From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E76F22D8DDF; Mon, 17 Aug 2026 14:02:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786975379; cv=none; b=RyTipWI23Koj6mxC+MKlI+tD547KTQPhlJJdsmYYQWunO54FQX2y5F7vkku28vVOxXct4T4S4O5vj+JBMdWIf6pWjXa0CVradmIT3iTJTcLWAPhAevVbGrHL1EbB5p2z20SbhAZPUMSDutGbpJXL7uoAOXEIb8O44FcI/jPCQkw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786975379; c=relaxed/simple; bh=5aWzV10u9isWyFqCwFLyTwC6TmVe4/i7NOIwJqkex8I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DioVfeg4bW4Fay+YrwKrLSYS45ZUzkjoaehURyzXAA6CqKyl6JplOJCU/qDgzf/wYOYbyAGl/BkZH03rEvRplsyydOmzpLnQ+OWQ1ia1jGcmhZX8xgSlXNAPCXvrOXbuoZ3LREepYkkWnKuwkfeRUFtOtr93qmbfYdmiIIFLVGg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=XkQphHhN; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="XkQphHhN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3D5671F000E9; Mon, 17 Aug 2026 14:02:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786975377; bh=0BpZet8IIt9bkQ8+qAoJ3zCcPmwCgjQG7HbwuNamwvk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=XkQphHhNahrtDMFT0DdxZfRdyEErMkrYlu7Pki2keNYk44Q0MhHDK6ILhofegGFje jMIzMpFCjQxYRAKaHCtHYt9CMl/ZiWyLs5YqEHoxSXU3GK3TXnViKz29Eg9aRzI/yn THSYaQlCUXOUhhKum4ZQ5pcSfbdny5ikD24W8wTg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Hugh Dickins , "Kiryl Shutsemau (Meta)" , "Matthew Wilcox (Oracle)" , Zi Yan , Chris J Arges , David Hildenbrand , Jan Kara , Kairui Song , Andrew Morton Subject: [PATCH 6.18 239/250] mm/filemap: __filemap_add_folio() restore index before retrying Date: Mon, 17 Aug 2026 15:33:20 +0200 Message-ID: <20260817132546.251337591@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260817132536.466235697@linuxfoundation.org> References: <20260817132536.466235697@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Hugh Dickins commit 86da3f7e1e609e1e8bfbab198af68467c5a015a5 upstream. In __filemap_add_folio()'s split-a-conflict loop, xas_set_order() is applied repeatedly: each application modifies xas.xa_index, rounding it down according to the split_order attempted at that stage: and if all goes as intended, it eventually (or immediately) converges on an xas_try_split() to the required folio_order, with xas.xa_index now the same as index: then xas_store() puts the new folio into the xarray there. But if a new node was needed, and GFP_NOWAIT allocation did not get one, the lock is dropped, xas_nomem() used to allocate, and sequence retried. If (that part of) the xarray is unchanged when the lock is reacquired, no problem. But what if the conflict was meanwhile resolved by another thread (perhaps even doing the same thing, inserting a folio at that same index)? Isn't there a danger of now putting our folio into the xarray at an intermediate rounded-down index? With !folio_contains() bug to follow, when CONFIG_DEBUG_VM=y is checking for that. Fix this with an xas_set_order() to restore the original xas.xa_index at the bottom of the loop, so the retry does a full re-evaluation after reacquiring the lock, and cannot reach xas_store() with the wrong index. Production was suffering from rare SIGILLs and SIGSEGVs, executable text found a page away from where it belonged, !folio_contains() bug hit when debug enabled: symptoms not seen since this patch went in. Link: https://lore.kernel.org/562fbfa6-dd6d-0b6a-2461-ed2ff1173bc8@google.com Fixes: 200a89c159a7 ("mm/filemap: use xas_try_split() in __filemap_add_folio()") Signed-off-by: Hugh Dickins Acked-by: Kiryl Shutsemau (Meta) Reviewed-by: Matthew Wilcox (Oracle) Reviewed-by: Zi Yan Cc: Chris J Arges Cc: David Hildenbrand Cc: Jan Kara Cc: Kairui Song Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/filemap.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -944,6 +944,12 @@ unlock: if (!xas_nomem(&xas, gfp)) break; + + /* + * Lock has been dropped: start again with the original index + * and order (but now with the memory reserved by xas_nomem()). + */ + xas_set_order(&xas, index, forder); } if (xas_error(&xas))