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@xxxxxxxxxxxx>
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@xxxxxxxxxxxx
Signed-off-by: Florian Rommel <mail@xxxxxxxxxxxx>
Cc: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
Cc: Deepak Gupta <debug@xxxxxxxxxxxx>
Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Cc: Kieran Bingham <kbingham@xxxxxxxxxx>
Cc: Kuan-Ying Lee <Kuan-Ying.Lee@xxxxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxxxx 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
