From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 31B9D14A8B for ; Thu, 4 Apr 2024 17:21:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712251315; cv=none; b=nyPdSwJTXYuLN2oUrnqKzsa9kjbURyAxRKcI9dzEYBTBbVtf7ucXSoY3VRwmisWo5lvkcfCXHCLC0TdJ022i1b1EOq0RoWpbcq5nghE5tivL2SULLjTML6WGjNhP98iMnH+YsIdnbBMzAKmBKGovAIQnBp0AV0fxy3Pylpzb1do= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712251315; c=relaxed/simple; bh=I/Y7BkE/ovvkHXAQwnA3lR9TA6Ahb13PwB8H9hTUXKY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jPnHwZFnLDotz3UsdcK33M8oMzhtZwnqGtQGNB8cmk5Q8ylpODIDtB0QvUiii1tImjGu9JujGtsKWGfwYGTWXlDN9Nviwq7VVPAIJJ0/9YY6LZQLE429XXYL2oq+lwZbhpu1DPPzFAzVUsmwndFQO38B56hcr2BmD/QWKlTzkwI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=HAhC2m7Z; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="HAhC2m7Z" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=2AAEG8ys83OU4EuRCbJQyodfMWerUNVMHCfTJ2nvxPU=; b=HAhC2m7ZVzD6zPrXiQJLgjLHaW AO3AVTmlWvFBXCD1yKqq7bWONdClkxDKKJ3ou7VzLfGQ/SMxwkrdwQqdaZQAlCW1NbH0geh5Jid2q 9AAaaRG/qZaJvCcgYoNWMcAgIXza61/yE3cZ/QBg0Wxsvzg5hrrq9waG574EojwJgRNGAp6yrHLrA xwXaqqkcWFNBIABKNY7wzOXtPho8VvFFLo+wkpM8JbBkVGaPIbBs298IlNWBXmC5qoNiLkBaeE8c7 +1o3MRkpK6xiKTBkPvFLTjVOE9SGQhc2JGcEPImDkJFyBRKoLIgobIMBAGJ4QbwPF321JJtG1x7/J HhzVRtHQ==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rsQmc-00000008WpL-1PQc; Thu, 04 Apr 2024 17:21:50 +0000 Date: Thu, 4 Apr 2024 18:21:50 +0100 From: Matthew Wilcox To: Lokesh Gidra Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, surenb@google.com, kernel-team@android.com, aarcange@redhat.com, peterx@redhat.com, david@redhat.com, zhengqi.arch@bytedance.com, kaleshsingh@google.com, ngeoffray@google.com Subject: Re: [PATCH] userfaultfd: change src_folio after ensuring it's unpinned in UFFDIO_MOVE Message-ID: References: <20240404171726.2302435-1-lokeshgidra@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240404171726.2302435-1-lokeshgidra@google.com> On Thu, Apr 04, 2024 at 10:17:26AM -0700, Lokesh Gidra wrote: > - folio_move_anon_rmap(src_folio, dst_vma); > - WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr)); > - > src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd); > /* Folio got pinned from under us. Put it back and fail the move. */ > if (folio_maybe_dma_pinned(src_folio)) { > @@ -2270,6 +2267,9 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm > goto unlock_ptls; > } > > + folio_move_anon_rmap(src_folio, dst_vma); > + WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr)); > + This use of WRITE_ONCE scares me. We hold the folio locked. Why do we need to use WRITE_ONCE? Who's looking at folio->index without holding the folio lock?