Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 85E58C05027 for ; Fri, 10 Feb 2023 21:19:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233832AbjBJVTB (ORCPT ); Fri, 10 Feb 2023 16:19:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40998 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232950AbjBJVSz (ORCPT ); Fri, 10 Feb 2023 16:18:55 -0500 Received: from out-191.mta1.migadu.com (out-191.mta1.migadu.com [IPv6:2001:41d0:203:375::bf]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0F7E81CC6 for ; Fri, 10 Feb 2023 13:18:26 -0800 (PST) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1676063899; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Qnr9u9smPMPXsKAXlYWG4fUkkGTB3Zxw4vbQvgaYcVg=; b=t7vDpQcZUJdsleERJ1PgO38Pvi8xFhTNn74zLonJYcITtx61e02XeD2vPBg9c//+BpeG1V s7T+qicncVYyTp2KtBAyctdyaGSJ7zdRMIgR7n9TfK44wSuf3yHrV92DaF9e4tXpgOOkwx I+Gi5V7tNQW76e1Nfyz/DJq/+nVFLGI= From: andrey.konovalov@linux.dev To: Marco Elver , Alexander Potapenko Cc: Andrey Konovalov , Vlastimil Babka , kasan-dev@googlegroups.com, Evgenii Stepanov , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov Subject: [PATCH v2 16/18] lib/stackdepot: annotate racy pool_index accesses Date: Fri, 10 Feb 2023 22:16:04 +0100 Message-Id: <359ac9c13cd0869c56740fb2029f505e41593830.1676063693.git.andreyknvl@google.com> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andrey Konovalov Accesses to pool_index are protected by pool_lock everywhere except in a sanity check in stack_depot_fetch. The read access there can race with the write access in depot_alloc_stack. Use WRITE/READ_ONCE() to annotate the racy accesses. As the sanity check is only used to print a warning in case of a violation of the stack depot interface usage, it does not make a lot of sense to use proper synchronization. Signed-off-by: Andrey Konovalov --- Changes v1->v2: - Improve comments as suggested by Marco. --- lib/stackdepot.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 8c6e4e9cb535..684c2168bed9 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -278,8 +278,12 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc) return NULL; } - /* Move on to the next pool. */ - pool_index++; + /* + * Move on to the next pool. + * WRITE_ONCE pairs with potential concurrent read in + * stack_depot_fetch(). + */ + WRITE_ONCE(pool_index, pool_index + 1); pool_offset = 0; /* * If the maximum number of pools is not reached, take note @@ -502,6 +506,11 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle, unsigned long **entries) { union handle_parts parts = { .handle = handle }; + /* + * READ_ONCE pairs with potential concurrent write in + * depot_alloc_stack. + */ + int pool_index_cached = READ_ONCE(pool_index); void *pool; size_t offset = parts.offset << DEPOT_STACK_ALIGN; struct stack_record *stack; @@ -510,7 +519,7 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle, if (!handle) return 0; - if (parts.pool_index > pool_index) { + if (parts.pool_index > pool_index_cached) { WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n", parts.pool_index, pool_index, handle); return 0; -- 2.25.1