Re: [RESEND][PATCH 3/5] perf: Use current->flags & PF_KTHREAD|PF_USER_WORKER instead of current->mm == NULL
From: Guenter Roeck <linux@roeck-us.net>
Date: 2026-01-27 22:29:39
Also in:
linux-perf-users, lkml
On 1/27/26 07:22, Steven Rostedt wrote:
On Mon, 26 Jan 2026 17:32:35 -0800 Guenter Roeck [off-list ref] wrote:quoted
Still crashing, though not as often and with a slightly different backtrace. I added the backtrace to the bug report @ Google.I figured there would be other locations. A while ago I had a patch to wrap the checks in a "is_user_thread()" helper function[1], but Ingo had issues with it. It seems now it's biting us in the butt and let's see if it would help now. I modified it slightly. [1] https://lore.kernel.org/linux-trace-kernel/20250425204313.616425861@goodmis.org/ (local) If the below fixes it, I'll resend it, but now as a real bug fix.
All attempts to reproduce the problem after applying the patch below failed, so feel free to go ahead and add Tested-by: Guenter Roeck <linux@roeck-us.net> to the patch. Thanks, Guenter
quoted hunk ↗ jump to hunk
-- Stevediff --git a/include/linux/sched.h b/include/linux/sched.h index da0133524d08..5f00b5ed0f3b 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h@@ -1776,6 +1776,11 @@ static __always_inline bool is_percpu_thread(void) (current->nr_cpus_allowed == 1); } +static __always_inline bool is_user_task(struct task_struct *task) +{ + return task->mm && !(task->flags & (PF_KTHREAD | PF_USER_WORKER)); +} + /* Per-process atomic flags. */ #define PFA_NO_NEW_PRIVS 0 /* May not gain new privileges. */ #define PFA_SPREAD_PAGE 1 /* Spread page cache over cpuset */diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index 1f6589578703..9d24b6e0c91f 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c@@ -246,7 +246,7 @@ 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)) + if (!is_user_task(current)) goto exit_put; regs = task_pt_regs(current); }diff --git a/kernel/events/core.c b/kernel/events/core.c index a0fa488bce84..8cca80094624 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c@@ -7460,7 +7460,7 @@ static void perf_sample_regs_user(struct perf_regs *regs_user, if (user_mode(regs)) { regs_user->abi = perf_reg_abi(current); regs_user->regs = regs; - } else if (!(current->flags & (PF_KTHREAD | PF_USER_WORKER))) { + } else if (is_user_task(current)) { perf_get_regs_user(regs_user, regs); } else { regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE;@@ -8100,7 +8100,7 @@ static u64 perf_virt_to_phys(u64 virt) * Try IRQ-safe get_user_page_fast_only first. * If failed, leave phys_addr as 0. */ - if (!(current->flags & (PF_KTHREAD | PF_USER_WORKER))) { + if (is_user_task(current)) { struct page *p; pagefault_disable();@@ -8215,7 +8215,7 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs) { bool kernel = !event->attr.exclude_callchain_kernel; bool user = !event->attr.exclude_callchain_user && - !(current->flags & (PF_KTHREAD | PF_USER_WORKER)); + is_user_task(current); /* Disallow cross-task user callchains. */ bool crosstask = event->ctx->task && event->ctx->task != current; bool defer_user = IS_ENABLED(CONFIG_UNWIND_USER) && user &&