Re: [RESEND][PATCH 3/5] perf: Use current->flags & PF_KTHREAD|PF_USER_WORKER instead of current->mm == NULL
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2026-01-26 17:18:06
Also in:
linux-perf-users, lkml
Subsystem:
performance events subsystem, the rest · Maintainers:
Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Linus Torvalds
On Mon, 26 Jan 2026 12:05:53 -0500 Steven Rostedt [off-list ref] wrote:
I guess we need to also test for !current->mm because the flags set for an exiting task is done when we can still do callchains. Thus, the only way to know if it is safe to do a callchain when a task is exiting is via task->mm and not task->flags :-/
Can you test this patch? -- Steve
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 1f6589578703..c82d61d73bd8 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c@@ -246,7 +246,14 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, if (user && !crosstask) { if (!user_mode(regs)) { - if (current->flags & (PF_KTHREAD | PF_USER_WORKER)) + /* + * Testing current->mm is not enough as some kernel threads + * may have one set. But testing the flags is not enough + * either as this can be called after a user task + * frees its mm just before it exits. + */ + if (!current->mm || + (current->flags & (PF_KTHREAD | PF_USER_WORKER))) goto exit_put; regs = task_pt_regs(current); }