trylock is called from hard/softirq context")
  [...]
  The reasons for this are:

      1) There is a potential deadlock in the slowpath

      2) Another cpu which blocks on the rtmutex will boost the task
	 which allegedly locked the rtmutex, but that cannot work
	 because the hard/softirq context borrows the task context.

Furthermore, grabbing the lock isn't NMI safe, so do away with kexec_mutex
and replace it with an atomic variable.  This is somewhat overzealous as
*some* callsites could keep using a mutex (e.g.  the sysfs-facing ones
like crash_shrink_memory()), but this has the benefit of involving a
single unified lock and preventing any future NMI-related surprises.

Tested by triggering NMI panics via:

  $ echo 1 > /proc/sys/kernel/panic_on_unrecovered_nmi
  $ echo 1 > /proc/sys/kernel/unknown_nmi_panic
  $ echo 1 > /proc/sys/kernel/panic

  $ ipmitool power diag

Link: https://lkml.kernel.org/r/20220630223258.4144112-3-vschneid@redhat.com
Fixes: 6ce47fd961 ("rtmutex: Warn if trylock is called from hard/softirq context")
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Juri Lelli <jlelli@redhat.com>
Cc: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2023-04-20 12:13:57 +02:00
Documentation tcp: restrict net.ipv4.tcp_app_win 2023-04-20 12:13:53 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
arch x86/rtc: Remove __init for runtime functions 2023-04-20 12:13:56 +02:00
block block: don't allow multiple bios for IOCB_NOWAIT issue 2023-03-10 09:39:55 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto asymmetric_keys: log on fatal failures in PE/pkcs7 2023-04-20 12:13:54 +02:00
drivers nvme-pci: add NVME_QUIRK_BOGUS_NID for T-FORCE Z330 SSD 2023-04-20 12:13:57 +02:00
fs btrfs: fix fast csum implementation detection 2023-04-20 12:13:52 +02:00
include kexec: turn all kexec_mutex acquisitions into trylocks 2023-04-20 12:13:57 +02:00
init kbuild: Add CONFIG_PAHOLE_VERSION 2023-02-25 12:06:45 +01:00
io_uring io_uring: avoid null-ptr-deref in io_arm_poll_handler 2023-03-22 13:31:37 +01:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:28:45 +01:00
kernel panic, kexec: make __crash_kexec() NMI safe 2023-04-20 12:13:57 +02:00
lib kobject: Fix slab-out-of-bounds in fill_kobj_path() 2023-03-10 09:39:35 +01:00
mm mm: take a page reference when removing device exclusive entries 2023-04-13 16:48:26 +02:00
net mptcp: stricter state check in mptcp_worker 2023-04-20 12:13:56 +02:00
samples samples: vfio-mdev: Fix missing pci_disable_device() in mdpy_fb_probe() 2022-12-31 13:14:31 +01:00
scripts kconfig: Update config changed flag before calling callback 2023-03-22 13:31:29 +01:00
security keys: Do not cache key in task struct if key is requested from kernel thread 2023-03-30 12:47:47 +02:00
sound ALSA: hda/sigmatel: fix S/PDIF out on Intel D*45* motherboards 2023-04-20 12:13:52 +02:00
tools libbpf: Fix single-line struct definition output in btf_dump 2023-04-20 12:13:54 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: fix memoryleak in kvm_init() 2023-03-17 08:49:04 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
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.get_maintainer.ignore
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.gitattributes
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.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS counter: Internalize sysfs interface code 2023-04-20 12:13:55 +02:00
Makefile Linux 5.15.107 2023-04-13 16:48:27 +02:00
README
…

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.