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remarkable-linux/kernel
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John Stultz 6d9bcb621b timekeeping: use printk_deferred when holding timekeeping seqlock 
Jiri Bohac pointed out that there are rare but potential deadlock
possibilities when calling printk while holding the timekeeping
seqlock.

This is due to printk() triggering console sem wakeup, which can
cause scheduling code to trigger hrtimers which may try to read
the time.

Specifically, as Jiri pointed out, that path is:
  printk
    vprintk_emit
      console_unlock
        up(&console_sem)
          __up
	    wake_up_process
	      try_to_wake_up
	        ttwu_do_activate
		  ttwu_activate
		    activate_task
		      enqueue_task
		        enqueue_task_fair
			  hrtick_update
			    hrtick_start_fair
			      hrtick_start_fair
			        get_time
				  ktime_get
				    --> endless loop on
				    read_seqcount_retry(&timekeeper_seq, ...)

This patch tries to avoid this issue by using printk_deferred (previously
named printk_sched) which should defer printing via a irq_work_queue.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Reported-by: Jiri Bohac <jbohac@suse.cz>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-04 16:54:17 -07:00
..
debug arch: Mass conversion of smp_mb__*() 2014-04-18 14:20:48 +02:00
events Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 13:18:00 -07:00
gcov
irq genirq: x86: Ensure that dynamic irq allocation does not conflict 2014-04-28 12:20:00 +02:00
locking Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 14:00:15 -07:00
power Merge branches 'pnp', 'powercap', 'pm-runtime' and 'pm-opp' 2014-06-03 23:13:00 +02:00
printk printk: rename printk_sched to printk_deferred 2014-06-04 16:54:17 -07:00
rcu Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 12:57:53 -07:00
sched printk: Add printk_deferred_once 2014-06-04 16:54:17 -07:00
time timekeeping: use printk_deferred when holding timekeeping seqlock 2014-06-04 16:54:17 -07:00
trace tracing: Use rcu_dereference_sched() for trace event triggers 2014-05-02 23:12:42 -04:00
.gitignore
acct.c
async.c
audit.c net: Use netlink_ns_capable to verify the permisions of netlink messages 2014-04-24 13:44:54 -04:00
audit.h audit: Use struct net not pid_t to remember the network namespce to reply in 2014-03-20 10:10:53 -04:00
audit_tree.c inotify: Fix reporting of cookies for inotify events 2014-02-18 11:17:17 +01:00
audit_watch.c inotify: Fix reporting of cookies for inotify events 2014-02-18 11:17:17 +01:00
auditfilter.c Merge git://git.infradead.org/users/eparis/audit 2014-04-12 12:38:53 -07:00
auditsc.c Merge git://git.infradead.org/users/eparis/audit 2014-04-12 12:38:53 -07:00
backtracetest.c kernel/backtracetest.c: replace no level printk by pr_info() 2014-06-04 16:54:14 -07:00
bounds.c
capability.c kernel/capability.c: code clean-up 2014-06-04 16:54:15 -07:00
cgroup.c kernfs: move the last knowledge of sysfs out from kernfs 2014-05-27 14:33:17 -07:00
cgroup_freezer.c cgroup: fix rcu_read_lock() leak in update_if_frozen() 2014-05-13 11:28:30 -04:00
compat.c Merge branch 'x86-x32-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-04-02 12:51:41 -07:00
configs.c
context_tracking.c asmlinkage: Add explicit __visible to drivers/*, lib/*, kernel/* 2014-05-05 16:07:46 -07:00
cpu.c kernel/cpu.c: convert printk to pr_foo() 2014-06-04 16:54:14 -07:00
cpu_pm.c
cpuset.c mm: page_alloc: use jump labels to avoid checking number_of_cpusets 2014-06-04 16:54:08 -07:00
crash_dump.c
cred.c
delayacct.c
dma.c
elfcore.c
exec_domain.c kernel/exec_domain.c: code clean-up 2014-06-04 16:54:15 -07:00
exit.c memcg: optimize the "Search everything else" loop in mm_update_next_owner() 2014-06-04 16:54:03 -07:00
extable.c asmlinkage: Make main_extable_sort_needed visible 2014-02-13 18:13:22 -08:00
fork.c memcg: kill CONFIG_MM_OWNER 2014-06-04 16:54:01 -07:00
freezer.c
futex.c Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 12:57:53 -07:00
