Messages in this thread | | | Date | Fri, 23 Jul 2021 12:29:25 +0800 | From | Jisheng Zhang <> | Subject | Re: [PATCH -next v2] riscv: add VMAP_STACK overflow detection |
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On Fri, 23 Jul 2021 09:36:47 +0800 tongtiangen <tongtiangen@huawei.com> wrote:
> On 2021/7/23 7:54, Jisheng Zhang wrote: > > On Thu, 22 Jul 2021 17:42:52 +0200 > > Andreas Schwab <schwab@linux-m68k.org> wrote: > > > >> On Jul 22 2021, Jisheng Zhang wrote: > >> > >>> I think we need to pin the stack before calling get_wchan(), could you please > >>> try below patch? > >> > >> Thanks, this fixes the crash for me. > >> > >> Andreas. > >> > > > > Thanks for testing. I will send out formal patch later > > > > Thanks > > > > . > > > > Hi all: > I tried to reproduced this crash in openSUSE code repo( > https://github.com/opensuse/kernel ), but not reproduced successfully. > > From the patch of problem repair, the crash is due to task->stack is > released before calling get_wchan, the task state of maybe TASK_DEAD. > > VMAP_STACK is used to detect kernel stack overflow, there is no > connection between the two, it makes me a little confused.
I believe the bug exists from the first day of riscv mainlined.
Since THREAD_INFO_IN_TASK=y in riscv, so when task stack can be freed before being destroyed.
When VMAP_STACK=n, task's stack is allocated from linear mapping. When task stack is freed, the corresponding mapping still exists, and since get_wchan() only read, no harm is observed so far.
When VMAP_STACK=y, task's stack is allocated from vmalloc area. When task stack is freed, the corresponding mapping may not exist, so I expect MMU fault here, thus the kernel panic.
In summary, the bug isn't related with VMAP_STACK, but VMAP_STACK makes the bug observable.
Thanks
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