From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) (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 E66E91FF1DA for ; Tue, 21 Jul 2026 04:09:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784606985; cv=none; b=XdQwNFzoWJ9GicUeIKu6JEeNid1UyNpQlgjbdHXG1VvltMPvkTx+p07wz08cl/ubkwkohbrNvWkVhU8PvLJ416JHgnhx4dhIx+XbgzSFd+R+gj4Rs/u+kX6W3PohEcqPIAXENbzDLIkELT2iMUq274iG4FzhCRPUZo716WdY4bU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784606985; c=relaxed/simple; bh=TfHtN98F+C0beBAmQC91Qi2Fba7QSVBUL1zD90xob5U=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=VfururtGR6DkHEO5FKkMDb71/+XzdsWp/F7qkZrIL0Oc4WZunsx8s/5Ozc81XJnyHBBFy4EXAjAAH2ad7/bH+O8NRH/TijZSsCW5nXTMbm4vBQBHaVGQUwAnhx1zMMS7hbt4v/RgH/yZDc5vYA1Ve76bHP/v9In3xENrTA+AByg= 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=Q2fj3TUk; arc=none smtp.client-ip=95.215.58.187 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="Q2fj3TUk" 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=1784606967; 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=7RH3/Rwf7tA6LTcRQBD8dH2kVM7pDy1c+3FZ4K3r3vw=; b=Q2fj3TUkPE4a7UUD0FDxuB0mPANlCCFPRs6iya5K+S6c7MHuupWk1N97IZFYsnzY5xJagW Il/S8t37gTok+qjPZA/KAME8dj/nUmLsuMmHs71Y+AaJ3ho31IZi/3PuJ6X26Rkbav+h45 HAUAnWppWVE6ykUj+Htb/QF7WaGIJhw= From: Tao Cui To: tj@kernel.org, axboe@kernel.dk Cc: linux-block@vger.kernel.org, josef@toxicpanda.com, yukuai3@huawei.com, 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 v3] blk-throttle: fix divide-by-zero on legacy iops limit of 0 Date: Tue, 21 Jul 2026 12:08:50 +0800 Message-ID: <20260721040850.90544-1-cui.tao@linux.dev> Precedence: bulk X-Mailing-List: cgroups@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. The unclamped write in tg_set_conf() is long-standing, but it only became a crash once the HZ / iops_limit divide was added. Fix it in two places: * tg_set_conf(): clamp the value to UINT_MAX, consistent with tg_set_limit(). This closes the truncation root cause (and the general silent truncation for any value above UINT_MAX). * tg_dispatch_iops_time(): treat iops_limit == 0 as unlimited so the divide in tg_within_iops_limit() is never reached, defending against any future path that could produce a zero limit. Fixes: 1beabab88ece ("blk-throttle: fix lower control under super low iops limit") Signed-off-by: Tao Cui --- 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) - Add a Fixes: tag pointing at the commit that introduced the HZ / iops_limit divide, which is also where the oops became reachable. 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 | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index ffc3b70065d4..e894852c3142 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -883,7 +883,12 @@ static unsigned long tg_dispatch_iops_time(struct throtl_grp *tg, struct bio *bi u32 iops_limit = tg_iops_limit(tg, rw); unsigned long iops_wait; - if (iops_limit == UINT_MAX || tg->flags & THROTL_TG_CANCELING) + /* + * iops_limit == 0 is not a valid limit. Treat it as unlimited so we + * never reach the HZ / iops_limit divide in tg_within_iops_limit(). + */ + if (iops_limit == UINT_MAX || iops_limit == 0 || + tg->flags & THROTL_TG_CANCELING) return 0; tg_update_slice(tg, rw); @@ -1383,10 +1388,12 @@ 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