futex_compat.c compat: Get rid of (get|put)_compat_time(val|spec) 2014-02-02 14:09:12 -08:00
groups.c kernel/groups.c: remove return value of set_groups 2014-04-03 16:21:05 -07:00
hrtimer.c Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 13:18:00 -07:00
hung_task.c kernel/hung_task.c: convert simple_strtoul to kstrtouint 2014-06-04 16:54:15 -07:00
irq_work.c perf/x86: Warn to early_printk() in case irq_work is too slow 2014-02-21 21:49:07 +01:00
itimer.c
jump_label.c
kallsyms.c kernel: use macros from compiler.h instead of __attribute__((...)) 2014-04-07 16:36:11 -07:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kexec.c powerpc, kexec: Fix "Processor X is stuck" issue during kexec from ST mode 2014-05-28 13:24:26 +10:00
kmod.c arch: Mass conversion of smp_mb__*() 2014-04-18 14:20:48 +02:00
kprobes.c
ksysfs.c kobject: Make support for uevent_helper optional. 2014-04-25 12:00:49 -07:00
kthread.c kthread: fix return value of kthread_create() upon SIGKILL. 2014-06-04 16:53:51 -07:00
latencytop.c kernel/latencytop.c: convert seq_printf to seq_puts 2014-06-04 16:54:15 -07:00
Makefile Merge branch 'x86-asmlinkage-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-03-31 14:13:25 -07:00
module-internal.h
module.c Fixed one missing place for the new taint flag, and remove a warning 2014-05-01 10:35:01 -07:00
module_signing.c
notifier.c notifier: Substitute rcu_access_pointer() for rcu_dereference_raw() 2014-02-26 06:35:13 -08:00
nsproxy.c
padata.c
panic.c kernel/panic.c: display reason at end + pr_emerg 2014-04-07 16:36:08 -07:00
params.c
pid.c
pid_namespace.c pid_namespace: pidns_get() should check task_active_pid_ns() != NULL 2014-04-02 16:20:21 -07:00
posix-cpu-timers.c
posix-timers.c
profile.c CPU hotplug notifiers registration fixes for 3.15-rc1 2014-04-07 14:55:46 -07:00
ptrace.c kernel/compat: convert to COMPAT_SYSCALL_DEFINE 2014-03-06 15:35:10 +01:00
range.c
reboot.c kernel/reboot.c: convert simple_strtoul to kstrtoint 2014-06-04 16:54:15 -07:00
relay.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2014-04-12 14:49:50 -07:00
res_counter.c kernel/res_counter.c: replace simple_strtoull by kstrtoull 2014-06-04 16:54:15 -07:00
resource.c resources: Clarify sanity check message 2014-05-23 10:47:21 -06:00
seccomp.c seccomp: fix memory leak on filter attach 2014-04-16 15:25:53 -04:00
signal.c sys_sgetmask/sys_ssetmask: add CONFIG_SGETMASK_SYSCALL 2014-06-04 16:54:14 -07:00
smp.c smp: Rename __smp_call_function_single() to smp_call_function_single_async() 2014-02-24 14:47:15 -08:00
smpboot.c
smpboot.h
softirq.c Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu 2014-05-22 11:36:10 +02:00
stacktrace.c
stop_machine.c kernel/stop_machine.c: kernel-doc warning fix 2014-06-04 16:54:15 -07:00
sys.c sched: Consolidate open coded implementations of nice level frobbing into nice_to_rlimit() and rlimit_to_nice() 2014-05-22 11:16:36 +02:00
sys_ni.c sys_sgetmask/sys_ssetmask: add CONFIG_SGETMASK_SYSCALL 2014-06-04 16:54:14 -07:00
sysctl.c kobject: Make support for uevent_helper optional. 2014-04-25 12:00:49 -07:00
sysctl_binary.c
system_certificates.S
system_keyring.c
task_work.c
taskstats.c
test_kprobes.c
time.c
timeconst.bc
timer.c timer: Prevent overflow in apply_slack 2014-04-30 13:46:17 +02:00
torture.c torture: Remove __init from torture_init_begin/end 2014-05-14 09:46:30 -07:00
tracepoint.c kernel/tracepoint.c: kernel-doc fixes 2014-06-04 16:54:15 -07:00
tsacct.c
uid16.c
up.c smp: Rename __smp_call_function_single() to smp_call_function_single_async() 2014-02-24 14:47:15 -08:00
user-return-notifier.c
user.c kernel/user.c: drop unused field 'files' from user_struct 2014-06-04 16:54:16 -07:00
user_namespace.c user namespace: fix incorrect memory barriers 2014-04-14 16:03:02 -07:00
utsname.c
utsname_sysctl.c kernel/utsname_sysctl.c: replace obsolete __initcall by device_initcall 2014-06-04 16:54:15 -07:00
watchdog.c kernel/watchdog.c:touch_softlockup_watchdog(): use raw_cpu_write() 2014-04-18 16:40:08 -07:00
workqueue.c Linux 3.15-rc6 2014-05-22 10:28:56 +02:00
workqueue_internal.h