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Petr Mladek d5d8d3d0d4 kdb: properly synchronize vkdb_printf() calls with other CPUs 
kdb_printf_lock does not prevent other CPUs from entering the critical
section because it is ignored when KDB_STATE_PRINTF_LOCK is set.

The problematic situation might look like:

CPU0					CPU1

vkdb_printf()
  if (!KDB_STATE(PRINTF_LOCK))
    KDB_STATE_SET(PRINTF_LOCK);
    spin_lock_irqsave(&kdb_printf_lock, flags);

					vkdb_printf()
					  if (!KDB_STATE(PRINTF_LOCK))

BANG: The PRINTF_LOCK state is set and CPU1 is entering the critical
section without spinning on the lock.

The problem is that the code tries to implement locking using two state
variables that are not handled atomically.  Well, we need a custom
locking because we want to allow reentering the critical section on the
very same CPU.

Let's use solution from Petr Zijlstra that was proposed for a similar
scenario, see
https://lkml.kernel.org/r/20161018171513.734367391@infradead.org

This patch uses the same trick with cmpxchg().  The only difference is
that we want to handle only recursion from the same context and
therefore we disable interrupts.

In addition, KDB_STATE_PRINTF_LOCK is removed.  In fact, we are not able
to set it a non-racy way.

Link: http://lkml.kernel.org/r/1480412276-16690-3-git-send-email-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-12-14 16:04:08 -08:00
..
bpf bpf: xdp: Allow head adjustment in XDP prog 2016-12-08 14:25:13 -05:00
configs config: android: enable CONFIG_SECCOMP 2016-10-11 15:06:32 -07:00
debug kdb: properly synchronize vkdb_printf() calls with other CPUs 2016-12-14 16:04:08 -08:00
events Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-12-10 16:21:55 -05:00
gcov gcov: add support for gcc version >= 6 2016-07-15 14:54:27 +09:00
irq Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 20:23:11 -08:00
livepatch livepatch/module: make TAINT_LIVEPATCH module-specific 2016-08-26 14:42:08 +02:00
locking Merge branch 'linus' into locking/core, to pick up fixes 2016-12-11 13:07:13 +01:00
power Merge branch 'for-4.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2016-12-13 12:59:57 -08:00
printk Merge branch 'akpm' (patches from Andrew) 2016-12-12 20:50:02 -08:00
rcu rcu: Don't kick unless grace period or request 2016-11-14 10:46:31 -08:00
sched Power management material for v4.10-rc1 2016-12-13 10:41:53 -08:00
time Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 19:56:15 -08:00
trace Merge branch 'for-4.10/block' of git://git.kernel.dk/linux-block 2016-12-13 10:19:16 -08:00
.gitignore
acct.c
async.c
audit_fsnotify.c
audit_tree.c audit: cleanup prune_tree_thread 2016-04-04 09:46:47 -04:00
audit_watch.c Merge branch 'stable-4.8' of git://git.infradead.org/users/pcmoore/audit 2016-09-01 15:55:56 -07:00
audit.c audit: remove useless synchronize_net() 2016-12-01 11:29:02 -05:00
audit.h Merge branch 'stable-4.8' of git://git.infradead.org/users/pcmoore/audit 2016-07-29 17:54:17 -07:00
auditfilter.c audit: add fields to exclude filter by reusing user filter 2016-06-27 11:01:00 -04:00
auditsc.c Merge branch 'stable-4.9' of git://git.infradead.org/users/pcmoore/audit 2016-10-04 14:21:41 -07:00
backtracetest.c
bounds.c
capability.c kernel: Add noaudit variant of ns_capable() 2016-06-06 20:16:18 +10:00
cgroup_freezer.c
cgroup_pids.c cgroup: Use lld instead of ld when printing pids controller events_limit 2016-06-21 15:03:36 -04:00
cgroup.c cgroup: add support for eBPF programs 2016-11-25 16:25:52 -05:00
compat.c posix-timers: Make them configurable 2016-11-16 09:26:35 +01:00
configs.c
context_tracking.c
cpu_pm.c
cpu.c hotplug: Make register and unregister notifier API symmetric 2016-12-08 10:08:41 +01:00
cpuset.c Merge branch 'for-4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2016-10-14 12:18:50 -07:00
crash_dump.c
cred.c cred: Reject inodes with invalid ids in set_create_file_as() 2016-06-30 18:05:09 -05:00
delayacct.c
dma.c
elfcore.c
exec_domain.c
exit.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 19:56:15 -08:00
extable.c
fork.c Power management material for v4.10-rc1 2016-12-13 10:41:53 -08:00
freezer.c freezer, oom: check TIF_MEMDIE on the correct task 2016-07-28 16:07:41 -07:00
