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Steven Rostedt 76ed27608f perf: sched: Fix perf crash with new is_user_task() helper 
In order to do a user space stacktrace the current task needs to be a user
task that has executed in user space. It use to be possible to test if a
task is a user task or not by simply checking the task_struct mm field. If
it was non NULL, it was a user task and if not it was a kernel task.

But things have changed over time, and some kernel tasks now have their
own mm field.

An idea was made to instead test PF_KTHREAD and two functions were used to
wrap this check in case it became more complex to test if a task was a
user task or not[1]. But this was rejected and the C code simply checked
the PF_KTHREAD directly.

It was later found that not all kernel threads set PF_KTHREAD. The io-uring
helpers instead set PF_USER_WORKER and this needed to be added as well.

But checking the flags is still not enough. There's a very small window
when a task exits that it frees its mm field and it is set back to NULL.
If perf were to trigger at this moment, the flags test would say its a
user space task but when perf would read the mm field it would crash with
at NULL pointer dereference.

Now there are flags that can be used to test if a task is exiting, but
they are set in areas that perf may still want to profile the user space
task (to see where it exited). The only real test is to check both the
flags and the mm field.

Instead of making this modification in every location, create a new
is_user_task() helper function that does all the tests needed to know if
it is safe to read the user space memory or not.

