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. 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? 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
