On 2025-04-24 13:28, Steven Rostedt wrote:
On Thu, 24 Apr 2025 18:36:07 +0200
Peter Zijlstra <[email protected]> wrote:
+++ b/kernel/events/callchain.c
@@ -246,22 +246,20 @@ get_perf_callchain(struct pt_regs *regs, bool kernel,
bool user,
if (user) {
if (!user_mode(regs)) {
- if (current->mm)
- regs = task_pt_regs(current);
- else
- regs = NULL;
+ if (!current->mm)
+ goto exit_put;
+ regs = task_pt_regs(current);
I'm thinking this might be one of those is-kthread test written as
has-mm, and they're broken.
Notably things like the io-uring kthreads do have mm.
Can a kthread such as io-uring have user_mode(regs) == true ?
Would there ever be a case where:
current->mm == NULL && !(current->flags & PF_KTHREAD)
?
That is, do we still need to check for current->mm if it's not a kernel
thread, or can we assume it exists?
The case I'd be careful about is if the code can nest over exit_mm()
(e.g. interrupt) after it sets current->mm = NULL.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