[1] https://lore.kernel.org/all/20250425204120.639530125@goodmis.org/

Fixes: 90942f9fac ("perf: Use current->flags & PF_KTHREAD|PF_USER_WORKER instead of current->mm == NULL")
Closes: https://lore.kernel.org/all/0d877e6f-41a7-4724-875d-0b0a27b8a545@roeck-us.net/
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260129102821.46484722@gandalf.local.home
2026-01-30 23:06:07 +01:00
..
bpf bpf: Reject BPF_MAP_TYPE_INSN_ARRAY in check_reg_const_str() 2026-01-07 19:03:46 -08:00
cgroup kernel: cgroup: Add LGPL-2.1 SPDX license ID to legacy_freezer.c 2026-01-15 22:03:15 -10:00
configs hung_task: panic when there are more than N hung tasks at the same time 2025-11-12 10:00:14 -08:00
debug kdb: Adapt kdb_msg_write to work with NBCON consoles 2025-10-24 12:56:20 +02:00
dma dma/pool: Avoid allocating redundant pools 2026-01-14 11:00:00 +01:00
entry rseq: Switch to TIF_RSEQ if supported 2025-11-04 08:35:37 +01:00
events perf: sched: Fix perf crash with new is_user_task() helper 2026-01-30 23:06:07 +01:00
futex Futex changes for v6.19: 2025-12-10 17:21:30 +09:00
gcov gcov: add support for GCC 15 2025-11-09 21:19:44 -08:00
irq treewide: Update email address 2026-01-11 06:09:11 -10:00
kcsan Kernel Concurrency Sanitizer (KCSAN) updates for v6.18 2025-10-02 08:31:44 -07:00
livepatch livepatching changes for 6.19 2025-12-03 13:46:48 -08:00
liveupdate kho: validate preserved memory map during population 2026-01-14 22:16:21 -08:00
locking RCU pull request for v6.19 2025-12-03 12:18:07 -08:00
module kernel: modules: Add SPDX license identifier to kmod.c 2026-01-15 16:58:28 -08:00
power Merge branch 'pm-em' 2026-01-16 16:16:24 +01:00
printk printk fixup for 6.19 rc6 2026-01-16 09:46:59 -08:00
rcu RCU pull request for v6.19 2025-12-03 12:18:07 -08:00
sched sched/fair: Revert force wakeup preemption 2026-01-23 11:53:20 +01:00
time clocksource: Reduce watchdog readout delay limit to prevent false positives 2026-01-21 11:33:11 +01:00
trace function_graph: Fix args pointer mismatch in print_graph_retval() 2026-01-23 13:34:38 -05:00
unwind unwind_user/x86: Teach FP unwind about start of function 2025-10-29 10:29:58 +01:00
.gitignore kheaders: rebuild kheaders_data.tar.xz when a file is modified within a minute 2025-06-24 20:30:37 +09:00
acct.c act: use credential guards in acct_write_process() 2025-11-04 12:36:49 +01:00
async.c
audit.c audit: fix skb leak when audit rate limit is exceeded 2025-09-10 19:55:00 -04:00
audit.h audit: fix comment misindentation in audit.h 2025-10-22 19:28:06 -04:00
audit_fsnotify.c VFS/audit: introduce kern_path_parent() for audit 2025-09-23 12:37:35 +02:00
audit_tree.c mount-related stuff for this cycle 2025-10-03 10:19:44 -07:00
audit_watch.c VFS/audit: introduce kern_path_parent() for audit 2025-09-23 12:37:35 +02:00
auditfilter.c audit: Use kzalloc() instead of kmalloc()/memset() in audit_krule_to_data() 2025-11-07 16:38:34 -05:00
auditsc.c audit: merge loops in __audit_inode_child() 2025-11-07 16:50:42 -05:00
backtracetest.c
bounds.c x86/asm: Remove ANNOTATE_DATA_SPECIAL usage 2025-12-03 16:53:19 +01:00
capability.c capability: Remove unused has_capability 2025-03-07 22:03:09 -06:00
cfi.c cfi: Move BPF CFI types and helpers to generic code 2025-07-31 18:23:53 -07:00
compat.c
configs.c
context_tracking.c context_tracking: Make RCU watch ct_kernel_exit_state() warning 2025-03-04 18:44:29 -08:00
cpu.c cpu: Make atomic hotplug callbacks run with interrupts disabled on UP 2025-12-10 15:49:11 +09:00
cpu_pm.c syscore: Pass context data to callbacks 2025-11-14 10:01:52 +01:00
crash_core.c crash: fix crashkernel resource shrink 2025-11-15 10:52:01 -08:00
crash_core_test.c crash: add KUnit tests for crash_exclude_mem_range 2025-09-13 17:32:55 -07:00
crash_dump_dm_crypt.c crash_dump: retrieve dm crypt keys in kdump kernel 2025-05-21 10:48:21 -07:00
crash_reserve.c crash: let architecture decide crash memory export to iomem_resource 2025-11-12 10:00:15 -08:00
cred.c kernel-6.19-rc1.cred 2025-12-01 13:45:41 -08:00
delayacct.c delayacct: remove redundant code and adjust indentation 2025-05-27 19:40:33 -07:00
dma.c
elfcorehdr.c
exec_domain.c
exit.c Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
exit.h
extable.c
fail_function.c
fork.c Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
freezer.c freezer: Clarify that only cgroup1 freezer uses PM freezer 2025-10-30 20:10:27 +01:00
gen_kheaders.sh kheaders: make it possible to override TAR 2025-08-06 10:23:36 +09:00
groups.c
hung_task.c hung_task: add hung_task_sys_info sysctl to dump sys info on task-hung 2025-11-20 14:03:43 -08:00
iomem.c mm/memremap: Pass down MEMREMAP_* flags to arch_memremap_wb() 2025-02-21 15:05:38 +01:00
irq_work.c kasan: make kasan_record_aux_stack_noalloc() the default behaviour 2025-01-13 22:40:36 -08:00
jump_label.c jump_label: Use RCU in all users of __module_text_address(). 2025-03-10 11:54:46 +01:00
kallsyms.c kallsyms: Fix wrong "big" kernel symbol type read from procfs 2025-11-24 16:56:24 +01:00
kallsyms_internal.h
kallsyms_selftest.c kallsyms: use kmalloc_array() instead of kmalloc() 2025-09-28 11:36:14 -07:00
kallsyms_selftest.h
kcmp.c kcmp: improve performance adding an unlikely hint to task comparisons 2025-02-21 10:25:33 +01:00
Kconfig.freezer
Kconfig.hz kernel: Fix "select" wording on HZ_250 description 2025-02-21 09:20:30 +01:00
Kconfig.kexec liveupdate: kho: move to kernel/liveupdate 2025-11-27 14:24:33 -08:00
Kconfig.locks
Kconfig.preempt softirq: Allow to drop the softirq-BKL lock on PREEMPT_RT 2025-09-17 16:25:41 +02:00
