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From: Qian Cai <cai@lca.pw>
To: Alexander Potapenko <glider@google.com>
Cc: Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Marco Elver <elver@google.com>,
	Eric Biggers <ebiggers@google.com>,
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	Vegard Nossum <vegard.nossum@oracle.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
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	Vasily Gorbik <gor@linux.ibm.com>,
	Wolfram Sang <wsa@the-dreams.de>
Subject: Re: [PATCH RFC v3 18/36] kmsan: disable LOCK_DEBUGGING_SUPPORT
Date: Wed, 4 Dec 2019 13:03:18 -0500
Message-ID: <35EF55C2-C46E-4853-8BA8-0F113DD13812@lca.pw> (raw)
In-Reply-To: <CAG_fn=UhprbSxTW-CVsxKfrwOt-p2OEnbLa+R0Xs2coJ+699bw@mail.gmail.com>



> On Dec 4, 2019, at 11:24 AM, Alexander Potapenko <glider@google.com> wrote:
> 
> One can think of KMSAN as a _fast_ replacement of kmemcheck.
> Unfortunately, the latter bit-rotted at some point and was deleted
> from the kernel (I don't think distro debug kernels ever used it
> though).
> 
> From our experience building userspace tools, making KMSAN and KASAN
> work together isn't worth it.
> The resulting monster will be slower than any of the two tools and
> will be using more memory than both of them together.
> This means that anyone who's using at least two machines for fuzzing
> or continuous integration will prefer running two different tools on
> them instead of running KMSAN+KASAN together on every machine.
> 
> That said, I'll try my best to keep existing low-overhead debug
> configs working with KMSAN, but it still won't solve the need of
> running orthogonal kernel configs for testing.

The problem is that we have too many memory-related debugging options in kernel. Those tend to break over time mainly because not many paid kernel developers would care about them, and most of Kernel developers nowadays are paid.  Not many employers would like Google to spend money on long-term health of the kernel because those debugging options does not generate revenues. For example, kmemleak was broken on NUMA for many releases and lockdep PROVE_LOCKING still has too many unfixed splats right now which would render it almost useless for general debugging because it will disable itself after found a splat.

Every of those does somewhat different and yet have many overlapping that yet nobody put any effort to consolidate them. It is even more cumbersome for the options to break without notice because it does not play well with popular ones like KASAN given code for those features are spanning all over the kernel code base, so they are sensitive to changes from other subsystems. It put a burden for bug hunters to enable them because it is going to be expensive increasing test runs time exponentially and maintenance cost of different debug kernels.