futex_compat.c
futex.c sched/wake_q: Rename WAKE_Q to DEFINE_WAKE_Q 2016-11-21 10:29:01 +01:00
groups.c cred: simpler, 1D supplementary groups 2016-10-07 18:46:30 -07:00
hung_task.c hung_task: decrement sysctl_hung_task_warnings only if it is positive 2016-12-12 18:55:09 -08:00
irq_work.c
jump_label.c powerpc updates for 4.8 #2 2016-08-05 09:00:54 -04:00
kallsyms.c
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks locking/mutex: Allow MUTEX_SPIN_ON_OWNER when DEBUG_MUTEXES 2016-10-25 11:31:51 +02:00
Kconfig.preempt
kcov.c kcov: add more missing includes 2016-12-14 16:04:08 -08:00
kexec_core.c kexec: add cond_resched into kimage_alloc_crash_control_pages 2016-12-14 16:04:07 -08:00
kexec_file.c kexec: fix double-free when failing to relocate the purgatory 2016-09-01 17:52:01 -07:00
kexec_internal.h
kexec.c kexec: allow architectures to override boot mapping 2016-08-02 19:35:27 -04:00
kmod.c
kprobes.c kprobes: include <asm/sections.h> instead of <asm-generic/sections.h> 2016-10-11 15:06:31 -07:00
ksysfs.c kexec: add a kexec_crash_loaded() function 2016-08-02 19:35:30 -04:00
kthread.c kthread: add __printf attributes 2016-12-12 18:55:06 -08:00
latencytop.c
Makefile userns: Add per user namespace sysctls. 2016-08-08 13:18:58 -05:00
membarrier.c
memremap.c mm: fix cache mode of dax pmd mappings 2016-09-09 17:34:46 -07:00
module_signing.c KEYS: Move the point of trust determination to __key_link() 2016-04-11 22:43:43 +01:00
module-internal.h
module.c Re-enable CONFIG_MODVERSIONS in a slightly weaker form 2016-11-29 16:01:30 -08:00
notifier.c
nsproxy.c
padata.c padata: Convert to hotplug state machine 2016-09-19 21:44:30 +02:00
panic.c x86/panic: replace smp_send_stop() with kdump friendly version in panic path 2016-10-11 15:06:32 -07:00
params.c
pid_namespace.c Merge branch 'nsfs-ioctls' into HEAD 2016-09-22 20:00:36 -05:00
pid.c remove lots of IS_ERR_VALUE abuses 2016-05-27 15:26:11 -07:00
profile.c profile: Convert to hotplug state machine 2016-07-15 10:41:42 +02:00
ptrace.c mm: replace access_process_vm() write parameter with gup_flags 2016-10-19 08:31:25 -07:00
range.c
reboot.c
relay.c relay: check array offset before using it 2016-12-14 16:04:08 -08:00
resource.c /proc/iomem: only expose physical resource addresses to privileged users 2016-04-14 12:56:09 -07:00
seccomp.c bpf: drop unnecessary context cast from BPF_PROG_RUN 2016-11-27 20:38:47 -05:00
signal.c signals: avoid unnecessary taking of sighand->siglock 2016-12-14 16:04:07 -08:00
smp.c kernel/smp: Tell the user we're bringing up secondary CPUs 2016-10-26 12:02:35 +02:00
smpboot.c kthread/smpboot: do not park in kthread_create_on_cpu() 2016-10-11 15:06:33 -07:00
smpboot.h
softirq.c softirq: Display IRQ_POLL for irq-poll statistics 2016-10-21 15:45:47 -06:00
stacktrace.c
stop_machine.c locking/core, stop_machine: Yield the CPU during stop machine() 2016-11-16 10:15:09 +01:00
sys_ni.c x86/pkeys: Fix pkeys build breakage for some non-x86 arches 2016-09-13 14:41:36 +02:00
sys.c Merge branch 'akpm' (patches from Andrew) 2016-12-12 20:50:02 -08:00
sysctl_binary.c sysctl: add KERN_CONT to deprecated_sysctl_warning() 2016-12-14 16:04:07 -08:00
sysctl.c coredump: clarify "unsafe core_pattern" warning 2016-12-14 16:04:07 -08:00
task_work.c task_work: use READ_ONCE/lockless_dereference, avoid pi_lock if !task_works 2016-08-02 19:35:02 -04:00
taskstats.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-11-15 10:54:36 -05:00
test_kprobes.c
torture.c torture: Convert torture_shutdown() to hrtimer 2016-08-22 10:01:49 -07:00
tracepoint.c
tsacct.c
ucount.c mntns: Add a limit on the number of mount namespaces. 2016-08-31 07:28:35 -05:00
uid16.c cred: simpler, 1D supplementary groups 2016-10-07 18:46:30 -07:00
up.c smp: Add function to execute a function synchronously on a CPU 2016-09-05 13:52:39 +02:00
user_namespace.c Merge branch 'nsfs-ioctls' into HEAD 2016-09-22 20:00:36 -05:00
user-return-notifier.c
user.c
utsname_sysctl.c
utsname.c Merge branch 'nsfs-ioctls' into HEAD 2016-09-22 20:00:36 -05:00
watchdog.c kernel/watchdog: use nmi registers snapshot in hardlockup handler 2016-12-14 16:04:07 -08:00
workqueue_internal.h
workqueue.c Merge branch 'for-4.9' into for-4.10 2016-10-19 12:12:40 -04:00