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Tiezhu YangandGreg Kroah-Hartman
040f278cc1
commit677d4a52d4upstream. When testing the kernel live patching with "modprobe livepatch-sample", there is a timeout over 15 seconds from "starting patching transition" to "patching complete". The dmesg command shows "unreliable stack" for user tasks in debug mode, here is one of the messages: livepatch: klp_try_switch_task: bash:1193 has an unreliable stack The "unreliable stack" is because it can not unwind from do_syscall() to its previous frame handle_syscall(). It should use fp to find the original stack top due to secondary stack in do_syscall(), but fp is not used for some other functions, then fp can not be restored by the next frame of do_syscall(), so it is necessary to save fp if task is not current, in order to get the stack top of do_syscall(). Here are the call chains: klp_enable_patch() klp_try_complete_transition() klp_try_switch_task() klp_check_and_switch_task() klp_check_stack() stack_trace_save_tsk_reliable() arch_stack_walk_reliable() When executing "rmmod livepatch-sample", there exists a similar issue. With this patch, it takes a short time for patching and unpatching. Before: # modprobe livepatch-sample # dmesg -T | tail -3 [Sat Sep 6 11:00:20 2025] livepatch: 'livepatch_sample': starting patching transition [Sat Sep 6 11:00:35 2025] livepatch: signaling remaining tasks [Sat Sep 6 11:00:36 2025] livepatch: 'livepatch_sample': patching complete # echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled # rmmod livepatch_sample rmmod: ERROR: Module livepatch_sample is in use # rmmod livepatch_sample # dmesg -T | tail -3 [Sat Sep 6 11:06:05 2025] livepatch: 'livepatch_sample': starting unpatching transition [Sat Sep 6 11:06:20 2025] livepatch: signaling remaining tasks [Sat Sep 6 11:06:21 2025] livepatch: 'livepatch_sample': unpatching complete After: # modprobe livepatch-sample # dmesg -T | tail -2 [Tue Sep 16 16:19:30 2025] livepatch: 'livepatch_sample': starting patching transition [Tue Sep 16 16:19:31 2025] livepatch: 'livepatch_sample': patching complete # echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled # rmmod livepatch_sample # dmesg -T | tail -2 [Tue Sep 16 16:19:36 2025] livepatch: 'livepatch_sample': starting unpatching transition [Tue Sep 16 16:19:37 2025] livepatch: 'livepatch_sample': unpatching complete Cc: stable@vger.kernel.org # v6.9+ Fixes:199cc14cb4("LoongArch: Add kernel livepatching support") Reported-by: Xi Zhang <zhangxi@kylinos.cn> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.