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Waiman Long 279749d0d4 sched/debug: Fix cgroup_path[] serialization 
[ Upstream commit ad789f84c9 ]

The handling of sysrq key can be activated by echoing the key to
/proc/sysrq-trigger or via the magic key sequence typed into a terminal
that is connected to the system in some way (serial, USB or other mean).
In the former case, the handling is done in a user context. In the
latter case, it is likely to be in an interrupt context.

Currently in print_cpu() of kernel/sched/debug.c, sched_debug_lock is
taken with interrupt disabled for the whole duration of the calls to
print_*_stats() and print_rq() which could last for the quite some time
if the information dump happens on the serial console.

If the system has many cpus and the sched_debug_lock is somehow busy
(e.g. parallel sysrq-t), the system may hit a hard lockup panic
depending on the actually serial console implementation of the
system.

The purpose of sched_debug_lock is to serialize the use of the global
cgroup_path[] buffer in print_cpu(). The rests of the printk calls don't
need serialization from sched_debug_lock.

Calling printk() with interrupt disabled can still be problematic if
multiple instances are running. Allocating a stack buffer of PATH_MAX
bytes is not feasible because of the limited size of the kernel stack.

The solution implemented in this patch is to allow only one caller at a
time to use the full size group_path[], while other simultaneous callers
will have to use shorter stack buffers with the possibility of path
name truncation. A "..." suffix will be printed if truncation may have
happened.  The cgroup path name is provided for informational purpose
only, so occasional path name truncation should not be a big problem.

