linux/kernel/events/core.c, branch v6.19

perf: sched: Fix perf crash with new is_user_task() helper

2026-01-30T22:06:07Z

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: 90942f9fac05 ("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 Signed-off-by: Steven Rostedt (Google) Signed-off-by: Peter Zijlstra (Intel) Tested-by: Guenter Roeck Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260129102821.46484722@gandalf.local.home

perf: Fix refcount warning on event->mmap_count increment

2026-01-21T15:28:58Z

When calling refcount_inc(&event->mmap_count) inside perf_mmap_rb(), the following warning is triggered: refcount_t: addition on 0; use-after-free. WARNING: lib/refcount.c:25 PoC: struct perf_event_attr attr = {0}; int fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0); mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); int victim = syscall(__NR_perf_event_open, &attr, 0, -1, fd, PERF_FLAG_FD_OUTPUT); mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED, victim, 0); This occurs when creating a group member event with the flag PERF_FLAG_FD_OUTPUT. The group leader should be mmap-ed and then mmap-ing the event triggers the warning. Since the event has copied the output_event in perf_event_set_output(), event->rb is set. As a result, perf_mmap_rb() calls refcount_inc(&event->mmap_count) when event->mmap_count = 0. Disallow the case when event->mmap_count = 0. This also prevents two events from updating the same user_page. Fixes: 448f97fba901 ("perf: Convert mmap() refcounts to refcount_t") Suggested-by: Peter Zijlstra Signed-off-by: Will Rosenberg Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260119184956.801238-1-whrosenb@asu.edu

Merge tag 'perf-urgent-2026-01-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2026-01-11T16:55:27Z

Pull perf event fix from Ingo Molnar: "Fix perf swevent hrtimer deinit regression" * tag 'perf-urgent-2026-01-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: perf: Ensure swevent hrtimer is properly destroyed

treewide: Update email address

2026-01-11T16:09:11Z

In a vain attempt to consolidate the email zoo switch everything to the kernel.org account. Signed-off-by: Thomas Gleixner Signed-off-by: Linus Torvalds

perf: Ensure swevent hrtimer is properly destroyed

2026-01-05T07:55:54Z

With the change to hrtimer_try_to_cancel() in perf_swevent_cancel_hrtimer() it appears possible for the hrtimer to still be active by the time the event gets freed. Make sure the event does a full hrtimer_cancel() on the free path by installing a perf_event::destroy handler. Fixes: eb3182ef0405 ("perf/core: Fix system hang caused by cpu-clock usage") Reported-by: CyberUnicorns Tested-by: CyberUnicorns Debugged-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel)

perf/core: Fix missing read event generation on task exit

2025-12-09T11:22:25Z

For events with inherit_stat enabled, a "read" event will be generated to collect per task event counts on task exit. The call chain is as follows: do_exit -> perf_event_exit_task -> perf_event_exit_task_context -> perf_event_exit_event -> perf_remove_from_context -> perf_child_detach -> sync_child_event -> perf_event_read_event However, the child event context detaches the task too early in perf_event_exit_task_context, which causes sync_child_event to never generate the read event in this case, since child_event->ctx->task is always set to TASK_TOMBSTONE. Fix that by moving context lock section backward to ensure ctx->task is not set to TASK_TOMBSTONE before generating the read event. Because perf_event_free_task calls perf_event_exit_task_context with exit = false to tear down all child events from the context, and the task never lived, accessing the task PID can lead to a use-after-free. To fix that, let sync_child_event read task from argument and move the call to the only place it should be triggered to avoid the effect of setting ctx->task to TASK_TOMESTONE, and add a task parameter to perf_event_exit_event to trigger the sync_child_event properly when needed. This bug can be reproduced by running "perf record -s" and attaching to any program that generates perf events in its child tasks. If we check the result with "perf report -T", the last line of the report will leave an empty table like "# PID TID", which is expected to contain the per-task event counts by design. Fixes: ef54c1a476ae ("perf: Rework perf_event_exit_event()") Signed-off-by: Thaumy Cheng Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Ian Rogers Cc: James Clark Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: linux-perf-users@vger.kernel.org Link: https://patch.msgid.link/20251209041600.963586-1-thaumy.love@gmail.com

Merge tag 'perf-core-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2025-12-02T04:42:01Z

Pull performance events updates from Ingo Molnar: "Callchain support: - Add support for deferred user-space stack unwinding for perf, enabled on x86. (Peter Zijlstra, Steven Rostedt) - unwind_user/x86: Enable frame pointer unwinding on x86 (Josh Poimboeuf) x86 PMU support and infrastructure: - x86/insn: Simplify for_each_insn_prefix() (Peter Zijlstra) - x86/insn,uprobes,alternative: Unify insn_is_nop() (Peter Zijlstra) Intel PMU driver: - Large series to prepare for and implement architectural PEBS support for Intel platforms such as Clearwater Forest (CWF) and Panther Lake (PTL). (Dapeng Mi, Kan Liang) - Check dynamic constraints (Kan Liang) - Optimize PEBS extended config (Peter Zijlstra) - cstates: - Remove PC3 support from LunarLake (Zhang Rui) - Add Pantherlake support (Zhang Rui) - Clearwater Forest support (Zide Chen) AMD PMU driver: - x86/amd: Check event before enable to avoid GPF (George Kennedy) Fixes and cleanups: - task_work: Fix NMI race condition (Peter Zijlstra) - perf/x86: Fix NULL event access and potential PEBS record loss (Dapeng Mi) - Misc other fixes and cleanups (Dapeng Mi, Ingo Molnar, Peter Zijlstra)" * tag 'perf-core-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (38 commits) perf/x86/intel: Fix and clean up intel_pmu_drain_arch_pebs() type use perf/x86/intel: Optimize PEBS extended config perf/x86/intel: Check PEBS dyn_constraints perf/x86/intel: Add a check for dynamic constraints perf/x86/intel: Add counter group support for arch-PEBS perf/x86/intel: Setup PEBS data configuration and enable legacy groups perf/x86/intel: Update dyn_constraint base on PEBS event precise level perf/x86/intel: Allocate arch-PEBS buffer and initialize PEBS_BASE MSR perf/x86/intel: Process arch-PEBS records or record fragments perf/x86/intel/ds: Factor out PEBS group processing code to functions perf/x86/intel/ds: Factor out PEBS record processing code to functions perf/x86/intel: Initialize architectural PEBS perf/x86/intel: Correct large PEBS flag check perf/x86/intel: Replace x86_pmu.drain_pebs calling with static call perf/x86: Fix NULL event access and potential PEBS record loss perf/x86: Remove redundant is_x86_event() prototype entry,unwind/deferred: Fix unwind_reset_info() placement unwind_user/x86: Fix arch=um build perf: Support deferred user unwind unwind_user/x86: Teach FP unwind about start of function ...

