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Johan Hovold 57116ce17b workqueue: fix state-dump console deadlock 
Console drivers often queue work while holding locks also taken in their
console write paths, something which can lead to deadlocks on SMP when
dumping workqueue state (e.g. sysrq-t or on suspend failures).

For serial console drivers this could look like:

	CPU0				CPU1
	----				----

	show_workqueue_state();
	  lock(&pool->lock);		<IRQ>
	  				  lock(&port->lock);
					  schedule_work();
					    lock(&pool->lock);
	  printk();
	    lock(console_owner);
	    lock(&port->lock);

where workqueues are, for example, used to push data to the line
discipline, process break signals and handle modem-status changes. Line
disciplines and serdev drivers can also queue work on write-wakeup
notifications, etc.

Reworking every console driver to avoid queuing work while holding locks
also taken in their write paths would complicate drivers and is neither
desirable or feasible.

Instead use the deferred-printk mechanism to avoid printing while
holding pool locks when dumping workqueue state.

Note that there are a few WARN_ON() assertions in the workqueue code
which could potentially also trigger a deadlock. Hopefully the ongoing
printk rework will provide a general solution for this eventually.

This was originally reported after a lockdep splat when executing
sysrq-t with the imx serial driver.

Fixes: 3494fc3084 ("workqueue: dump workqueues on sysrq-t")
Cc: stable@vger.kernel.org	# 4.0
Reported-by: Fabio Estevam <festevam@denx.de>
Tested-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Tejun Heo <tj@kernel.org>
2021-10-11 06:50:28 -10:00
..
bpf Merge https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2021-08-30 16:42:47 -07:00
cgroup Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
configs drivers/char: remove /dev/kmem for good 2021-05-07 00:26:34 -07:00
debug kgdb patches for 5.15 2021-09-07 12:08:04 -07:00
dma Merge branch 'stable/for-linus-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb 2021-09-03 10:34:44 -07:00
entry tick/nohz: Only check for RCU deferred wakeup on user/guest entry when needed 2021-05-31 10:14:49 +02:00
events Merge tag 'denywrite-for-5.15' of git://github.com/davidhildenbrand/linux 2021-09-04 11:35:47 -07:00
gcov Kconfig: Introduce ARCH_WANTS_NO_INSTR and CC_HAS_NO_PROFILE_FN_ATTR 2021-06-22 11:07:18 -07:00
irq powerpc updates for 5.15 2021-09-03 11:22:50 -07:00
kcsan LKMM updates: 2021-09-02 13:00:15 -07:00
livepatch livepatch: Replace deprecated CPU-hotplug functions. 2021-08-19 12:00:24 +02:00
locking locking/rtmutex: Fix ww_mutex deadlock check 2021-09-09 10:31:22 +02:00
power Merge branches 'pm-pci', 'pm-sleep', 'pm-domains' and 'powercap' 2021-08-30 19:25:42 +02:00
printk Merge branch 'rework/printk_safe-removal' into for-linus 2021-08-30 16:36:10 +02:00
rcu Updates for locking and atomics: 2021-08-30 14:26:36 -07:00
sched - Make sure the idle timer expires in hardirq context, on PREEMPT_RT 2021-09-12 11:37:41 -07:00
time Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
trace Minor fixes to the processing of the bootconfig tree. 2021-09-11 10:16:30 -07:00
.gitignore .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
acct.c kernel/acct.c: use dedicated helper to access rlimit values 2021-09-08 11:50:26 -07:00
async.c kernel/async.c: remove async_unregister_domain() 2021-05-07 00:26:33 -07:00
audit.c lsm: separate security_task_getsecid() into subjective and objective variants 2021-03-22 15:23:32 -04:00
audit.h audit: add header protection to kernel/audit.h 2021-07-19 22:38:24 -04:00
audit_fsnotify.c
audit_tree.c audit: move put_tree() to avoid trim_trees refcount underflow and UAF 2021-08-24 18:52:36 -04:00
audit_watch.c
auditfilter.c lsm: separate security_task_getsecid() into subjective and objective variants 2021-03-22 15:23:32 -04:00
auditsc.c audit: remove trailing spaces and tabs 2021-06-10 20:59:05 -04:00
backtracetest.c
bounds.c
capability.c
cfi.c cfi: Use rcu_read_{un}lock_sched_notrace 2021-08-11 13:11:12 -07:00
compat.c arch: remove compat_alloc_user_space 2021-09-08 15:32:35 -07:00
configs.c
context_tracking.c
cpu.c cpu/hotplug: Add debug printks for hotplug callback failures 2021-08-10 18:31:32 +02:00
cpu_pm.c PM: cpu: Make notifier chain use a raw_spinlock_t 2021-08-16 18:55:32 +02:00
crash_core.c kdump: use vmlinux_build_id to simplify 2021-07-08 11:48:22 -07:00
crash_dump.c
cred.c ucounts: Increase ucounts reference counter before the security hook 2021-08-23 16:13:04 -05:00
delayacct.c delayacct: Add sysctl to enable at runtime 2021-05-12 11:43:25 +02:00
dma.c
exec_domain.c
exit.c io_uring: remove files pointer in cancellation functions 2021-08-23 13:10:37 -06:00
extable.c
fail_function.c
fork.c mm/hugetlb: initialize hugetlb_usage in mm_init 2021-09-08 18:45:53 -07:00
freezer.c sched: Add get_current_state() 2021-06-18 11:43:08 +02:00
