On Mon 17-03-14 10:55:28, Vegard Nossum wrote: > On 03/17/2014 10:51 AM, Michal Hocko wrote: > >On Mon 17-03-14 17:19:33, Xishi Qiu wrote: > >>OS boot failed when set cmdline kmemcheck=1. The reason is that > >>NMI handlers will access the memory from kmalloc(), this will cause > >>page fault, because memory from kmalloc() is tracked by kmemcheck. > >> > >>watchdog_nmi_enable() > >> perf_event_create_kernel_counter() > >> perf_event_alloc() > >> event = kzalloc(sizeof(*event), GFP_KERNEL); > > > >Where is this path called from an NMI context? > > > >Your trace bellow points at something else and it doesn't seem to > >allocate any memory either. It looks more like x86_perf_event_update > >sees an invalid perf_event or something like that... > > > > It's not important that the kzalloc() is called from NMI context, it's > important that the memory that was allocated is touched (read/written) from > NMI context. OK, I see. I thought that kzalloc already touches that memory but my knowledge of kmemcheck is basically zero... Anyway, sorry for the noise. > I'm currently looking into the possibility of handling recursive faults in > kmemcheck (using the approach outlined by peterz; see > https://lkml.org/lkml/2014/2/26/141). > > > Vegard -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>