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ad789f84c9
linux-next/kernel
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Waiman Long ad789f84c9 sched/debug: Fix cgroup_path[] serialization 
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
2021-04-21 13:55:42 +02:00
..
bpf bpf: Tighten speculative pointer arithmetic mask 2021-04-16 23:52:01 +02:00
cgroup idmapped-mounts-v5.12 2021-02-23 13:39:45 -08:00
configs staging: ION: remove some references to CONFIG_ION 2021-01-06 17:39:38 +01:00
debug kgdb: fix to kill breakpoints on initmem after boot 2021-02-26 09:41:05 -08:00
dma Merge branch 'stable/for-linus-5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb 2021-02-26 13:59:32 -08:00
entry entry: Explicitly flush pending rcuog wakeup before last rescheduling point 2021-02-17 14:12:43 +01:00
events perf/core: Flush PMU internal buffers for per-CPU events 2021-03-06 12:52:39 +01:00
gcov gcov: clang: fix clang-11+ build 2021-04-16 16:10:37 -07:00
irq genirq: Disable interrupts for force threaded handlers 2021-03-21 00:17:52 +01:00
kcsan kcsan: Rewrite kcsan_prandom_u32_max() without prandom_u32_state() 2021-01-04 14:39:07 -08:00
livepatch kallsyms: refactor {,module_}kallsyms_on_each_symbol 2021-02-08 12:22:08 +01:00
locking Two minor fixes: one for a Clang warning, the other improves an 2021-04-11 11:47:03 -07:00
power PM: EM: postpone creating the debugfs dir till fs_initcall 2021-03-23 19:53:48 +01:00
printk Merge branch 'printk-rework' into for-linus 2021-02-22 13:43:55 +01:00
rcu Scheduler updates for v5.12: 2021-02-21 12:35:04 -08:00
sched sched/debug: Fix cgroup_path[] serialization 2021-04-21 13:55:42 +02:00
time kernel, fs: Introduce and use set_restart_fn() and arch_set_restart_data() 2021-03-16 22:13:10 +01:00
trace tracing/dynevent: Fix a memory link in dyn_event_release() 2021-04-13 18:40:00 -07:00
.gitignore
acct.c kernel/acct.c: use #elif instead of #end and #elif 2020-12-15 22:46:15 -08:00
async.c treewide: Remove uninitialized_var() usage 2020-07-16 12:35:15 -07:00
audit_fsnotify.c audit_alloc_mark(): don't open-code ERR_CAST() 2021-02-23 10:25:27 -05:00
audit_tree.c fsnotify: generalize handle_inode_event() 2020-12-03 14:58:35 +01:00
audit_watch.c fsnotify: generalize handle_inode_event() 2020-12-03 14:58:35 +01:00
audit.c audit: Remove leftover reference to the audit_tasklet 2021-01-15 11:58:10 -05:00
audit.h audit: change unnecessary globals into statics 2020-08-17 20:26:58 -04:00
auditfilter.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
auditsc.c idmapped-mounts-v5.12 2021-02-23 13:39:45 -08:00
backtracetest.c treewide: Replace DECLARE_TASKLET() with DECLARE_TASKLET_OLD() 2020-07-30 11:15:58 -07:00
bounds.c
capability.c capability: handle idmapped mounts 2021-01-24 14:27:16 +01:00
compat.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
configs.c
context_tracking.c context_tracking: Ensure that the critical path cannot be instrumented 2020-06-11 15:14:36 +02:00
cpu_pm.c notifier: Fix broken error handling pattern 2020-09-01 09:58:03 +02:00
cpu.c cpumask: Introduce DYING mask 2021-04-16 17:06:32 +02:00
crash_core.c kdump: append uts_namespace.name offset to VMCOREINFO 2020-12-15 22:46:18 -08:00
crash_dump.c
cred.c
delayacct.c
dma.c
exec_domain.c
exit.c signal: Allow tasks to cache one sigqueue struct 2021-04-14 18:04:08 +02:00
extable.c
fail_function.c fault-injection: handle EI_ETYPE_TRUE 2020-12-15 22:46:19 -08:00
fork.c Linux 5.12-rc8 2021-04-20 10:13:58 +02:00
freezer.c Revert "kernel: freezer should treat PF_IO_WORKER like PF_KTHREAD for freezing" 2021-03-27 14:09:10 -06:00
futex.c kernel, fs: Introduce and use set_restart_fn() and arch_set_restart_data() 2021-03-16 22:13:10 +01:00
gen_kheaders.sh
groups.c groups: simplify struct group_info allocation 2021-02-26 09:41:03 -08:00
hung_task.c kernel/hung_task.c: make type annotations consistent 2020-11-02 12:14:19 -08:00
iomem.c
irq_work.c irq_work: Optimize irq_work_single() 2020-11-24 16:47:49 +01:00
jump_label.c static_call: Fix static_call_update() sanity check 2021-03-19 13:16:44 +01:00
kallsyms.c kallsyms: only build {,module_}kallsyms_on_each_symbol when required 2021-02-08 12:24:04 +01:00
kcmp.c Merge branch 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2020-12-15 19:36:48 -08:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt preempt: Introduce CONFIG_PREEMPT_DYNAMIC 2021-02-17 14:12:24 +01:00
kcov.c kernel: make kcov_common_handle consider the current context 2020-11-02 18:00:20 -08:00
kexec_core.c Merge branch 'work.elf-compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2021-02-21 09:29:23 -08:00