Fixes: efe25c2c7b ("sched: Reinstate group names in /proc/sched_debug")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210415195426.6677-1-longman@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-05-14 09:44:26 +02:00
..
bpf bpf: Fix leakage of uninitialized bpf stack under speculation 2021-05-07 10:51:37 +02:00
cgroup cgroup: fix psi monitor for root cgroup 2021-02-17 10:35:14 +01:00
configs
debug kdb: Make memory allocations more robust 2021-03-04 10:26:10 +01:00
dma swiotlb: fix "x86: Don't panic if can not alloc buffer for swiotlb" 2020-11-18 19:20:32 +01:00
events perf/core: Fix unconditional security_locked_down() call 2021-05-07 10:51:38 +02:00
gcov gcov: re-fix clang-11+ support 2021-04-14 08:24:10 +02:00
irq genirq/matrix: Prevent allocation counter corruption 2021-05-11 14:04:05 +02:00
livepatch livepatch: Nullify obj->mod in klp_module_coming()'s error path 2019-08-19 13:03:37 +02:00
locking locking/qrwlock: Fix ordering in queued_write_lock_slowpath() 2021-04-28 13:19:14 +02:00
power PM: EM: postpone creating the debugfs dir till fs_initcall 2021-03-30 14:35:28 +02:00
printk printk: fix deadlock when kernel panic 2021-03-04 10:26:50 +01:00
rcu rcu/nocb: Perform deferred wake up before last idle's need_resched() check 2021-03-04 10:26:47 +01:00
sched sched/debug: Fix cgroup_path[] serialization 2021-05-14 09:44:26 +02:00
time posix-timers: Preserve return value in clock_adjtime32() 2021-05-11 14:04:04 +02:00
trace tracing: Restructure trace_clock_global() to never block 2021-05-11 14:04:18 +02:00
.gitignore kbuild: update config_data.gz only when the content of .config is changed 2021-05-11 14:04:16 +02:00
acct.c acct_on(): don't mess with freeze protection 2019-04-04 21:04:13 -04:00
async.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
audit_fsnotify.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
audit_tree.c fsnotify: switch send_to_group() and ->handle_event to const struct qstr * 2019-04-26 13:51:03 -04:00
audit_watch.c audit: CONFIG_CHANGE don't log internal bookkeeping as an event 2020-10-01 13:17:32 +02:00
audit.c audit: fix a net reference leak in audit_list_rules_send() 2020-06-22 09:30:59 +02:00
audit.h audit: fix a net reference leak in audit_list_rules_send() 2020-06-22 09:30:59 +02:00
auditfilter.c audit: fix a net reference leak in audit_list_rules_send() 2020-06-22 09:30:59 +02:00
auditsc.c audit: enforce op for string fields 2019-05-28 17:46:43 -04:00
backtracetest.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
bounds.c
capability.c LSM: add SafeSetID module that gates setid calls 2019-01-25 11:22:43 -08:00
compat.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
configs.c kernel/configs: Replace GPL boilerplate code with SPDX identifier 2019-07-30 18:34:15 +02:00
context_tracking.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
cpu_pm.c kernel/cpu_pm: Fix uninitted local in cpu_pm 2020-06-22 09:31:22 +02:00
cpu.c kernel/cpu: add arch override for clear_tasks_mm_cpumask() mm handling 2020-12-30 11:50:56 +01:00
crash_core.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 230 2019-06-19 17:09:06 +02:00
crash_dump.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
cred.c keys: Fix request_key() cache 2020-01-17 19:48:42 +01:00
delayacct.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25 2019-05-21 11:52:39 +02:00
dma.c
exec_domain.c
exit.c don't dump the threads that had been already exiting when zapped. 2020-11-18 19:20:31 +01:00
extable.c extable: Add function to search only kernel exception table 2019-08-21 22:23:48 +10:00
fail_function.c fail_function: Remove a redundant mutex unlock 2020-11-24 13:29:18 +01:00
fork.c exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:44:55 +01:00
freezer.c Revert "libata, freezer: avoid block device removal while system is frozen" 2019-10-06 09:11:37 -06:00
futex.c Revert 337f13046f ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op") 2021-05-11 14:04:16 +02:00
gen_kheaders.sh kbuild: add variables for compression tools 2020-09-03 11:27:10 +02:00
groups.c
hung_task.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
iomem.c mm/nvdimm: add is_ioremap_addr and use that to check ioremap address 2019-07-12 11:05:40 -07:00
irq_work.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
jump_label.c jump_label: Don't warn on __exit jump entries 2019-08-29 15:10:10 +01:00
kallsyms.c kallsyms: Refactor kallsyms_show_value() to take cred 2020-07-16 08:16:44 +02:00
kcmp.c exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:44:55 +01:00
Kconfig.freezer treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.hz treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.locks treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.preempt sched/rt, Kconfig: Unbreak def/oldconfig with CONFIG_PREEMPT=y 2019-07-22 18:05:11 +02:00
kcov.c kcov: convert kcov.refcount to refcount_t 2019-03-07 18:32:02 -08:00
kexec_core.c kernel: kexec: remove the lock operation of system_transition_mutex 2021-02-03 23:25:56 +01:00
