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([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-206aea52a21sm4365605ad.196.2024.09.03.19.38.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Sep 2024 19:38:40 -0700 (PDT) Sender: Guenter Roeck Message-ID: Date: Tue, 3 Sep 2024 19:38:39 -0700 Precedence: bulk X-Mailing-List: linux-kernel@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> 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 9/3/24 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. Guenter >> >> ``` >> --- a/mm/damon/tests/vaddr-kunit.h >> +++ b/mm/damon/tests/vaddr-kunit.h >> @@ -77,7 +77,7 @@ static void damon_test_three_regions_in_vmas(struct kunit *test) >> (struct vm_area_struct) {.vm_start = 307, .vm_end = 330}, >> }; >> >> - mt_init_flags(&mm.mm_mt, MM_MT_FLAGS); >> + mt_init(&mm.mm_mt); >> if (__link_vmas(&mm.mm_mt, vmas, ARRAY_SIZE(vmas))) >> kunit_skip(test, "Failed to create VMA tree"); >> ``` >> >> And just confirmed it also convinces the reproducer. But because I'm obviously >> not familiar with maple tree, would like to hear some comments from Liam or >> others first. >> >> FYI, I ended up writing v1 to simply remove lock usage based on my humble >> understanding of the documetnation. >> >> The maple tree uses a spinlock by default, but external locks can be used for >> tree updates as well. To use an external lock, the tree must be initialized >> with the ``MT_FLAGS_LOCK_EXTERN flag``, this is usually done with the >> MTREE_INIT_EXT() #define, which takes an external lock as an argument. >> >> (from Documentation/core-api/maple_tree.rst) >> >> I was thinking the fact that the test code is executed in single thread is same >> to use of external lock. I will be happy to learn if I missed something. >> >> >> Thanks, >> SJ >> >>> >>> >>> Thanks, >>> SJ >>> >>>> >>>>> >>>>> Reported-by: Guenter Roeck >>>>> Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net >>>>> Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator") >>>>> Signed-off-by: SeongJae Park >>>>> --- >>>>> mm/damon/tests/vaddr-kunit.h | 10 +++------- >>>>> 1 file changed, 3 insertions(+), 7 deletions(-) >>>>> >>>>> diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h >>>>> index 83626483f82b..c6c7e0e0ab07 100644 >>>>> --- a/mm/damon/tests/vaddr-kunit.h >>>>> +++ b/mm/damon/tests/vaddr-kunit.h >>>>> @@ -17,23 +17,19 @@ >>>>> static int __link_vmas(struct maple_tree *mt, struct vm_area_struct *vmas, >>>>> ssize_t nr_vmas) >>>>> { >>>>> - int i, ret = -ENOMEM; >>>>> + int i; >>>>> MA_STATE(mas, mt, 0, 0); >>>>> >>>>> if (!nr_vmas) >>>>> return 0; >>>>> >>>>> - mas_lock(&mas); >>>>> for (i = 0; i < nr_vmas; i++) { >>>>> mas_set_range(&mas, vmas[i].vm_start, vmas[i].vm_end - 1); >>>>> if (mas_store_gfp(&mas, &vmas[i], GFP_KERNEL)) >>>>> - goto failed; >>>>> + return -ENOMEM; >>>>> } >>>>> >>>>> - ret = 0; >>>>> -failed: >>>>> - mas_unlock(&mas); >>>>> - return ret; >>>>> + return 0; >>>>> } >>>>> >>>>> /* >>>>> -- >>>>> 2.39.2 >>>>>