On Tue, Dec 8, 2015 at 7:05 PM, Alexei Starovoitov <alexei.starovoi...@gmail.com> wrote: > On Tue, Dec 08, 2015 at 06:56:23PM +0100, Dmitry Vyukov wrote: >> On Tue, Dec 8, 2015 at 6:54 PM, Alexei Starovoitov >> <alexei.starovoi...@gmail.com> wrote: >> > On Tue, Dec 08, 2015 at 05:12:04PM +0100, Dmitry Vyukov wrote: >> >> On Tue, Dec 8, 2015 at 4:24 AM, Alexei Starovoitov >> >> <alexei.starovoi...@gmail.com> wrote: >> >> > On Mon, Dec 07, 2015 at 05:09:21PM +0100, Dmitry Vyukov wrote: >> >> >> > So it would be _awesome_ if we could somehow extend this callchain to >> >> >> > include the site that calls call_rcu(). >> >> >> >> >> >> We have a patch for KASAN in works that adds so-called stack depot >> >> >> which allows to map a stack trace onto uint32 id. Then we can plumb >> >> > >> >> > I was hacking something similar to categorize stack traces with u32 id. >> >> > How are you planning to limit the number of such stack traces ? >> >> > and what is the interface for user space to get stack trace from an id? >> >> >> >> >> >> We don't limit number of stack traces. Kernel does not seem to use >> >> data-driven recursion extensively, so there is limited number of >> >> stacks. Though, probably we will need to strip non-interrupt part for >> >> interrupt stacks, otherwise that can produce unbounded number of >> >> different stacks. >> >> There is no interface for user-space, it is used only inside of kernel >> >> to save stacks for memory blocks (rcu callbacks, thread pool items in >> >> the future). >> >> The design is based on what we successfully and extensively use in >> >> user-space sanitizers for years. Current code is here: >> >> https://github.com/ramosian-glider/kasan/commit/fb0eefd212366401ed5ad244233ef379a27bfb46 >> > >> > why did you pick approach to never free accumulated stacks? >> > That limits usability a lot, since once kasan starts using it only >> > reboot will free the memory. ouch. >> > what worked for user space doesn't work for kernel. >> >> >> Freeing and reusing will slow down and complicate code significantly. >> And it is not yet proved to be necessary. > > It's a joke, right? allocating kernel pages without ability to free?!
The plan is to smash kernel much earlier than it will run out of memory. I think this scheme will work pretty well. I've counted 34403 calls to kmalloc/kfree/kmem_cache_alloc/kmem_cache_free in kernel. Multiply this by 2 to account for different stacks leading to the same malloc/free and assuming that we store 16-byte header and 20 4-byte frames, this gives us about 6MB. I can live with that. I can live with 60MB as well. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/