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[80.187.80.144]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fc5602dc2sm25902920f8f.32.2025.10.01.01.32.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 01 Oct 2025 01:32:04 -0700 (PDT) Message-ID: <819891f6-4e30-470c-b641-350a14b395a2@redhat.com> Date: Wed, 1 Oct 2025 10:32:02 +0200 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: [v2 PATCH] mm: hugetlb: avoid soft lockup when mprotect to large memory area To: Dev Jain , Yang Shi , muchun.song@linux.dev, osalvador@suse.de, akpm@linux-foundation.org, catalin.marinas@arm.com, will@kernel.org, anshuman.khandual@arm.com, carl@os.amperecomputing.com, cl@gentwo.org Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20250929202402.1663290-1-yang@os.amperecomputing.com> <6cde8290-3aa2-411c-bf29-eb91a99e33a5@os.amperecomputing.com> <746c4dd3-2285-4353-9e15-a0a2fbd4e6b5@arm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <746c4dd3-2285-4353-9e15-a0a2fbd4e6b5@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 01.10.25 06:23, Dev Jain wrote: > > On 30/09/25 11:38 pm, Yang Shi wrote: >> >> >> On 9/29/25 10:26 PM, Dev Jain wrote: >>> >>> On 30/09/25 1:54 am, Yang Shi wrote: >>>> When calling mprotect() to a large hugetlb memory area in our >>>> customer's >>>> workload (~300GB hugetlb memory), soft lockup was observed: >>>> >>>> watchdog: BUG: soft lockup - CPU#98 stuck for 23s! [t2_new_sysv:126916] >>>> >>>> CPU: 98 PID: 126916 Comm: t2_new_sysv Kdump: loaded Not tainted >>>> 6.17-rc7 >>>> Hardware name: GIGACOMPUTING R2A3-T40-AAV1/Jefferson CIO, BIOS >>>> 5.4.4.1 07/15/2025 >>>> pstate: 20400009 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) >>>> pc : mte_clear_page_tags+0x14/0x24 >>>> lr : mte_sync_tags+0x1c0/0x240 >>>> sp : ffff80003150bb80 >>>> x29: ffff80003150bb80 x28: ffff00739e9705a8 x27: 0000ffd2d6a00000 >>>> x26: 0000ff8e4bc00000 x25: 00e80046cde00f45 x24: 0000000000022458 >>>> x23: 0000000000000000 x22: 0000000000000004 x21: 000000011b380000 >>>> x20: ffff000000000000 x19: 000000011b379f40 x18: 0000000000000000 >>>> x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 >>>> x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 >>>> x11: 0000000000000000 x10: 0000000000000000 x9 : ffffc875e0aa5e2c >>>> x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000 >>>> x5 : fffffc01ce7a5c00 x4 : 00000000046cde00 x3 : fffffc0000000000 >>>> x2 : 0000000000000004 x1 : 0000000000000040 x0 : ffff0046cde7c000 >>>> >>>> Call trace: >>>>    mte_clear_page_tags+0x14/0x24 >>>>    set_huge_pte_at+0x25c/0x280 >>>>    hugetlb_change_protection+0x220/0x430 >>>>    change_protection+0x5c/0x8c >>>>    mprotect_fixup+0x10c/0x294 >>>>    do_mprotect_pkey.constprop.0+0x2e0/0x3d4 >>>>    __arm64_sys_mprotect+0x24/0x44 >>>>    invoke_syscall+0x50/0x160 >>>>    el0_svc_common+0x48/0x144 >>>>    do_el0_svc+0x30/0xe0 >>>>    el0_svc+0x30/0xf0 >>>>    el0t_64_sync_handler+0xc4/0x148 >>>>    el0t_64_sync+0x1a4/0x1a8 >>>> >>>> Soft lockup is not triggered with THP or base page because there is >>>> cond_resched() called for each PMD size. >>>> >>>> Although the soft lockup was triggered by MTE, it should be not MTE >>>> specific. The other processing which takes long time in the loop may >>>> trigger soft lockup too. >>>> >>>> So add cond_resched() for hugetlb to avoid soft lockup. >>>> >>>> Fixes: 8f860591ffb2 ("[PATCH] Enable mprotect on huge pages") >>>> Tested-by: Carl Worth >>>> Reviewed-by: Christoph Lameter (Ampere) >>>> Reviewed-by: Catalin Marinas >>>> Acked-by: David Hildenbrand >>>> Acked-by: Oscar Salvador >>>> Reviewed-by: Anshuman Khandual >>>> Signed-off-by: Yang Shi >>>> --- >>>> v2: - Made the subject and commit message less MTE specific and fixed >>>>        the fixes tag. >>>>      - Collected all R-bs and A-bs. >>>> >>>>   mm/hugetlb.c | 2 ++ >>>>   1 file changed, 2 insertions(+) >>>> >>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>> index cb5c4e79e0b8..fe6606d91b31 100644 >>>> --- a/mm/hugetlb.c >>>> +++ b/mm/hugetlb.c >>>> @@ -7242,6 +7242,8 @@ long hugetlb_change_protection(struct >>>> vm_area_struct *vma, >>>>                           psize); >>>>           } >>>>           spin_unlock(ptl); >>>> + >>>> +        cond_resched(); >>>>       } >>>>       /* >>>>        * Must flush TLB before releasing i_mmap_rwsem: x86's >>>> huge_pmd_unshare >>> >>> Reviewed-by: Dev Jain >> >> Thank you. >> >>> >>> Does it make sense to also do cond_resched() in the >>> huge_pmd_unshare() branch? >>> That also amounts to clearing a page. And I can see for example, >>> zap_huge_pmd() >>> and change_huge_pmd() consume a cond_resched(). >> >> Thanks for raising this. I did think about it. But I didn't convince >> myself because shared pmd should be not that common IMHO (If I'm >> wrong, please feel free to correct me). At least PMD can't be shared >> if the memory is tagged IIRC. So I'd like to keep the patch minimal >> for now and defer adding cond_resched() until it is hit by some real >> life workload. > > If we have large swathes of hugetlb memory like in your workload, and it > is MAP_SHARED, then there should be high chances of sharing the PMD. > Although, I incorrectly > > observed that we are clearing a page there - we are only clearing the > pud entry which is 8 bytes. So yes a soft lockup should be highly > unlikely. But since cond_resched() > > is cheap (I assume this is the case since it is liberally sprinkled all > over the codebase) I think we should be consistent. Probably not an > immediate concern and not a matter Right, that's one of the cases where we might just want to wait either until is is reported or until hugetlb is finally removed in a couple of decades ;) -- Cheers David / dhildenb