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Fri, 24 Mar 2023 09:05:33 -0400 (EDT) Received: by box.shutemov.name (Postfix, from userid 1000) id 0D6ED10A607; Fri, 24 Mar 2023 16:05:30 +0300 (+03) Date: Fri, 24 Mar 2023 16:05:30 +0300 From: "Kirill A. Shutemov" To: Michal Hocko Cc: Linus Torvalds , Naresh Kamboju , Joel Fernandes , Andrew Morton , linux-mm@kvack.org, LKML Subject: Re: WARN_ON in move_normal_pmd Message-ID: <20230324130530.xsmqcxapy4j2aaik@box.shutemov.name> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 82310A001D X-Rspam-User: X-Stat-Signature: y9jks1w6sj5bynfd5k8cpwf3ri6czfj6 X-HE-Tag: 1679663134-434033 X-HE-Meta: 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 RcV6YmFr RPLMjQBP/LvpAcdYIK6MjqoxGA1/++baHLtwObcPNNPc2IsrT7OLiOt/66YF8rwsm1xnl/lnWVZ+IAlP8RwFv9fSb28hcaDT7GCXg+miN7Y2IL44KPfB0wIJONARTJtUx2gkx2t/aXUGNQoNBAeoEMnjCD4xvrygQJW69W03n1tCecKkfji68sLRGgxC8dzq4z/mPn1Eo3mwkymfduLLLBWVV7sIe5I9kyMhAoHRziWGFx0AQ4veN/++nwzBDXYIp0MAt40vp1zMS7JYNYDEKe5N6MnB96k9i3lSjyA/w5vP4QzbqXch05jlq81E3J5SyExlwYoo5iZzqk0aUgHyiyMsuQIY822TaWulX X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Mar 24, 2023 at 12:15:24PM +0100, Michal Hocko wrote: > Hi, > our QA is regularly hitting > [ 544.198822][T20518] WARNING: CPU: 1 PID: 20518 at ../mm/mremap.c:255 move_pgt_entry+0x4c6/0x510 > triggered by thp01 LTP test. This has been brought up in the past and > resulted in f81fdd0c4ab7 ("mm: document warning in move_normal_pmd() and > make it warn only once"). While it is good that the underlying problem > is understood, it doesn't seem there is enough interest to fix it > properly. Which is fair but I am wondering whether the WARN_ON gives > us anything here. > > Our QA process collects all unexpected side effects of tests and a WARN* > in the log is certainly one of those. This trigger bugs which are mostly > ignored as there is no upstream fix for them. This alone is nothing > really critical but there are workloads which do run with panic on warn > configured and this issue would put the system down which is unnecessary > IMHO. Would it be sufficient to replace the WARN_ON_ONCE by > pr_warn_once? What about relaxing the check to exclude temporary stack from the WARN condition: diff --git a/mm/mremap.c b/mm/mremap.c index 411a85682b58..eb0778b9d645 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -247,15 +247,12 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr, * of any 4kB pages, but still there) PMD in the page table * tree. * - * Warn on it once - because we really should try to figure - * out how to do this better - but then say "I won't move - * this pmd". - * - * One alternative might be to just unmap the target pmd at - * this point, and verify that it really is empty. We'll see. + * Warn on it once unless it is initial (temporary) stack. */ - if (WARN_ON_ONCE(!pmd_none(*new_pmd))) + if (!pmd_none(*new_pmd)) { + WARN_ON_ONCE(!vma_is_temporary_stack(vma)); return false; + } /* * We don't have to worry about the ordering of src and dst -- Kiryl Shutsemau / Kirill A. Shutemov