Hi Ji Zhang, On Thu, Mar 22, 2018 at 11:06:00AM +0800, Ji Zhang wrote: > When we dump the backtrace of some specific task, there is a potential race > condition due to the task may be running on other cores if SMP enabled. > That is because for current implementation, if the task is not the current > task, we will get the registers used for unwind from cpu_context saved in > thread_info, which is the snapshot before context switch, but if the task > is running on other cores, the registers and the content of stack are > changed. > This may cause that we get the wrong backtrace or incomplete backtrace or > even crash the kernel. > To avoid this case, do not dump the backtrace of the tasks which are > running on other cores. > This patch cannot solve the issue completely but can shrink the window of > race condition. > > Signed-off-by: Ji Zhang <ji.zh...@mediatek.com> > --- > arch/arm64/kernel/traps.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > index eb2d151..95749364 100644 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -113,6 +113,9 @@ void dump_backtrace(struct pt_regs *regs, struct > task_struct *tsk) > if (tsk == current) { > frame.fp = (unsigned long)__builtin_frame_address(0); > frame.pc = (unsigned long)dump_backtrace; > + else if (tsk->state == TASK_RUNNING) {
Missing closing brace. Does this build? > + pr_notice("Do not dump other running tasks\n"); > + return; > } else { > /* > * task blocked in __switch_to baruch -- http://baruch.siach.name/blog/ ~. .~ Tk Open Systems =}------------------------------------------------ooO--U--Ooo------------{= - bar...@tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -