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Mike Galbraith c096a3d44e futex: Handle transient "ownerless" rtmutex state correctly 
commit 9f5d1c336a10c0d24e83e40b4c1b9539f7dba627 upstream.

Gratian managed to trigger the BUG_ON(!newowner) in fixup_pi_state_owner().
This is one possible chain of events leading to this:

Task Prio       Operation
T1   120	lock(F)
T2   120	lock(F)   -> blocks (top waiter)
T3   50 (RT)	lock(F)   -> boosts T1 and blocks (new top waiter)
XX   		timeout/  -> wakes T2
		signal
T1   50		unlock(F) -> wakes T3 (rtmutex->owner == NULL, waiter bit is set)
T2   120	cleanup   -> try_to_take_mutex() fails because T3 is the top waiter
     			     and the lower priority T2 cannot steal the lock.
     			  -> fixup_pi_state_owner() sees newowner == NULL -> BUG_ON()

The comment states that this is invalid and rt_mutex_real_owner() must
return a non NULL owner when the trylock failed, but in case of a queued
and woken up waiter rt_mutex_real_owner() == NULL is a valid transient
state. The higher priority waiter has simply not yet managed to take over
the rtmutex.

The BUG_ON() is therefore wrong and this is just another retry condition in
fixup_pi_state_owner().

Drop the locks, so that T3 can make progress, and then try the fixup again.

Gratian provided a great analysis, traces and a reproducer. The analysis is
to the point, but it confused the hell out of that tglx dude who had to
page in all the futex horrors again. Condensed version is above.

[ tglx: Wrote comment and changelog ]

