On Thu, Sep 26, 2024 at 4:47 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, 25 Sep 2024 21:47:32 +0800 Adrian Huang <adrianhuang0701@xxxxxxxxx> wrote: > > > > > ... > > > > From: Adrian Huang <ahuang12@xxxxxxxxxx> > > After re-visiting code path about setting the kasan ptep (pte pointer), > > it's unlikely that a kasan ptep is set and cleared simultaneously by > > different CPUs. So, use ptep_get_and_clear() to get rid of the spinlock > > operation. > > "unlikely" isn't particularly comforting. We'd prefer to never corrupt > pte's! > > I'm suspecting we need a more thorough solution here. > > btw, for a lame fix, did you try moving the spin_lock() into > kasan_release_vmalloc(), around the apply_to_existing_page_range() > call? That would at least reduce locking frequency a lot. Some > mitigation might be needed to avoid excessive hold times. I did try it before. That didn't help. In this case, each iteration in kasan_release_vmalloc_node() only needs to clear one pte. However, vn->purge_list is the long list under the heavy load: 128 cores (128 vmap_nodes) execute kasan_release_vmalloc_node() to clear the corresponding pte(s) while other cores allocate vmalloc space (populate the page table of the vmalloc address) and populate vmalloc shadow page table. Lots of cores contend init_mm.page_table_lock. For a lame fix, adding cond_resched() in the loop of kasan_release_vmalloc_node() is an option. Any suggestions and comments about this issue? Thanks. -- Adrian