futex.c futex: Remove unused variable 'vpid' in futex_proxy_trylock_atomic() 2021-09-03 23:00:22 +02:00
gen_kheaders.sh kbuild: clean up ${quiet} checks in shell scripts 2021-05-27 04:01:50 +09:00
groups.c
hung_task.c Merge branch 'akpm' (patches from Andrew) 2021-07-02 12:08:10 -07:00
iomem.c
irq_work.c irq_work: Make irq_work_queue() NMI-safe again 2021-06-10 10:00:08 +02:00
jump_label.c jump_label: Fix jump_label_text_reserved() vs __init 2021-07-05 10:46:20 +02:00
kallsyms.c module: add printk formats to add module build ID to stacktraces 2021-07-08 11:48:22 -07:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks locking/rwlock: Provide RT variant 2021-08-17 17:50:51 +02:00
Kconfig.preempt sched/core: Disable CONFIG_SCHED_CORE by default 2021-06-28 22:43:05 +02:00
kcov.c
kexec.c kexec: avoid compat_alloc_user_space 2021-09-08 15:32:34 -07:00
kexec_core.c Merge branch 'rework/printk_safe-removal' into for-linus 2021-08-30 16:36:10 +02:00
kexec_elf.c
kexec_file.c kernel: kexec_file: fix error return code of kexec_calculate_store_digests() 2021-05-07 00:26:32 -07:00
kexec_internal.h
kheaders.c
kmod.c modules: add CONFIG_MODPROBE_PATH 2021-05-07 00:26:33 -07:00
kprobes.c Locking fixes: 2021-07-11 11:06:09 -07:00
ksysfs.c
kthread.c Merge branch 'akpm' (patches from Andrew) 2021-06-29 17:29:11 -07:00
latencytop.c
Makefile kbuild: update config_data.gz only when the content of .config is changed 2021-05-02 00:43:35 +09:00
module-internal.h
module.c printk: Userspace format indexing support 2021-07-19 11:57:48 +02:00
module_signature.c
module_signing.c
notifier.c notifier: Remove atomic_notifier_call_chain_robust() 2021-08-16 18:55:32 +02:00
nsproxy.c memcg: enable accounting for new namesapces and struct nsproxy 2021-09-03 09:58:12 -07:00
padata.c padata: Remove repeated verbose license text 2021-08-27 16:30:18 +08:00
panic.c Merge branch 'rework/printk_safe-removal' into for-linus 2021-08-30 16:36:10 +02:00
params.c params: lift param_set_uint_minmax to common code 2021-08-16 14:42:22 +02:00
pid.c kernel/pid.c: implement additional checks upon pidfd_create() parameters 2021-08-10 12:53:07 +02:00
pid_namespace.c memcg: enable accounting for new namesapces and struct nsproxy 2021-09-03 09:58:12 -07:00
profile.c profiling: fix shift-out-of-bounds bugs 2021-09-08 11:50:26 -07:00
ptrace.c sched: Change task_struct::state 2021-06-18 11:43:09 +02:00
range.c
reboot.c reboot: Add hardware protection power-off 2021-06-21 13:08:36 +01:00
regset.c
relay.c
resource.c kernel/resource: fix return code check in __request_free_mem_region 2021-05-14 19:41:32 -07:00
resource_kunit.c
rseq.c rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs() 2021-04-14 18:04:09 +02:00
scftorture.c scftorture: Avoid NULL pointer exception on early exit 2021-07-27 11:39:30 -07:00
scs.c
seccomp.c Merge branch 'exit-cleanups-for-v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2021-09-01 14:52:05 -07:00
signal.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
smp.c smp: Fix all kernel-doc warnings 2021-08-11 14:47:16 +02:00
smpboot.c smpboot: Replace deprecated CPU-hotplug functions. 2021-08-10 14:57:42 +02:00
smpboot.h
softirq.c genirq: Change force_irqthreads to a static key 2021-08-10 22:50:07 +02:00
stackleak.c
stacktrace.c
static_call.c static_call: Fix static_call_text_reserved() vs __init 2021-07-05 10:46:33 +02:00
stop_machine.c stop_machine: Add caller debug info to queue_stop_cpus_work 2021-03-23 16:01:58 +01:00
sys.c Merge branch 'akpm' (patches from Andrew) 2021-09-08 12:55:35 -07:00
sys_ni.c compat: remove some compat entry points 2021-09-08 15:32:35 -07:00
sysctl-test.c kernel/sysctl-test: Remove some casts which are no-longer required 2021-06-23 16:41:24 -06:00
sysctl.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
task_work.c kasan: record task_work_add() call stack 2021-04-30 11:20:42 -07:00
taskstats.c
test_kprobes.c
torture.c torture: Replace deprecated CPU-hotplug functions. 2021-08-10 10:48:07 -07:00
tracepoint.c tracepoint: Fix kerneldoc comments 2021-08-16 11:39:51 -04:00
tsacct.c
ucount.c ucounts: add missing data type changes 2021-08-09 15:45:02 -05:00
uid16.c
uid16.h
umh.c kernel/umh.c: fix some spelling mistakes 2021-05-07 00:26:34 -07:00
up.c A set of locking related fixes and updates: 2021-05-09 13:07:03 -07:00
user-return-notifier.c
user.c fs/epoll: use a per-cpu counter for user's watches count 2021-09-08 11:50:27 -07:00
user_namespace.c memcg: enable accounting for new namesapces and struct nsproxy 2021-09-03 09:58:12 -07:00
usermode_driver.c Merge branch 'work.namei' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2021-07-03 11:41:14 -07:00
utsname.c
utsname_sysctl.c
watch_queue.c
watchdog.c kernel: watchdog: modify the explanation related to watchdog thread 2021-06-29 10:53:46 -07:00
watchdog_hld.c
workqueue.c workqueue: fix state-dump console deadlock 2021-10-11 06:50:28 -10:00
workqueue_internal.h workqueue: Assign a color to barrier work items 2021-08-17 07:49:10 -10:00