kexec_elf.c
kexec_file.c ima: Free IMA measurement buffer after kexec syscall 2021-02-10 15:49:38 -05:00
kexec_internal.h kexec: move machine_kexec_post_load() to public interface 2021-02-22 12:33:26 +00:00
kexec.c LSM: Introduce kernel_post_load_data() hook 2020-10-05 13:37:03 +02:00
kheaders.c
kmod.c kmod: remove redundant "be an" in the comment 2020-08-12 10:58:01 -07:00
kprobes.c kprobes: Fix to delay the kprobes jump optimization 2021-02-19 14:57:12 -05:00
ksysfs.c
kthread.c - Correct the marking of kthreads which are supposed to run on a specific, 2021-01-24 10:09:20 -08:00
latencytop.c
Makefile kcmp: Support selection of SYS_kcmp without CHECKPOINT_RESTORE 2021-02-16 09:59:41 +01:00
module_signature.c module: harden ELF info handling 2021-01-19 10:24:45 +01:00
module_signing.c module: harden ELF info handling 2021-01-19 10:24:45 +01:00
module-internal.h
module.c module: potential uninitialized return in module_kallsyms_on_each_symbol() 2021-02-10 16:57:04 +01:00
notifier.c notifier: Fix broken error handling pattern 2020-09-01 09:58:03 +02:00
nsproxy.c fixes-v5.11 2020-12-14 16:40:27 -08:00
padata.c padata: fix possible padata_works_lock deadlock 2020-09-04 17:51:55 +10:00
panic.c panic: don't dump stack twice on warn 2020-11-14 11:26:04 -08:00
params.c Modules updates for v5.11 2020-12-17 13:01:31 -08:00
pid_namespace.c fixes-v5.11 2020-12-14 16:40:27 -08:00
pid.c Merge branch 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2020-12-15 19:36:48 -08:00
profile.c
ptrace.c Linux 5.12-rc8 2021-04-20 10:13:58 +02:00
range.c kernel.h: split out min()/max() et al. helpers 2020-10-16 11:11:19 -07:00
reboot.c Revert "PM: ACPI: reboot: Use S5 for reboot" 2021-03-18 16:58:02 +01:00
regset.c regset: kill ->get() 2020-07-27 14:31:12 -04:00
relay.c relay: allow the use of const callback structs 2020-12-15 22:46:18 -08:00
resource_kunit.c resource: provide meaningful MODULE_LICENSE() in test suite 2020-11-25 18:52:35 +01:00
resource.c resource: Move devmem revoke code to resource framework 2021-01-12 14:26:31 +01:00
rseq.c rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs() 2021-04-14 18:04:09 +02:00
scftorture.c scftorture: Add debug output for wrong-CPU warning 2021-01-04 13:53:41 -08:00
scs.c scs: switch to vmapped shadow stacks 2020-12-01 10:30:28 +00:00
seccomp.c seccomp: Improve performace by optimizing rmb() 2021-02-10 12:40:11 -08:00
signal.c Linux 5.12-rc8 2021-04-20 10:13:58 +02:00
smp.c smp: Process pending softirqs in flush_smp_call_function_from_idle() 2021-02-17 14:12:42 +01:00
smpboot.c kthread: Extract KTHREAD_IS_PER_CPU 2021-01-22 15:09:42 +01:00
smpboot.h
softirq.c softirq: Move do_softirq_own_stack() to generic asm header 2021-02-10 23:34:16 +01:00
stackleak.c stackleak: let stack_erasing_sysctl take a kernel pointer buffer 2020-09-19 13:13:39 -07:00
stacktrace.c stacktrace: Remove reliable argument from arch_stack_walk() callback 2020-09-18 14:24:16 +01:00
static_call.c static_call: Fix static_call_update() sanity check 2021-03-19 13:16:44 +01:00
stop_machine.c stop_machine: Add caller debug info to queue_stop_cpus_work 2021-03-23 16:01:58 +01:00
sys_ni.c epoll: wire up syscall epoll_pwait2 2020-12-19 11:18:38 -08:00
sys.c prctl: fix PR_SET_MM_AUXV kernel stack leak 2021-03-14 14:33:27 -07:00
sysctl-test.c
sysctl.c sched: Move SCHED_DEBUG sysctl to debugfs 2021-04-16 17:06:34 +02:00
task_work.c task_work: remove legacy TWA_SIGNAL path 2020-12-12 09:17:38 -07:00
taskstats.c treewide: rename nla_strlcpy to nla_strscpy. 2020-11-16 08:08:54 -08:00
test_kprobes.c
torture.c torture: Maintain torture-specific set of CPUs-online books 2021-01-06 17:17:22 -08:00
tracepoint.c tracepoints: Code clean up 2021-02-09 12:27:29 -05:00
tsacct.c
ucount.c
uid16.c
uid16.h
umh.c usermodehelper: reset umask to default before executing user process 2020-10-06 10:31:52 -07:00
up.c
user_namespace.c fixes-v5.11 2020-12-14 16:40:27 -08:00
user-return-notifier.c
user.c user: Use generic ns_common::count 2020-08-19 14:14:12 +02:00
usermode_driver.c bpf: Fix umd memory leak in copy_process() 2021-03-19 22:23:19 +01:00
utsname_sysctl.c
utsname.c uts: Use generic ns_common::count 2020-08-19 14:13:20 +02:00
watch_queue.c watch_queue: rectify kernel-doc for init_watch() 2021-01-26 11:16:34 +00:00
watchdog_hld.c
watchdog.c workqueue/watchdog: Make unbound workqueues aware of touch_softlockup_watchdog() 2021-04-04 13:26:49 -04:00
workqueue_internal.h
workqueue.c workqueue/watchdog: Make unbound workqueues aware of touch_softlockup_watchdog() 2021-04-04 13:26:49 -04:00