Fixes: c1e2f0eaf0 ("futex: Avoid violating the 10th rule of futex")
Reported-by: Gratian Crisan <gratian.crisan@ni.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87a6w6x7bb.fsf@ni.com
Link: https://lore.kernel.org/r/87sg9pkvf7.fsf@nanos.tec.linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-11-10 12:35:58 +01:00
..
bpf bpf: Fix a rcu warning for bpffs map pretty-print 2020-10-01 13:14:52 +02:00
cgroup cgroup: add missing skcd->no_refcnt check in cgroup_sk_clone() 2020-08-19 08:14:47 +02:00
configs kconfig: tinyconfig: remove stale stack protector fixups 2018-06-15 07:15:28 +09:00
debug kgdb: Make "kgdbcon" work properly with "kgdb_earlycon" 2020-11-05 11:08:41 +01:00
dma dma-debug: add a schedule point in debug_dma_dump_mappings() 2020-01-04 19:12:43 +01:00
events perf: Fix task_function_call() error handling 2020-10-14 10:31:26 +02:00
gcov gcov: add support for GCC 10.1 2020-09-17 13:45:31 +02:00
irq genirq/matrix: Deal with the sillyness of for_each_cpu() on UP 2020-09-03 11:24:29 +02:00
livepatch livepatch: Nullify obj->mod in klp_module_coming()'s error path 2019-10-07 18:57:10 +02:00
locking locking/lockdep: Fix overflow in presentation of average lock-time 2020-09-03 11:24:21 +02:00
power PM: hibernate: remove the bogus call to get_gendisk() in software_resume() 2020-10-30 10:38:28 +01:00
printk printk: handle blank console arguments passed in. 2020-10-01 13:14:45 +02:00
rcu rcu: Avoid data-race in rcu_gp_fqs_check_wake() 2020-02-11 04:33:55 -08:00
sched sched/features: Fix !CONFIG_JUMP_LABEL case 2020-10-30 10:38:25 +01:00
time timekeeping: Prevent 32bit truncation in scale64_check_overflow() 2020-10-01 13:14:36 +02:00
trace tracing: Fix out of bounds write in get_trace_buf 2020-11-10 12:35:58 +01:00
.gitignore
acct.c acct_on(): don't mess with freeze protection 2019-05-31 06:46:05 -07:00
async.c
audit.c audit: fix a net reference leak in audit_list_rules_send() 2020-06-22 09:05:13 +02:00
audit.h audit: fix a net reference leak in audit_list_rules_send() 2020-06-22 09:05:13 +02:00
audit_fsnotify.c fsnotify: add fsnotify_add_inode_mark() wrappers 2018-05-18 14:58:22 +02:00
audit_tree.c audit: Embed key into chunk 2019-12-13 08:51:11 +01:00
audit_watch.c audit: CONFIG_CHANGE don't log internal bookkeeping as an event 2020-10-01 13:14:33 +02:00
auditfilter.c audit: fix a net reference leak in audit_list_rules_send() 2020-06-22 09:05:13 +02:00
auditsc.c audit: print empty EXECVE args 2019-12-01 09:17:17 +01:00
backtracetest.c
bounds.c kbuild: fix kernel/bounds.c 'W=1' warning 2018-11-13 11:08:47 -08:00
capability.c LSM: generalize flag passing to security_capable 2020-01-23 08:21:29 +01:00
compat.c make 'user_access_begin()' do 'access_ok()' 2020-06-22 09:04:58 +02:00
configs.c
context_tracking.c
cpu.c sched/core: Fix illegal RCU from offline CPUs 2020-06-22 09:05:14 +02:00
cpu_pm.c kernel/cpu_pm: Fix uninitted local in cpu_pm 2020-06-22 09:05:28 +02:00
crash_core.c kernel/crash_core.c: print timestamp using time64_t 2018-08-22 10:52:47 -07:00
crash_dump.c
cred.c memcg: account security cred as well to kmemcg 2020-01-09 10:19:00 +01:00
delayacct.c delayacct: Use raw_spinlocks 2018-04-27 14:34:51 +02:00
dma.c proc: introduce proc_create_single{,_data} 2018-05-16 07:23:35 +02:00
elfcore.c kernel/elfcore.c: include proper prototypes 2019-10-11 18:21:23 +02:00
exec_domain.c proc: introduce proc_create_single{,_data} 2018-05-16 07:23:35 +02:00
exit.c exit: Move preemption fixup up, move blocking operations down 2020-06-22 09:05:14 +02:00
extable.c
fail_function.c bpf/error-inject/kprobes: Clear current_kprobe and enable preempt in kprobe 2018-06-21 12:33:19 +02:00
fork.c mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary 2020-10-29 09:55:15 +01:00
freezer.c PM / reboot: Eliminate race between reboot and suspend 2018-08-06 12:35:20 +02:00
futex.c futex: Handle transient "ownerless" rtmutex state correctly 2020-11-10 12:35:58 +01:00
groups.c
hung_task.c kernel: hung_task.c: disable on suspend 2019-04-20 09:16:02 +02:00
iomem.c memremap: split devm_memremap_pages() and memremap() infrastructure 2018-05-15 23:08:33 -07:00
irq_work.c irq_work: Do not raise an IPI when queueing work on the local CPU 2019-05-31 06:46:19 -07:00
jump_label.c jump_label: move 'asm goto' support test to Kconfig 2019-06-04 08:02:34 +02:00
kallsyms.c kallsyms: Refactor kallsyms_show_value() to take cred 2020-07-16 08:17:26 +02:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt kconfig: include kernel/Kconfig.preempt from init/Kconfig 2018-08-02 08:06:54 +09:00