kcov.c kcov: use write memory barrier after memcpy() in kcov_move_area() 2025-09-13 17:32:44 -07:00
kexec.c kexec: enable CMA based contiguous allocation 2025-08-02 12:01:38 -07:00
kexec_core.c kernel/kexec: fix IMA when allocation happens in CMA area 2025-12-23 11:23:14 -08:00
kexec_elf.c kexec: initialize ELF lowest address to ULONG_MAX 2025-03-16 22:30:47 -07:00
kexec_file.c x86/kexec: carry forward the boot DTB on kexec 2025-09-13 17:32:43 -07:00
kexec_internal.h kexec: enable CMA based contiguous allocation 2025-08-02 12:01:38 -07:00
kheaders.c kheaders: Simplify attribute through __BIN_ATTR_SIMPLE_RO() 2024-12-24 09:46:49 +01:00
kprobes.c kprobes: Add missing kerneldoc for __get_insn_slot 2025-07-15 18:45:34 +09:00
kstack_erase.c sysctl: remove __user qualifier from stack_erasing_sysctl buffer argument 2025-11-27 15:44:53 +01:00
ksyms_common.c
ksysfs.c kexec: move sysfs entries to /sys/kernel/kexec 2025-11-27 14:24:42 -08:00
kthread.c kthread: Warn if mm_struct lacks user_ns in kthread_use_mm() 2025-12-24 21:32:58 +01:00
latencytop.c treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
Makefile liveupdate: kho: move to kernel/liveupdate 2025-11-27 14:24:33 -08:00
module_signature.c
notifier.c reboot: move reboot_notifier_list to kernel/reboot.c 2024-11-05 17:12:31 -08:00
nscommon.c ns: rename is_initial_namespace() 2025-11-11 10:01:31 +01:00
nsproxy.c nsproxy: fix free_nsproxy() and simplify create_new_namespaces() 2025-11-14 13:10:38 +01:00
nstree.c nstree: fix kernel-doc comments for internal functions 2025-11-14 13:10:38 +01:00
padata.c padata: remove __padata_list_init() 2025-11-14 18:15:49 +08:00
panic.c panic: only warn about deprecated panic_print on write access 2026-01-19 12:30:01 -08:00
params.c params: Replace deprecated strcpy() with strscpy() and memcpy() 2025-08-16 21:47:25 +02:00
pid.c ns: drop custom reference count initialization for initial namespaces 2025-11-11 10:01:32 +01:00
pid_namespace.c pid: rely on common reference count behavior 2025-11-11 10:01:32 +01:00
pid_sysctl.h treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
profile.c
ptrace.c rseq: Introduce struct rseq_data 2025-11-04 08:30:50 +01:00
range.c
reboot.c - The 7 patch series "powerpc/crash: use generic crashkernel 2025-04-01 10:06:52 -07:00
regset.c
relay.c relay: update relay to use mmap_prepare 2025-11-16 17:28:11 -08:00
resource.c Reinstate "resource: avoid unnecessary lookups in find_next_iomem_res()" 2025-11-27 14:24:45 -08:00
resource_kunit.c
rseq.c rseq: Switch to fast path processing on exit to user 2025-11-04 08:34:39 +01:00
scftorture.c scftorture: Handle NULL argument passed to scf_add_to_free_list(). 2024-11-14 16:09:51 -08:00
scs.c scs: fix a wrong parameter in __scs_magic 2025-11-12 10:00:13 -08:00
seccomp.c Performance events updates for v6.18: 2025-09-30 11:11:21 -07:00
signal.c signal: Move MMCID exit out of sighand lock 2025-11-25 19:45:40 +01:00
smp.c smp: Introduce a helper function to check for pending IPIs 2025-11-19 18:06:50 +01:00
smpboot.c sched/smp: Use the SMP version of idle_thread_set_boot_cpu() 2025-06-13 08:47:20 +02:00
smpboot.h
softirq.c softirq: Allow to drop the softirq-BKL lock on PREEMPT_RT 2025-09-17 16:25:41 +02:00
stacktrace.c
static_call.c
static_call_inline.c Modules changes for 6.15-rc1 2025-03-30 15:44:36 -07:00
stop_machine.c sched/core: Fix migrate_swap() vs. hotplug 2025-07-01 15:02:03 +02:00
sys.c Patch series in this pull request: 2025-10-02 18:44:54 -07:00
sys_ni.c uprobes/x86: Add uprobe syscall to speed up uprobe 2025-08-21 20:09:20 +02:00
sysctl-test.c sysctl: move u8 register test to lib/test_sysctl.c 2025-04-14 14:13:41 +02:00
sysctl.c sysctl: Wrap do_proc_douintvec with the public function proc_douintvec_conv 2025-11-27 15:45:38 +01:00
task_work.c task_work: Fix NMI race condition 2025-10-29 10:29:54 +01:00
taskstats.c fdget(), more trivial conversions 2024-11-03 01:28:06 -05:00
torture.c torture: Delay CPU-hotplug operations until boot completes 2025-08-14 15:26:30 -07:00
tracepoint.c tracepoint: Print the function symbol when tracepoint_debug is set 2025-03-21 15:30:10 -04:00
tsacct.c pid: change bacct_add_tsk() to use task_ppid_nr_ns() 2025-08-19 13:38:20 +02:00
ucount.c ucount: use atomic_long_try_cmpxchg() in atomic_long_inc_below() 2025-08-02 12:01:38 -07:00
uid16.c
uid16.h
umh.c treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
up.c
user-return-notifier.c
user.c ns: drop custom reference count initialization for initial namespaces 2025-11-11 10:01:32 +01:00
user_namespace.c ns: move ns type into struct ns_common 2025-09-25 09:23:54 +02:00
utsname.c namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
utsname_sysctl.c treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
vhost_task.c vhost: Take a reference on the task in struct vhost_task. 2025-09-21 17:44:20 -04:00
vmcore_info.c vmcoreinfo: track and log recoverable hardware errors 2025-11-27 14:24:44 -08:00
watch_queue.c watch_queue: Use local kmap in post_one_notification() 2025-11-19 12:17:28 +01:00
watchdog.c powerpc/watchdog: add support for hardlockup_sys_info sysctl 2026-01-14 22:16:22 -08:00
watchdog_buddy.c watchdog: fix opencoded cpumask_next_wrap() in watchdog_next_cpu() 2025-07-31 11:28:03 -04:00
watchdog_perf.c watchdog: skip checks when panic is in progress 2025-09-13 17:32:53 -07:00
workqueue.c workqueue: Don't rely on wq->rescuer to stop rescuer 2025-11-21 09:45:36 -10:00
workqueue_internal.h