  reply index

Thread overview: 120+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-22 11:25 [PATCH RFC v3 00/36] Add KernelMemorySanitizer infrastructure glider
2019-11-22 11:25 ` [PATCH RFC v3 01/36] stackdepot: check depot_index before accessing the stack slab glider
2019-11-27 14:22   ` Marco Elver
2019-11-22 11:25 ` [PATCH RFC v3 02/36] stackdepot: build with -fno-builtin glider
2019-11-27 14:22   ` Marco Elver
2019-11-22 11:25 ` [PATCH RFC v3 03/36] kasan: stackdepot: move filter_irq_stacks() to stackdepot.c glider
2019-11-27 14:22   ` Marco Elver
2019-11-27 14:56     ` Alexander Potapenko
2019-11-22 11:25 ` [PATCH RFC v3 04/36] stackdepot: reserve 5 extra bits in depot_stack_handle_t glider
2019-11-27 14:23   ` Marco Elver
2019-11-22 11:25 ` [PATCH RFC v3 05/36] kmsan: add ReST documentation glider
2019-11-27 14:22   ` Marco Elver
2019-12-03 12:42     ` Alexander Potapenko
2019-11-22 11:25 ` [PATCH RFC v3 06/36] kmsan: gfp: introduce __GFP_NO_KMSAN_SHADOW glider
2019-11-27 14:48   ` Marco Elver
2019-12-03 12:57     ` Alexander Potapenko
2019-11-22 11:25 ` [PATCH RFC v3 07/36] kmsan: introduce __no_sanitize_memory and __SANITIZE_MEMORY__ glider
2019-11-28 13:13   ` Marco Elver
2019-11-29 16:09   ` Andrey Konovalov
2019-12-16 11:35     ` Alexander Potapenko
2019-11-22 11:25 ` [PATCH RFC v3 08/36] kmsan: reduce vmalloc space glider
2019-11-28 13:30   ` Marco Elver
2019-11-22 11:25 ` [PATCH RFC v3 09/36] kmsan: add KMSAN bits to struct page and struct task_struct glider
2019-11-28 13:44   ` Marco Elver
2019-11-28 14:05     ` Alexander Potapenko
2019-11-22 11:25 ` [PATCH RFC v3 10/36] kmsan: add KMSAN runtime glider
2019-11-24 19:44   ` Wolfram Sang
2019-11-25  9:14     ` Alexander Potapenko
2019-11-29 16:07   ` Marco Elver
2019-12-19 14:16     ` Alexander Potapenko
2019-12-02 15:39   ` Andrey Konovalov
2019-12-20 18:58     ` Alexander Potapenko
2019-12-03 14:34   ` Andrey Konovalov
2019-11-22 11:25 ` [PATCH RFC v3 11/36] kmsan: stackdepot: don't allocate KMSAN metadata for stackdepot glider
2019-11-29 14:52   ` Andrey Konovalov
2019-12-03 14:27     ` Alexander Potapenko
2019-11-22 11:25 ` [PATCH RFC v3 12/36] kmsan: define READ_ONCE_NOCHECK() glider
2019-12-02 10:03   ` Marco Elver
2019-12-03 12:45     ` Alexander Potapenko
2019-11-22 11:25 ` [PATCH RFC v3 13/36] kmsan: make READ_ONCE_TASK_STACK() return initialized values glider
2019-12-02 10:07   ` Marco Elver
2019-12-05 15:52     ` Alexander Potapenko
2019-11-22 11:25 ` [PATCH RFC v3 14/36] kmsan: x86: sync metadata pages on page fault glider
2019-11-22 11:26 ` [PATCH RFC v3 15/36] kmsan: add tests for KMSAN glider
2019-11-29 14:14   ` Andrey Konovalov
2019-12-05 14:30     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 16/36] crypto: kmsan: disable accelerated configs under KMSAN glider
2019-12-02 13:25   ` Marco Elver
2019-12-05 14:51     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 17/36] kmsan: x86: disable UNWINDER_ORC " glider
2019-12-02 13:30   ` Marco Elver
2019-11-22 11:26 ` [PATCH RFC v3 18/36] kmsan: disable LOCK_DEBUGGING_SUPPORT glider
2019-12-02 13:33   ` Marco Elver
2019-12-03 14:34     ` Alexander Potapenko
2019-12-03 15:00       ` Qian Cai
2019-12-03 15:14         ` Alexander Potapenko
2019-12-03 18:02           ` Qian Cai
2019-12-03 18:38           ` Steven Rostedt
2019-12-04  8:41             ` Alexander Potapenko
2019-12-04 12:22               ` Petr Mladek
2019-12-04 13:12                 ` Qian Cai
2019-12-04 16:24                   ` Alexander Potapenko
2019-12-04 18:03                     ` Qian Cai [this message]
2019-11-22 11:26 ` [PATCH RFC v3 20/36] kmsan: x86: increase stack sizes in KMSAN builds glider
2019-12-02 14:31   ` Marco Elver
2019-11-22 11:26 ` [PATCH RFC v3 21/36] kmsan: disable KMSAN instrumentation for certain kernel parts glider
2019-11-29 15:07   ` Andrey Konovalov
2019-12-10 10:35     ` Alexander Potapenko
2019-12-10 12:38       ` Alexander Potapenko
2019-12-10 12:43       ` Qian Cai
2019-11-22 11:26 ` [PATCH RFC v3 22/36] kmsan: mm: call KMSAN hooks from SLUB code glider
2019-12-02 15:36   ` Marco Elver
2019-12-10 12:07     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 23/36] kmsan: call KMSAN hooks where needed glider
2019-11-26 10:17   ` Petr Mladek
2019-11-26 10:52     ` Alexander Potapenko
2019-11-29 16:21   ` Andrey Konovalov
2019-12-16 11:30     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 24/36] kmsan: disable instrumentation of certain functions glider
2019-11-29 14:59   ` Andrey Konovalov
2019-12-18 10:02     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 25/36] kmsan: unpoison |tlb| in arch_tlb_gather_mmu() glider
2019-11-29 15:08   ` Andrey Konovalov
2019-12-03 14:19     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 26/36] kmsan: use __msan_memcpy() where possible glider
2019-11-29 15:13   ` Andrey Konovalov
2019-12-05 15:46     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 27/36] kmsan: hooks for copy_to_user() and friends glider
2019-11-29 15:34   ` Andrey Konovalov
2019-12-05 16:00     ` Alexander Potapenko
2019-12-05 16:44       ` Andrey Konovalov
2019-12-11 14:22         ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 28/36] kmsan: enable KMSAN builds glider
2019-11-29 15:55   ` Andrey Konovalov
2019-12-11 12:51     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 29/36] kmsan: handle /dev/[u]random glider
2019-11-22 11:26 ` [PATCH RFC v3 30/36] kmsan: virtio: check/unpoison scatterlist in vring_map_one_sg() glider
2019-11-22 11:26 ` [PATCH RFC v3 31/36] kmsan: disable strscpy() optimization under KMSAN glider
2019-12-02 15:51   ` Marco Elver
2019-12-02 16:23     ` Alexander Potapenko
2019-12-03 11:19       ` Alexander Potapenko
2019-12-03 11:24         ` Marco Elver
2019-12-03 11:27           ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 32/36] kmsan: add iomap support glider
2019-12-03 12:50   ` Marco Elver
2019-12-03 14:07     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 33/36] kmsan: dma: unpoison memory mapped by dma_direct_map_page() glider
2019-11-22 11:26 ` [PATCH RFC v3 34/36] kmsan: disable physical page merging in biovec glider
2019-12-03 12:54   ` Marco Elver
2019-12-03 13:38     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 35/36] kmsan: ext4: skip block merging logic in ext4_mpage_readpages for KMSAN glider
2019-11-25 16:05   ` Robin Murphy
2019-11-25 17:03     ` Alexander Potapenko
2019-12-03 14:22   ` Marco Elver
2019-12-05 14:31     ` Alexander Potapenko
2019-11-22 11:26 ` [PATCH RFC v3 36/36] net: kasan: kmsan: support CONFIG_GENERIC_CSUM on x86, enable it for KASAN/KMSAN glider
2019-12-03 14:17   ` Marco Elver
2019-12-05 14:37     ` Alexander Potapenko
2019-11-29 14:39 ` [PATCH RFC v3 00/36] Add KernelMemorySanitizer infrastructure Marco Elver
2019-12-02 16:02   ` Alexander Potapenko

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