kcov.c kernel/kcov.c: mark write_comp_data() as notrace 2019-02-12 19:47:20 +01:00
kexec.c kexec: add call to LSM hook in original kexec_load syscall 2018-07-16 12:31:57 -07:00
kexec_core.c kexec: Allocate decrypted control pages for kdump if SME is enabled 2019-11-24 08:20:29 +01:00
kexec_file.c treewide: Use array_size() in vzalloc() 2018-06-12 16:19:22 -07:00
kexec_internal.h
kmod.c kmod: make request_module() return an error when autoloading is disabled 2020-04-17 10:48:52 +02:00
kprobes.c kprobes: Fix compiler warning for !CONFIG_KPROBES_ON_FTRACE 2020-10-01 13:14:54 +02:00
ksysfs.c
kthread.c kthread_worker: prevent queuing delayed work from timer_fn when it is being canceled 2020-11-10 12:35:58 +01:00
latencytop.c
Makefile y2038: futex: Move compat implementation into futex.c 2019-12-01 09:17:38 +01:00
memremap.c mm/memory_hotplug: shrink zones when offlining memory 2020-01-29 16:43:27 +01:00
module-internal.h modsign: log module name in the event of an error 2018-07-02 11:36:17 +02:00
module.c module: Correctly truncate sysfs sections output 2020-08-21 11:05:34 +02:00
module_signing.c modsign: log module name in the event of an error 2018-07-02 11:36:17 +02:00
notifier.c x86/mm: split vmalloc_sync_all() 2020-03-25 08:06:13 +01:00
nsproxy.c
padata.c padata: purge get_cpu and reorder_via_wq from padata_do_serial 2020-05-27 17:37:36 +02:00
panic.c kernel/panic.c: do not append newline to the stack protector panic string 2019-12-01 09:17:10 +01:00
params.c kernel/params.c: downgrade warning for unsafe parameters 2018-04-11 10:28:37 -07:00
pid.c Fix failure path in alloc_pid() 2019-01-13 09:51:06 +01:00
pid_namespace.c signal/pid_namespace: Fix reboot_pid_ns to use send_sig not force_sig 2019-07-26 09:14:01 +02:00
profile.c
ptrace.c ptrace: reintroduce usage of subjective credentials in ptrace_has_cap() 2020-01-23 08:21:29 +01:00
range.c
reboot.c PM / reboot: Eliminate race between reboot and suspend 2018-08-06 12:35:20 +02:00
relay.c kernel/relay.c: fix memleak on destroy relay channel 2020-08-26 10:30:59 +02:00
resource.c resource: fix locking in find_next_iomem_res() 2019-09-16 08:22:20 +02:00
rseq.c rseq: uapi: Declare rseq_cs field as union, update includes 2018-07-10 22:18:52 +02:00
seccomp.c LSM: generalize flag passing to security_capable 2020-01-23 08:21:29 +01:00
signal.c ptrace: fix task_join_group_stop() for the case when current is traced 2020-11-10 12:35:53 +01:00
smp.c cpu/hotplug: Fix "SMT disabled by BIOS" detection for KVM 2019-02-12 19:47:25 +01:00
smpboot.c smpboot: Remove cpumask from the API 2018-07-03 09:20:44 +02:00
smpboot.h
softirq.c nohz: Fix missing tick reprogram when interrupting an inline softirq 2018-08-03 15:52:10 +02:00
stacktrace.c
stop_machine.c Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-08-13 11:25:07 -07:00
sys.c kernel/sys.c: avoid copying possible padding bytes in copy_to_user 2020-10-01 13:14:29 +02:00
sys_ni.c Merge branch 'core-rseq-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-06-10 10:17:09 -07:00
sysctl.c kernel: sysctl: make drop_caches write-only 2020-01-04 19:13:17 +01:00
sysctl_binary.c staging: irda: remove remaining remants of irda code removal 2018-04-16 11:26:49 +02:00
task_work.c
taskstats.c taskstats: fix data-race 2020-01-09 10:18:59 +01:00
test_kprobes.c kprobes: Remove jprobe API implementation 2018-06-21 12:33:05 +02:00
torture.c torture: Keep old-school dmesg format 2018-06-25 11:30:10 -07:00
tracepoint.c tracepoint: Fix tracepoint array element size mismatch 2018-10-17 15:35:29 -04:00
tsacct.c
ucount.c
uid16.c
uid16.h
umh.c usermodehelper: reset umask to default before executing user process 2020-10-14 10:31:21 +02:00
up.c
user-return-notifier.c
user.c userns: use irqsave variant of refcount_dec_and_lock() 2018-08-22 10:52:47 -07:00
user_namespace.c userns: also map extents in the reverse map to kernel IDs 2018-11-13 11:09:00 -08:00
utsname.c uts: create "struct uts_namespace" from kmem_cache 2018-04-11 10:28:35 -07:00
utsname_sysctl.c sys: don't hold uts_sem while accessing userspace memory 2018-08-11 02:05:53 -05:00
watchdog.c watchdog/softlockup: Enforce that timestamp is valid on boot 2020-02-24 08:34:49 +01:00
watchdog_hld.c watchdog: Mark watchdog touch functions as notrace 2018-08-30 12:56:40 +02:00
workqueue.c workqueue: don't use wq_select_unbound_cpu() for bound works 2020-03-18 07:14:20 +01:00
workqueue_internal.h workqueue: Set worker->desc to workqueue name by default 2018-05-18 08:47:13 -07:00