kexec_elf.c kexec_elf: support 32 bit ELF files 2019-09-06 23:58:44 +02:00
kexec_file.c ima: Free IMA measurement buffer after kexec syscall 2021-03-04 10:26:25 +01:00
kexec_internal.h
kexec.c kexec_load: Disable at runtime if the kernel is locked down 2019-08-19 21:54:15 -07:00
kheaders.c kheaders: Move from proc to sysfs 2019-05-24 20:16:01 +02:00
kmod.c kmod: make request_module() return an error when autoloading is disabled 2020-04-17 10:50:22 +02:00
kprobes.c tracing/kprobe: Fix to support kretprobe events on unloaded modules 2021-02-13 13:52:54 +01:00
ksysfs.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 170 2019-05-30 11:26:39 -07:00
kthread.c kthread: Extract KTHREAD_IS_PER_CPU 2021-02-07 15:35:49 +01:00
latencytop.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
Makefile kbuild: update config_data.gz only when the content of .config is changed 2021-05-11 14:04:16 +02:00
module_signature.c module: harden ELF info handling 2021-04-07 14:47:38 +02:00
module_signing.c module: harden ELF info handling 2021-04-07 14:47:38 +02:00
module-internal.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
module.c modules: inherit TAINT_PROPRIETARY_MODULE 2021-05-11 14:04:04 +02:00
notifier.c kernel/notifier.c: intercept duplicate registrations to avoid infinite loops 2020-10-01 13:17:23 +02:00
nsproxy.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
padata.c padata: add separate cpuhp node for CPUHP_PADATA_DEAD 2020-06-17 16:40:22 +02:00
panic.c panic: ensure preemption is disabled during panic() 2019-10-07 15:47:19 -07:00
params.c lockdown: Lock down module params that specify hardware parameters (eg. ioport) 2019-08-19 21:54:16 -07:00
pid_namespace.c proc/sysctl: add shared variables for range check 2019-07-18 17:08:07 -07:00
pid.c kernel/pid.c: convert struct pid count to refcount_t 2019-07-16 19:23:24 -07:00
profile.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
ptrace.c ptrace: Set PF_SUPERPRIV when checking capability 2020-11-24 13:29:24 +01:00
range.c
reboot.c reboot: fix overflow parsing reboot cpu number 2020-11-18 19:20:30 +01:00
relay.c kernel/relay.c: fix memleak on destroy relay channel 2020-08-26 10:40:51 +02:00
resource.c /dev/mem: Revoke mappings when a driver claims the region 2020-06-24 17:50:35 +02:00
rseq.c signal: Remove task parameter from force_sig 2019-05-27 09:36:28 -05:00
seccomp.c seccomp: Add missing return in non-void function 2021-03-04 10:26:45 +01:00
signal.c ptrace: fix task_join_group_stop() for the case when current is traced 2020-11-10 12:37:24 +01:00
smp.c smp: Warn on function calls from softirq context 2019-07-20 11:27:16 +02:00
smpboot.c kthread: Extract KTHREAD_IS_PER_CPU 2021-02-07 15:35:49 +01:00
smpboot.h
softirq.c Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-07-08 11:01:13 -07:00
stackleak.c stackleak: Mark stackleak_track_stack() as notrace 2018-12-05 19:31:44 -08:00
stacktrace.c stacktrace: Don't skip first entry on noncurrent tasks 2019-11-04 21:19:25 +01:00
stop_machine.c stop_machine: Avoid potential race behaviour 2019-10-17 12:47:12 +02:00
sys_ni.c arch: handle arches who do not yet define clone3 2019-06-21 01:54:53 +02:00
sys.c kernel/sys.c: avoid copying possible padding bytes in copy_to_user 2020-10-01 13:17:23 +02:00
sysctl_binary.c kernel/sysctl: add panic_print into sysctl 2019-01-04 13:13:47 -08:00
sysctl-test.c kernel/sysctl-test: Add null pointer test for sysctl.c:proc_dointvec() 2020-10-01 13:17:10 +02:00
sysctl.c sysctl.c: fix underflow value setting risk in vm_table 2021-03-17 17:03:45 +01:00
task_work.c
taskstats.c taskstats: fix data-race 2020-01-09 10:19:54 +01:00
test_kprobes.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25 2019-05-21 11:52:39 +02:00
torture.c torture: Remove exporting of internal functions 2019-08-01 14:30:22 -07:00
tracepoint.c tracepoint: Do not fail unregistering a probe due to memory failure 2021-03-04 10:26:32 +01:00
tsacct.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
ucount.c proc/sysctl: add shared variables for range check 2019-07-18 17:08:07 -07:00
uid16.c
uid16.h
umh.c usermodehelper: reset umask to default before executing user process 2020-10-14 10:32:58 +02:00
up.c smp: Remove smp_call_function() and on_each_cpu() return values 2019-06-23 14:26:26 +02:00
user_namespace.c Keyrings namespacing 2019-07-08 19:36:47 -07:00
user-return-notifier.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
user.c Keyrings namespacing 2019-07-08 19:36:47 -07:00
utsname_sysctl.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
utsname.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
watchdog_hld.c kernel/watchdog_hld.c: hard lockup message should end with a newline 2019-04-19 09:46:05 -07:00
watchdog.c watchdog/softlockup: Enforce that timestamp is valid on boot 2020-02-24 08:36:52 +01:00
workqueue_internal.h sched/core, workqueues: Distangle worker accounting from rq lock 2019-04-16 16:55:15 +02:00
workqueue.c workqueue: Move the position of debug_work_activate() in __queue_work() 2021-04-14 08:24:17 +02:00