From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-185.mta0.migadu.com (out-185.mta0.migadu.com [91.218.175.185]) (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 59EDD339371; Wed, 22 Jul 2026 10:25:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.185 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784715924; cv=none; b=ckc47spqoTqwAKLU6Yv8VB96RPGdt7B5GZYdfexxSIvsCGeC15VuSJjwLN+TqBq4+e1dOWIc8ilxtLzC951rQRk52RUGpAd+U9manZ7aEV4XJvteBP4gQTAeTPEuIT1EwDmxwXamMA5uwiwxsHej0EiN26DaNajvziWB1zhXc3A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784715924; c=relaxed/simple; bh=1OcsFA5xETydKj/a/BPRbzK34nAsDcbpJ4tIWjpAfgQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=CFnFU/iRbV7p78DZ7bTXryws4sYJ0gTbXaCW+vZMHAFGD7kUBvlbfM6etxu3mBbkoFJJqsJfJiXAVZFITLOEgGbv6AMSW8iMFwa8///KDEMANEQKirzmgG6NHG9ITUcKNJYHkHup3an/duOoah0+A9IxddkJSEvBDZnwU6S3ZyQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=JmGuYE6+; arc=none smtp.client-ip=91.218.175.185 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="JmGuYE6+" 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=1784715910; 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; bh=gi0rqPlLMNHpvuGTqnaQG76LXt2I74tCCqNp3y8hndw=; b=JmGuYE6+CypZ8sKIfnhZ1RpivPmM3nHfhU1gFdVpdotYJKRZQIOO4g7n3Bk9pzBEWszVtY ecTENsnbgkLi04GGuwWXEkYjKasLRexpCdQyGuM6qRyqid01gkgDSgSuoJu6Yw3Ypn7n6m WQtGf1M50lqPoBc5Wek8cH8ubeKiJyA= From: Tao Cui To: tj@kernel.org, axboe@kernel.dk Cc: linux-block@vger.kernel.org, josef@toxicpanda.com, yu kuai , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, david.laight.linux@gmail.com, haris.iqbal@linux.dev, cui.tao@linux.dev, Tao Cui Subject: [PATCH v4] blk-throttle: fix divide-by-zero on legacy iops limit of 0 Date: Wed, 22 Jul 2026 18:24:59 +0800 Message-ID: <20260722102459.253189-1-cui.tao@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Tao Cui Writing a multiple of 2^32 (e.g. 4294967296) to a legacy cgroup v1 throttle iops file (blkio.throttle.{read,write}_iops_device) silently truncates to 0: tg_set_conf() stores the sscanf-parsed u64 value into an unsigned int field with no clamping. The cgroup v2 path, tg_set_limit(), already clamps the same kind of value with min_t(u64, val, UINT_MAX), but the legacy path never did. Note that the "!v -> U64_MAX" mapping only catches an explicit zero and does not catch a value that truncates to zero. With iops stored as 0, tg_update_has_rules() sets has_rules_iops[] and the next IO reaches tg_within_iops_limit(), which computes jiffy_wait = max(jiffy_wait, HZ / iops_limit + 1); triggering a divide-by-zero oops. Fix it in tg_set_conf() by clamping the value to UINT_MAX, consistent with tg_set_limit(). This closes the truncation root cause: with 0 no longer reachable as a stored limit, the HZ / iops_limit divide is never hit. Signed-off-by: Tao Cui --- Changes in v4: - Drop the defensive "iops_limit == 0" check in tg_dispatch_iops_time(): with the tg_set_conf() clamp in place, 0 can never be stored as a limit, so the runtime check only guards an unreachable state. (Yu Kuai) - Drop the Fixes: tag: the unclamped write -- and the iops=0 behavior it can produce (calculate_io_allowed() returns 0, so no IO is issued) -- long predates the commit that added the HZ / iops_limit divide, so attributing it there was incorrect. (Yu Kuai) Changes in v3: - Drop the (u64) cast on UINT_MAX: the kernel's type-checked min() accepts two unsigned types of different width (both >= 4 bytes), so min(v, UINT_MAX) compiles clean. (David Laight) Changes in v2: - Use a "void *field" local for the config write so the assignment reads *(u64 *)field / *(unsigned int *)field instead of the (type *)((void *)tg + of_cft(of)->private) casts. - Use min(v, UINT_MAX) instead of min_t(u64, v, UINT_MAX). --- block/blk-throttle.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index ffc3b70065d4..97ad7959d006 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -1383,10 +1383,12 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of, tg = blkg_to_tg(ctx.blkg); tg_update_carryover(tg); + void *field = (void *)tg + of_cft(of)->private; + if (is_u64) - *(u64 *)((void *)tg + of_cft(of)->private) = v; + *(u64 *)field = v; else - *(unsigned int *)((void *)tg + of_cft(of)->private) = v; + *(unsigned int *)field = min(v, UINT_MAX); tg_conf_updated(tg, false); ret = 0; -- 2.43.0