Hi, Lucas

Thank you for the fix.

On Tue, Dec 17, 2024 at 12:14 PM <devel-request@lists.crash-utility.osci.io> wrote:

Date: Sat, 14 Dec 2024 18:01:14 -0500
From: Lucas Oakley <soakley@redhat.com>
Subject: [Crash-utility] [PATCH] Fix incorrect 'bt -v' output
        suggesting overflow
To: devel@lists.crash-utility.osci.io
Message-ID: <20241214230114.2854910-1-soakley@redhat.com>
Content-Type: text/plain; charset="US-ASCII"; x-default=true

Change check_stack_overflow() to check if the thread_info's cpu
member is smaller than possible existing CPUs, rather than the
kernel table's cpu number (kt->cpus). The kernel table's cpu number
is changed on some architectures to reflect the highest numbered
online cpu + 1. This can cause a false positive in
check_stack_overflow() if the cpu member of a parked task's
thread_info structure, assigned to an offlined cpu, is larger than
the kt->cpus but lower than the number of existing logical cpus.
An example of this is RHEL 7 on s390x or RHEL 8 on ppc64le when
the highest numbered CPU is offlined.

Signed-off-by: Lucas Oakley <soakley@redhat.com>
---
 task.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/task.c b/task.c
index 33de7da..93dab0e 100644
--- a/task.c
+++ b/task.c
@@ -11253,12 +11253,12 @@ check_stack_overflow(void)
                                cpu = 0;
                                break;
                        }
-                       if (cpu >= kt->cpus) {
+                       if (cpu >= get_cpus_present()) {
                                if (!overflow)
                                        print_task_header(fp, tc, 0);
                                fprintf(fp,
                                    "  possible stack overflow: thread_info.cpu: %d >= %d\n",
-                                       cpu, kt->cpus);
+                                       cpu, get_cpus_present());
                                overflow++; total++;
                        }
                }

To avoid calling get_cpus_present() twice, I would tend to modify it as below:

diff --git a/task.c b/task.c
index 33de7da2a692..49f771e275c1 100644
--- a/task.c
+++ b/task.c
@@ -11238,6 +11238,8 @@ check_stack_overflow(void)
                }
 
                if (VALID_MEMBER(thread_info_cpu)) {
+                       int cpus = get_cpus_present();
+
                        switch (cpu_size)
                        {
                        case 1:
@@ -11253,12 +11255,12 @@ check_stack_overflow(void)
                                cpu = 0;
                                break;
                        }
-                       if (cpu >= kt->cpus) {
+                       if (cpu >= cpus) {
                                if (!overflow)
                                        print_task_header(fp, tc, 0);
                                fprintf(fp,
                                    "  possible stack overflow: thread_info.cpu: %d >= %d\n",
-                                       cpu, kt->cpus);
+                                       cpu, cpus);
                                overflow++; total++;
                        }
                }

What do you think?

 Lianbo

--
2.47.1