perf: Fix 0 count issue of cpu-clock

2025-11-20T09:42:12Z

Currently cpu-clock event always returns 0 count, e.g., perf stat -e cpu-clock -- sleep 1 Performance counter stats for 'sleep 1': 0 cpu-clock # 0.000 CPUs utilized 1.002308394 seconds time elapsed The root cause is the commit 'bc4394e5e79c ("perf: Fix the throttle error of some clock events")' adds PERF_EF_UPDATE flag check before calling cpu_clock_event_update() to update the count, however the PERF_EF_UPDATE flag is never set when the cpu-clock event is stopped in counting mode (pmu->dev() -> cpu_clock_event_del() -> cpu_clock_event_stop()). This leads to the cpu-clock event count is never updated. To fix this issue, force to set PERF_EF_UPDATE flag for cpu-clock event just like what task-clock does. Fixes: bc4394e5e79c ("perf: Fix the throttle error of some clock events") Signed-off-by: Dapeng Mi Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Ian Rogers Acked-by: Namhyung Kim Link: https://patch.msgid.link/20251112080526.3971392-1-dapeng1.mi@linux.intel.com

perf/core: Fix system hang caused by cpu-clock usage

2025-11-03T10:04:19Z

cpu-clock usage by the async-profiler tool can trigger a system hang, which got bisected back to the following commit by Octavia Togami: 18dbcbfabfff ("perf: Fix the POLL_HUP delivery breakage") causes this issue The root cause of the hang is that cpu-clock is a special type of SW event which relies on hrtimers. The __perf_event_overflow() callback is invoked from the hrtimer handler for cpu-clock events, and __perf_event_overflow() tries to call cpu_clock_event_stop() to stop the event, which calls htimer_cancel() to cancel the hrtimer. But that's a recursion into the hrtimer code from a hrtimer handler, which (unsurprisingly) deadlocks. To fix this bug, use hrtimer_try_to_cancel() instead, and set the PERF_HES_STOPPED flag, which causes perf_swevent_hrtimer() to stop the event once it sees the PERF_HES_STOPPED flag. [ mingo: Fixed the comments and improved the changelog. ] Closes: https://lore.kernel.org/all/CAHPNGSQpXEopYreir+uDDEbtXTBvBvi8c6fYXJvceqtgTPao3Q@mail.gmail.com/ Fixes: 18dbcbfabfff ("perf: Fix the POLL_HUP delivery breakage") Reported-by: Octavia Togami Suggested-by: Peter Zijlstra Signed-off-by: Dapeng Mi Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Tested-by: Octavia Togami Cc: stable@vger.kernel.org Link: https://github.com/lucko/spark/issues/530 Link: https://patch.msgid.link/20251015051828.12809-1-dapeng1.mi@linux.intel.com

perf: Support deferred user unwind

2025-10-29T09:29:58Z

Add support for deferred userspace unwind to perf. Where perf currently relies on in-place stack unwinding; from NMI context and all that. This moves the userspace part of the unwind to right before the return-to-userspace. This has two distinct benefits, the biggest is that it moves the unwind to a faultable context. It becomes possible to fault in debug info (.eh_frame, SFrame etc.) that might not otherwise be readily available. And secondly, it de-duplicates the user callchain where multiple samples happen during the same kernel entry. To facilitate this the perf interface is extended with a new record type: PERF_RECORD_CALLCHAIN_DEFERRED and two new attribute flags: perf_event_attr::defer_callchain - to request the user unwind be deferred perf_event_attr::defer_output - to request PERF_RECORD_CALLCHAIN_DEFERRED records The existing PERF_RECORD_SAMPLE callchain section gets a new context type: PERF_CONTEXT_USER_DEFERRED After which will come a single entry, denoting the 'cookie' of the deferred callchain that should be attached here, matching the 'cookie' field of the above mentioned PERF_RECORD_CALLCHAIN_DEFERRED. The 'defer_callchain' flag is expected on all events with PERF_SAMPLE_CALLCHAIN. The 'defer_output' flag is expect on the event responsible for collecting side-band events (like mmap, comm etc.). Setting 'defer_output' on multiple events will get you duplicated PERF_RECORD_CALLCHAIN_DEFERRED records. Based on earlier patches by Josh and Steven. Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20251023150002.GR4067720@noisy.programming.kicks-ass.net