+ scripts-gdb-fix-detection-of-current-cpu-in-kgdb.patch added to mm-nonmm-unstable branch

+ scripts-gdb-fix-detection-of-current-cpu-in-kgdb.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: scripts/gdb: fix detection of current CPU in KGDB
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     scripts-gdb-fix-detection-of-current-cpu-in-kgdb.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/scripts-gdb-fix-detection-of-current-cpu-in-kgdb.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Florian Rommel <mail@florommel.de>
Subject: scripts/gdb: fix detection of current CPU in KGDB
Date: Thu, 25 Apr 2024 17:35:01 +0200

Directly read the current CPU number from the kgdb_active variable.

Before, the active CPU was obtained through the current task, which
required searching the task list for the pid of GDB's selected thread. 
Obtaining the pid was buggy: GDB may use selected_thread().ptid[1] (LWPID)
instead of .ptid[2] (TID) to store the threads pid; see
https://sourceware.org/gdb/current/onlinedocs/gdb.html/Threads-In-Python.html
As a result, the detection could return the wrong CPU number, leading to
incorrect results for $lx_per_cpu and $lx_current.

As a side effect, the patch significantly speeds up $lx_per_cpu and
$lx_current in KGDB by avoiding the task-list iteration.

Link: https://lkml.kernel.org/r/20240425153501.749966-5-mail@florommel.de
Signed-off-by: Florian Rommel <mail@florommel.de>
Cc: Andrew Jones <ajones@ventanamicro.com>
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 scripts/gdb/linux/cpus.py |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/scripts/gdb/linux/cpus.py~scripts-gdb-fix-detection-of-current-cpu-in-kgdb
+++ a/scripts/gdb/linux/cpus.py
@@ -26,11 +26,7 @@ def get_current_cpu():
     if utils.get_gdbserver_type() == utils.GDBSERVER_QEMU:
         return gdb.selected_thread().num - 1
     elif utils.get_gdbserver_type() == utils.GDBSERVER_KGDB:
-        tid = gdb.selected_thread().ptid[2]
-        if tid > (0x100000000 - MAX_CPUS - 2):
-            return 0x100000000 - tid - 2
-        else:
-            return tasks.get_thread_info(tasks.get_task_by_pid(tid))['cpu']
+        return gdb.parse_and_eval("kgdb_active.counter")
     else:
         raise gdb.GdbError("Sorry, obtaining the current CPU is not yet "
                            "supported with this gdb server.")
_

Patches currently in -mm which might be from mail@florommel.de are

scripts-gdb-fix-failing-kgdb-detection-during-probe.patch
scripts-gdb-fix-parameter-handling-in-lx_per_cpu.patch
scripts-gdb-make-get_thread_info-accept-pointers.patch
scripts-gdb-fix-detection-of-current-cpu-in-kgdb.patch