From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 A214C236956; Thu, 12 Dec 2024 16:45:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734021957; cv=none; b=JfBDOEORxb13Ga5+S/Kv3R4Y80a7wUxoMJL85R96YKdJntWwDgTEZ3p72aKDPsp4o4EvTcuTYlB30+mTnO6uFPOxd7+5jm61JAfXvv88jHwdUBJMrhRzt5Kzbhcws+R9jcEcMUhxZVrN+m33IprV1fbL7p3J+CXUV4YlqY4cxQE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734021957; c=relaxed/simple; bh=HtkS0L2/SwsThCB3AmVifn6oyEvG/GnWNl3lktsYhBw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OHQmZiKTlNA3vJm11q7WkhCx6B4oyVDJeYpYWxSnj7c6KkiUWBRErJcUKtsnGH72LCD2HJa9fbuqyeSyGjPu6nPebdMJzBPFPxkRcWiJZSWOTYmRdtVdHch9DwgF62kmp9zwq2YBSHA0Y6vHADyqb3dYdgx/k2hcC1kHg3XXYeQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=JDYEsxy1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="JDYEsxy1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECD1DC4CED0; Thu, 12 Dec 2024 16:45:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1734021957; bh=HtkS0L2/SwsThCB3AmVifn6oyEvG/GnWNl3lktsYhBw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JDYEsxy1NOwsb8dbvcuxu12+aSwu7F8jo3uvvh5xlnMJpgAtIdQkS4X8/QB3bUrhr A6v21piBzfDK7/TfRlUYKDXK0bEl2oS1SdQdgwqY3JidAvw8xeTRHBojYapVfGeSfB 815ZDEuS+3NHk1diqrZhphtZREdr0qncfIyIEmPI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Marco Elver , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 5.15 108/565] kcsan, seqlock: Fix incorrect assumption in read_seqbegin() Date: Thu, 12 Dec 2024 15:55:03 +0100 Message-ID: <20241212144315.744936114@linuxfoundation.org> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20241212144311.432886635@linuxfoundation.org> References: <20241212144311.432886635@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Marco Elver [ Upstream commit 183ec5f26b2fc97a4a9871865bfe9b33c41fddb2 ] During testing of the preceding changes, I noticed that in some cases, current->kcsan_ctx.in_flat_atomic remained true until task exit. This is obviously wrong, because _all_ accesses for the given task will be treated as atomic, resulting in false negatives i.e. missed data races. Debugging led to fs/dcache.c, where we can see this usage of seqlock: struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name) { struct dentry *dentry; unsigned seq; do { seq = read_seqbegin(&rename_lock); dentry = __d_lookup(parent, name); if (dentry) break; } while (read_seqretry(&rename_lock, seq)); [...] As can be seen, read_seqretry() is never called if dentry != NULL; consequently, current->kcsan_ctx.in_flat_atomic will never be reset to false by read_seqretry(). Give up on the wrong assumption of "assume closing read_seqretry()", and rely on the already-present annotations in read_seqcount_begin/retry(). Fixes: 88ecd153be95 ("seqlock, kcsan: Add annotations for KCSAN") Signed-off-by: Marco Elver Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20241104161910.780003-6-elver@google.com Signed-off-by: Sasha Levin --- include/linux/seqlock.h | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-) diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index a06af404c4b2a..49943cad85fe7 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -894,11 +894,7 @@ typedef struct { */ static inline unsigned read_seqbegin(const seqlock_t *sl) { - unsigned ret = read_seqcount_begin(&sl->seqcount); - - kcsan_atomic_next(0); /* non-raw usage, assume closing read_seqretry() */ - kcsan_flat_atomic_begin(); - return ret; + return read_seqcount_begin(&sl->seqcount); } /** @@ -914,12 +910,6 @@ static inline unsigned read_seqbegin(const seqlock_t *sl) */ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start) { - /* - * Assume not nested: read_seqretry() may be called multiple times when - * completing read critical section. - */ - kcsan_flat_atomic_end(); - return read_seqcount_retry(&sl->seqcount, start); } -- 2.43.0