[PATCH] stacktrace: Use PF_KTHREAD to check for kernel threads

[PATCH] stacktrace: Use PF_KTHREAD to check for kernel threads

[Thomas Gleixner]

!current->mm is not a reliable indicator for kernel threads as they might
temporarily use a user mm. Check for PF_KTHREAD instead.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -228,7 +228,7 @@ unsigned int stack_trace_save_user(unsig
 	};
 
 	/* Trace user stack if not a kernel thread */
-	if (!current->mm)
+	if (current->flags & PF_KTHREAD)
 		return 0;
 
 	arch_stack_walk_user(consume_entry, &c, task_pt_regs(current));

Re: [PATCH] stacktrace: Use PF_KTHREAD to check for kernel threads

[Mark Rutland]

On Tue, Jul 02, 2019 at 05:53:35PM +0200, Thomas Gleixner wrote:
> !current->mm is not a reliable indicator for kernel threads as they might
> temporarily use a user mm. Check for PF_KTHREAD instead.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

FWIW:

Acked-by: Mark Rutland <mark.rutland@arm.com>

As a heads-up, I started looking into cleaning up bogus mm checks
tree-wide, since there are a number that look suspicious (e.g. arm64's
arch_dup_task_struct() and x86's __kernel_fpu_begin()).

I was hoping to add an is_kthread(tsk) helper to push people in the
right direction [1].

Thanks,
Mark.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=sched/kthread-cleanup

> ---
> --- a/kernel/stacktrace.c
> +++ b/kernel/stacktrace.c
> @@ -228,7 +228,7 @@ unsigned int stack_trace_save_user(unsig
>  	};
>  
>  	/* Trace user stack if not a kernel thread */
> -	if (!current->mm)
> +	if (current->flags & PF_KTHREAD)
>  		return 0;
>  
>  	arch_stack_walk_user(consume_entry, &c, task_pt_regs(current));

[tip:core/stacktrace] stacktrace: Use PF_KTHREAD to check for kernel threads

[tip-bot for Thomas Gleixner]

Commit-ID:  7e8e6816c6495a1168f9a7a50125d82c23e59300
Gitweb:     https://git.kernel.org/tip/7e8e6816c6495a1168f9a7a50125d82c23e59300
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 2 Jul 2019 17:53:35 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 3 Jul 2019 09:04:06 +0200

stacktrace: Use PF_KTHREAD to check for kernel threads

!current->mm is not a reliable indicator for kernel threads as they might
temporarily use a user mm. Check for PF_KTHREAD instead.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1907021750100.1802@nanos.tec.linutronix.de

---
 kernel/stacktrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 36139de0a3c4..c8d0f05721a1 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -228,7 +228,7 @@ unsigned int stack_trace_save_user(unsigned long *store, unsigned int size)
 	};
 
 	/* Trace user stack if not a kernel thread */
-	if (!current->mm)
+	if (current->flags & PF_KTHREAD)
 		return 0;
 
 	arch_stack_walk_user(consume_entry, &c, task_pt_regs(current));