On Tue, 2012-03-06 at 11:27 +0100, Vegard Nossum wrote: > On 6 March 2012 11:09, Li Zhong <zhong@xxxxxxxxxxxxxxxxxx> wrote: > > This patch tries to fix the problem of page fault exception caused by > > accessing nmiaction structure in nmi if kmemcheck is enabled. > > > > If kmemcheck is enabled, the memory allocated through slab are in pages > > that are marked non-present, so that some checks could be done in the > > page fault handling code ( e.g. whether the memory is read before > > written to ). > > As nmiaction is allocated in this way, so it resides in a non-present > > page. Then there is a page fault while the nmi code accessing the > > nmiaction structure, which would then cause a warning by > > WARN_ON_ONCE(in_nmi()) in kmemcheck_fault(), called by do_page_fault(). > > > > v2: as Peter suggested, changed the nmiaction to use static storage. > > > > v3: as Peter suggested, use macro to shorten the codes. Also keep the > > original usage of register_nmi_handler, so users of this call doesn't > > need change. > > > > Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx> > > Looks like you've solved this now. Thanks. There is still one place [2/2] not solved ... and I guess it might need the way you suggested below. > > For the record, another way to prevent the page fault from happening > in the first place is to set up a new slab cache with the flag > SLAB_NOTRACK. This is different from the GFP_NOTRACK flag which, as > you noted, doesn't prevent page faults, just inhibits > checking/warnings for those memory areas. > > It's a bit of a hassle, I admit. Maybe we could create an additional, > separate set of slab caches (using SLAB_NOTRACK) and a new GFP flag > which selects this set of caches instead. This would allow anything > that takes a gfp_t to allocate memory that is guaranteed not to page > fault when using kmemcheck. Pekka, any thoughts? > I'm not sure whether I understand it correctly? If CONFIG_KMEMCHECK is enabled, create another two sets of malloc_sizes caches, one for cs_cachep, one for cs_dmacachep, both with SLAB_NOTRACK flag. Create a new GFP flag, like __GFP_NO_PF for those places where page fault is not allowed, and return memory from the caches created above. This new GFP flag is set to 0 if CONFIG_KMEMCHECK is not enabled. I think there shouldn't be many such cases, so most of these caches wouldn't actually be used ... Thanks, Zhong > > Vegard > -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
