在 2021/8/17 14:14, Greg Kroah-Hartman 写道: > On Tue, Aug 17, 2021 at 09:45:00AM +0800, Chen Huang wrote: >> >> >> 在 2021/8/16 21:35, Greg Kroah-Hartman 写道: >>> On Mon, Aug 16, 2021 at 09:21:11PM +0800, Chen Huang wrote: >>>> >>>> >>>> 在 2021/8/16 16:34, Greg Kroah-Hartman 写道: >>>>> On Mon, Aug 16, 2021 at 07:21:37AM +0000, Chen Huang wrote: >>>>>> From: Roman Gushchin <guro@xxxxxx> >>>>> >>>>> What is the git commit id of this patch in Linus's tree? >>>>> >>>>>> >>>>>> Patch series "mm: allow mapping accounted kernel pages to userspace", v6. >>>>>> >>>>>> Currently a non-slab kernel page which has been charged to a memory cgroup >>>>>> can't be mapped to userspace. The underlying reason is simple: PageKmemcg >>>>>> flag is defined as a page type (like buddy, offline, etc), so it takes a >>>>>> bit from a page->mapped counter. Pages with a type set can't be mapped to >>>>>> userspace. >>>>>> >>>>>> But in general the kmemcg flag has nothing to do with mapping to >>>>>> userspace. It only means that the page has been accounted by the page >>>>>> allocator, so it has to be properly uncharged on release. >>>>>> >>>>>> Some bpf maps are mapping the vmalloc-based memory to userspace, and their >>>>>> memory can't be accounted because of this implementation detail. >>>>>> >>>>>> This patchset removes this limitation by moving the PageKmemcg flag into >>>>>> one of the free bits of the page->mem_cgroup pointer. Also it formalizes >>>>>> accesses to the page->mem_cgroup and page->obj_cgroups using new helpers, >>>>>> adds several checks and removes a couple of obsolete functions. As the >>>>>> result the code became more robust with fewer open-coded bit tricks. >>>>>> >>>>>> This patch (of 4): >>>>>> >>>>>> Currently there are many open-coded reads of the page->mem_cgroup pointer, >>>>>> as well as a couple of read helpers, which are barely used. >>>>>> >>>>>> It creates an obstacle on a way to reuse some bits of the pointer for >>>>>> storing additional bits of information. In fact, we already do this for >>>>>> slab pages, where the last bit indicates that a pointer has an attached >>>>>> vector of objcg pointers instead of a regular memcg pointer. >>>>>> >>>>>> This commits uses 2 existing helpers and introduces a new helper to >>>>>> converts all read sides to calls of these helpers: >>>>>> struct mem_cgroup *page_memcg(struct page *page); >>>>>> struct mem_cgroup *page_memcg_rcu(struct page *page); >>>>>> struct mem_cgroup *page_memcg_check(struct page *page); >>>>>> >>>>>> page_memcg_check() is intended to be used in cases when the page can be a >>>>>> slab page and have a memcg pointer pointing at objcg vector. It does >>>>>> check the lowest bit, and if set, returns NULL. page_memcg() contains a >>>>>> VM_BUG_ON_PAGE() check for the page not being a slab page. >>>>>> >>>>>> To make sure nobody uses a direct access, struct page's >>>>>> mem_cgroup/obj_cgroups is converted to unsigned long memcg_data. >>>>>> >>>>>> Signed-off-by: Roman Gushchin <guro@xxxxxx> >>>>>> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >>>>>> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> >>>>>> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> >>>>>> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> >>>>>> Acked-by: Michal Hocko <mhocko@xxxxxxxx> >>>>>> Link: https://lkml.kernel.org/r/20201027001657.3398190-1-guro@xxxxxx >>>>>> Link: https://lkml.kernel.org/r/20201027001657.3398190-2-guro@xxxxxx >>>>>> Link: https://lore.kernel.org/bpf/20201201215900.3569844-2-guro@xxxxxx >>>>>> >>>>>> Conflicts: >>>>>> mm/memcontrol.c >>>>> >>>>> The "Conflicts:" lines should be removed. >>>>> >>>>> Please fix up the patch series and resubmit. But note, this seems >>>>> really intrusive, are you sure these are all needed? >>>>> >>>> >>>> OK，I will resend the patchset. >>>> Roman Gushchin's patchset formalize accesses to the page->mem_cgroup and >>>> page->obj_cgroups. But for LRU pages and most other raw memcg, they may >>>> pin to a memcg cgroup pointer, which should always point to an object cgroup >>>> pointer. That's the problem I met. And Muchun Song's patchset fix this. >>>> So I think these are all needed. >>> >>> What in-tree driver causes this to happen and under what workload? >>> >>>>> What UIO driver are you using that is showing problems like this? >>>>> >>>> >>>> The UIO driver is my own driver, and it's creation likes this: >>>> First, we register a device >>>> pdev = platform_device_register_simple("uio_driver,0, NULL, 0); >>>> and use uio_info to describe the UIO driver, the page is alloced and used >>>> for uio_vma_fault >>>> info->mem[0].addr = (phys_addr_t) kzalloc(PAGE_SIZE, GFP_ATOMIC); >>> >>> That is not a physical address, and is not what the uio api is for at >>> all. Please do not abuse it that way. >>> >>>> then we register the UIO driver. >>>> uio_register_device(&pdev->dev, info) >>> >>> So no in-tree drivers are having problems with the existing code, only >>> fake ones? >> >> Yes, but the nullptr porblem may not just about uio driver. For now, page struct >> has a union >> union { >> struct mem_cgroup *mem_cgroup; >> struct obj_cgroup **obj_cgroups; >> }; >> For the slab pages, the union info should belong to obj_cgroups. And for user >> pages, it should belong to mem_cgroup. When a slab page changes its obj_cgroups, >> then another user page which is in the same compound page of that slab page will >> gets the wrong mem_cgroup in __mod_lruvec_page_state(), and will trigger nullptr >> in mem_cgroup_lruvec(). Correct me if I'm wrong. Thanks! > > And how can that be triggered by a user in the 5.10.y kernel tree at the > moment? > > I'm all for fixing problems, but this one does not seem like it is an > actual issue for the 5.10 tree right now. Am I missing something? > > thanks, > Sorry, it maybe just the problem of my own driver. Please ignore the patchset. Thanks! > greg k-h > > . >
