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([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2da788d1db1sm3145888a91.44.2024.09.04.12.56.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Sep 2024 12:56:34 -0700 (PDT) Sender: Guenter Roeck Message-ID: <274f253a-e44e-431b-9dd3-a499843be96f@roeck-us.net> Date: Wed, 4 Sep 2024 12:56:33 -0700 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/damon/tests/vaddr-kunit: don't use mas_lock for MM_MT_FLAGS-initialized maple tree To: "Liam R. Howlett" , SeongJae Park , Andrew Morton , "Matthew Wilcox (Oracle)" , David Hildenbrand , Brendan Higgins , David Gow , damon@lists.linux.dev, linux-mm@kvack.org, kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240904005815.1388-1-sj@kernel.org> <20240904011840.973-1-sj@kernel.org> <54zu64vxrhdxr4wtmwbewga44shu4f7lz4ffx2hxhag46b56hn@qgrgfrb6mhbv> Content-Language: en-US From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/4/24 12:26, Liam R. Howlett wrote: > * Guenter Roeck [240904 00:27]: >> On 9/3/24 20:36, Liam R. Howlett wrote: >>> * Guenter Roeck [240903 22:38]: >>>> On 9/3/24 19:31, Liam R. Howlett wrote: >>>>> * SeongJae Park [240903 21:18]: >>>>>> On Tue, 3 Sep 2024 17:58:15 -0700 SeongJae Park wrote: >>>>>> >>>>>>> On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" wrote: >>>>>>> >>>>>>>> * SeongJae Park [240903 20:45]: >>>>>>>>> damon_test_three_regions_in_vmas() initializes a maple tree with >>>>>>>>> MM_MT_FLAGS. The flags contains MT_FLAGS_LOCK_EXTERN, which means >>>>>>>>> mt_lock of the maple tree will not be used. And therefore the maple >>>>>>>>> tree initialization code skips initialization of the mt_lock. However, >>>>>>>>> __link_vmas(), which adds vmas for test to the maple tree, uses the >>>>>>>>> mt_lock. In other words, the uninitialized spinlock is used. The >>>>>>>>> problem becomes celar when spinlock debugging is turned on, since it >>>>>>>>> reports spinlock bad magic bug. Fix the issue by not using the mt_lock >>>>>>>>> as promised. >>>>>>>> >>>>>>>> You can't do this, lockdep will tell you this is wrong. >>>>>>> >>>>>>> Hmm, but lockdep was silence on my setup? >>>>>>> >>>>>>>> We need a lock and to use the lock for writes. >>>>>>> >>>>>>> This code is executed by a single-thread test code. Do we still need the lock? >>>>>>> >>>>>>>> >>>>>>>> I'd suggest using different flags so the spinlock is used. >>>>>>> >>>>>>> The reporter mentioned simply dropping MT_FLAGS_LOCK_EXTERN from the flags >>>>>>> causes suspicious RCU usage message. May I ask if you have a suggestion of >>>>>>> better flags? >>>>> >>>>> That would be the lockdep complaining, so that's good. >>>>> >>>>>> >>>>>> I was actually thinking replacing the mt_init_flags() with mt_init(), which >>>>>> same to mt_init_flags() with zero flag, like below. >>>>> >>>>> Yes. This will use the spinlock which should fix your issue, but it >>>>> will use a different style of maple tree. >>>>> >>>>> Perhaps use MT_FLAGS_ALLOC_RANGE to use the same type of maple tree, if >>>>> you ever add threading you will want the rcu flag as well >>>>> (MT_FLAGS_USE_RCU). >>>>> >>>>> I would recommend those two and just use the spinlock. >>>>> >>>> >>>> I tried that (MT_FLAGS_ALLOC_RANGE | MT_FLAGS_USE_RCU). it also triggers >>>> the suspicious RCU usage message. >>>> >>> >>> I am running ./tools/testing/kunit/kunit.py run '*damon*' --arch x86_64 --raw >>> with: >>> CONFIG_LOCKDEP=y >>> CONFIG_DEBUG_SPINLOCK=y >>> >>> and I don't have any issue with locking in the existing code. How do I >>> recreate this issue? >>> >> >> I tested again, and I still see >> >> >> [ 6.233483] ok 4 damon >> [ 6.234190] KTAP version 1 >> [ 6.234263] # Subtest: damon-operations >> [ 6.234335] # module: vaddr >> [ 6.234384] 1..6 >> [ 6.235726] >> [ 6.235931] ============================= >> [ 6.236018] WARNING: suspicious RCU usage >> [ 6.236280] 6.11.0-rc6-00029-gda66250b210f-dirty #1 Tainted: G N >> [ 6.236398] ----------------------------- >> [ 6.236474] lib/maple_tree.c:832 suspicious rcu_dereference_check() usage! >> [ 6.236579] >> [ 6.236579] other info that might help us debug this: >> [ 6.236579] >> [ 6.236738] >> [ 6.236738] rcu_scheduler_active = 2, debug_locks = 1 >> [ 6.237039] no locks held by kunit_try_catch/208. >> [ 6.237166] >> [ 6.237166] stack backtrace: >> [ 6.237385] CPU: 0 UID: 0 PID: 208 Comm: kunit_try_catch Tainted: G N 6.11.0-rc6-00029-gda66250b210f-dirty #1 >> [ 6.237629] Tainted: [N]=TEST >> [ 6.237714] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 >> [ 6.238065] Call Trace: >> [ 6.238233] >> [ 6.238547] dump_stack_lvl+0x9e/0xe0 >> [ 6.239473] lockdep_rcu_suspicious+0x145/0x1b0 >> [ 6.239621] mas_walk+0x19f/0x1d0 >> [ 6.239765] mas_find+0xb5/0x150 >> [ 6.239873] __damon_va_three_regions+0x7e/0x130 > > This function isn't taking the rcu read lock while iterating the tree. > > Try this: > > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c > index b0e8b361891d..08cfd22b5249 100644 > --- a/mm/damon/vaddr.c > +++ b/mm/damon/vaddr.c > @@ -126,6 +126,7 @@ static int __damon_va_three_regions(struct mm_struct *mm, > * If this is too slow, it can be optimised to examine the maple > * tree gaps. > */ > + rcu_read_lock(); > for_each_vma(vmi, vma) { > unsigned long gap; > > @@ -146,6 +147,7 @@ static int __damon_va_three_regions(struct mm_struct *mm, > next: > prev = vma; > } > + rcu_read_unlock(); > > if (!sz_range(&second_gap) || !sz_range(&first_gap)) > return -EINVAL; > Yes, that fixes the problem for me. Thanks, Guenter