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De Francesco" , lkp@lists.01.org, lkp@intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Peter Xu , Andrea Arcangeli References: <202210211215.9dc6efb5-yujie.liu@intel.com> <20221021133041.5811e1fb291eb6aaf122a59c@linux-foundation.org> From: Randy Dunlap In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b="P/YCZyVR"; spf=none (imf02.hostedemail.com: domain of rdunlap@infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=rdunlap@infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666396994; a=rsa-sha256; cv=none; b=X7E6IjQ0xWoonh2eszi3BpGl1ULxafYg8V2bJjM/Z5rUQySINGSbCGXDBFUu3q3r9XAGQE zkt/w9Gm2+HAccBQt6X+boF8fJ+A4aER8a1xeISHEt2e+Se0lhlzVVtNq4CLNURFH10/Fu 2tgaGE5fnzqYhlSt5Ujx6BX4oHTqcOk= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666396994; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=FsbSvlVxGH7D4k107lqA7eAi/c6cWz3yuiU0rZC9C0c=; b=HjY5MHuHEEAWDUa3lQV0fur/S78stCqhbwWOlO3oJM+ac8vRs+09VmFDTbeGIlV//6J7b4 JIli7ARAoPmRQsebPUtoJCqxnoogb2AZlEwVb5hEOWJmkAFMOLODzoAO39jNGiRvso8eJt PazHllcKgtVd5lWr2/1IbE18Ep31gkk= Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b="P/YCZyVR"; spf=none (imf02.hostedemail.com: domain of rdunlap@infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=rdunlap@infradead.org; dmarc=none X-Rspam-User: X-Rspamd-Server: rspam10 X-Stat-Signature: kz5ywuzfc7epgzrtudfwso37ds5epa1k X-Rspamd-Queue-Id: 8BE1980003 X-HE-Tag: 1666396993-644856 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 10/21/22 17:00, Ira Weiny wrote: > > I was about to get this patch ready to send when I found this: > > commit b6ebaedb4cb1a18220ae626c3a9e184ee39dd248 > Author: Andrea Arcangeli > Date: Fri Sep 4 15:47:08 2015 -0700 > > userfaultfd: avoid mmap_sem read recursion in mcopy_atomic > > If the rwsem starves writers it wasn't strictly a bug but lockdep > doesn't like it and this avoids depending on lowlevel implementation > details of the lock. > > [akpm@linux-foundation.org: delete weird BUILD_BUG_ON()] > Signed-off-by: Andrea Arcangeli > Acked-by: Pavel Emelyanov > ... > > So I wonder if the true fix is something to lockdep? > > Regardless I'll send the below patch because it will restore things to a > working order. with ; added to each + line. > But I'm CC'ing Andrea for comments. > > Ira > >> >> Ira >> >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 8280a5cb48df..6c8e99bf5983 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -2424,9 +2424,11 @@ int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, >> >> if (!zeropage) { /* COPY */ >> page_kaddr = kmap_local_folio(folio, 0); >> + pagefault_disable() >> ret = copy_from_user(page_kaddr, >> (const void __user *)src_addr, >> PAGE_SIZE); >> + pagefault_enable() >> kunmap_local(page_kaddr); >> >> /* fallback to copy_from_user outside mmap_lock */ >> >> -- ~Randy