On Wed, 19 Jul 2017, Ethan Barnes wrote: > There is a page fault in cpu hotplug when removing the callbacks for the > last dynamic state. > The last dynamic state will not be removed, causing a page fault when > hotplug thinks the callbacks still exists and calls it. > > The problem is as follows: > - __cpuhp_remove_state() eventually calls cpuhp_store_callbacks() with > NULLs for most params. > - If state is the last state (i.e. CPUHP_AP_ONLINE_DYN or > CPUHP_BP_PREPARE_STATE) then cpuhp_store_callbacks() calls > cpuhp_reserve_state(), which returns the *next* available DYN state. > - The NULLs are stored in that *next* state (i.e. AP_ONLINE_DYN + 1 or > BP_PREPARE_DYN + 1) instead of in AP_ONLINE_DYN or BP_PREPARE_DYN. Thus, > the last state is never cleared. The callbacks now point to invalid memory. > - When the cpu is onlined again and/or offlined, then the invalid > callback is invoked, causing a page fault.
Indeed. > The patch above solves this by detecting when a state is being removed, > and not calling cpuhp_reserve_state(). > > I have brought this up before, but hoping to get some traction on it > this time: > https://lkml.org/lkml/2017/7/5/574 Escaped my attention. > diff --git a/kernel/cpu.c b/kernel/cpu.c > index eee0331..f7fda16 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -1252,7 +1252,8 @@ static int cpuhp_store_callbacks(enum cpuhp_state > state, const char *name, That patch is corrupted by your mail-client or mail-server or both. > struct cpuhp_step *sp; > int ret = 0; > > - if (state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN) { > + if (name && > + (state == CPUHP_AP_ONLINE_DYN || state == > CPUHP_BP_PREPARE_DYN)) { > ret = cpuhp_reserve_state(state); > if (ret < 0) > return ret; > Western Digital Corporation (and its subsidiaries) E-mail Confidentiality > Notice & Disclaimer: > Can you please make sure that there is a blank line before that automatically inserted disclaimer? Thanks, tglx
