linux/arch/powerpc
Nicholas Piggin 76521c4b02 powerpc/watchdog: Avoid holding wd_smp_lock over printk and smp_send_nmi_ipi
There is a deadlock with the console_owner lock and the wd_smp_lock:

CPU x takes the console_owner lock
CPU y takes a watchdog timer interrupt and takes __wd_smp_lock
CPU x takes a soft-NMI interrupt, detects deadlock, spins on __wd_smp_lock
CPU y detects deadlock, tries to print something and spins on console_owner
-> deadlock

Change the watchdog locking scheme so wd_smp_lock protects the watchdog
internal data, but "reporting" (printing, issuing NMI IPIs, taking any
action outside of watchdog) uses a non-waiting exclusion. If a CPU detects
a problem but can not take the reporting lock, it just returns because
something else is already reporting. It will try again at some point.

Typically hard lockup watchdog report usefulness is not impacted due to
failure to spewing a large enough amount of data in as short a time as
possible, but by messages getting garbled.

Laurent debugged this and found the deadlock, and this patch is based on
his general approach to avoid expensive operations while holding the lock.
With the addition of the reporting exclusion.

Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
[np: rework to add reporting exclusion update changelog]
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211110025056.2084347-4-npiggin@gmail.com
2021-11-25 11:25:33 +11:00
..
boot powerpc updates for 5.16 2021-11-05 08:15:46 -07:00
configs powerpc/pseries: delete scanlog 2021-11-25 11:25:33 +11:00
crypto crypto: powepc/sha1 - remove unneeded semicolon 2021-03-07 15:13:14 +11:00
include powerpc/rtas: rtas_busy_delay() improvements 2021-11-25 11:25:33 +11:00
kernel powerpc/watchdog: Avoid holding wd_smp_lock over printk and smp_send_nmi_ipi 2021-11-25 11:25:33 +11:00
kexec powerpc/machdep: Remove stale functions from ppc_md structure 2021-10-22 15:22:05 +11:00
kvm KVM: PPC: Book3S HV P9: Remove subcore HMI handling 2021-11-24 21:09:03 +11:00
lib powerpc/code-patching: Improve verification of patchability 2021-11-25 11:25:32 +11:00
math-emu powerpc/64s: avoid reloading (H)SRR registers if they are still valid 2021-06-25 00:06:55 +10:00
mm powerpc/code-patching: Improve verification of patchability 2021-11-25 11:25:32 +11:00
net bpf ppc32: Access only if addr is kernel address 2021-11-25 11:25:32 +11:00
perf powerpc/64s: Implement PMU override command line option 2021-11-24 21:08:57 +11:00
platforms powerpc/pseries: delete scanlog 2021-11-25 11:25:33 +11:00
purgatory powerpc/kexec: Don't use .machine ppc64 in trampoline_64.S 2021-04-08 21:17:43 +10:00
sysdev powerpc/tsi108: make EXPORT_SYMBOL follow its function immediately 2021-11-25 11:25:32 +11:00
tools powerpc/head_check: Fix shellcheck errors 2021-08-17 22:52:02 +10:00
xmon powerpc/64s: guard optional TIDR SPR with CPU ftr test 2021-11-24 21:08:56 +11:00
Kbuild kbuild: use more subdir- for visiting subdirectories while cleaning 2021-10-24 13:49:46 +09:00
Kconfig powerpc/64s: Default to 64K pages for 64 bit book3s 2021-10-27 22:31:22 +11:00
Kconfig.debug powerpc/ptdump: Convert powerpc to GENERIC_PTDUMP 2021-08-25 13:35:48 +10:00
Makefile Kbuild updates for v5.16 2021-11-08 09:15:45 -08:00
Makefile.postlink powerpc: unrel_branch_check.sh: use nm to find symbol value 2020-09-02 11:00:22 +10:00