From mboxrd@z Thu Jan 1 00:00:00 1970 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id BAE26C369D2 for ; Mon, 21 Apr 2025 07:09:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 681D76B0006; Mon, 21 Apr 2025 03:09:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5E3A06B0007; Mon, 21 Apr 2025 03:09:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 45EE96B0008; Mon, 21 Apr 2025 03:09:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 246626B0006 for ; Mon, 21 Apr 2025 03:09:09 -0400 (EDT) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id DA50A141A90 for ; Mon, 21 Apr 2025 07:09:09 +0000 (UTC) X-FDA: 83357174418.13.59413FC Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) by imf23.hostedemail.com (Postfix) with ESMTP id DFFB5140003 for ; Mon, 21 Apr 2025 07:09:04 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=none; spf=pass (imf23.hostedemail.com: domain of yukuai1@huaweicloud.com designates 45.249.212.51 as permitted sender) smtp.mailfrom=yukuai1@huaweicloud.com; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1745219348; a=rsa-sha256; cv=none; b=bQ8aBMc4Z3fyOujkDg/8hdZVvI1QPot3HIte6ktFmJqNJoq9+459r2JSY+HcTAQa4NUpVB JaeIpgpuAYk9fhFakpQlX0F8I5aV+P1101pZCy6tJ+wNdSVbAh1cZErGjMeU3s+8O8aU4v kAXVX41rZAwS4f4VOYT5IBN7i0J22bY= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=none; spf=pass (imf23.hostedemail.com: domain of yukuai1@huaweicloud.com designates 45.249.212.51 as permitted sender) smtp.mailfrom=yukuai1@huaweicloud.com; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1745219348; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yQ8oWv/vIq82IuFbaM5aJFiyTiFNHcH+5GAuttCvSX8=; b=z8RLStwgZCMdBOrFJyJotZ7qJcfyjGaapPTsc3IcdROMUMCEn/BN5Bkk0uQQZaV2TPElaV N5l5zu7OXkmuM+KlwB5ZGq4oUSreTj1IBUepAI0SnskoLfYxT32H6x8Ji/lxUwm38PlKe7 AjHvIr3vGXF8y+bA/1KkPQFaPCNEnLY= Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4ZgxL138Q6z4f3jtK for ; Mon, 21 Apr 2025 15:08:41 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 00F811A0359 for ; Mon, 21 Apr 2025 15:08:59 +0800 (CST) Received: from [10.174.179.143] (unknown [10.174.179.143]) by APP4 (Coremail) with SMTP id gCh0CgBXu18K7wVo9fl3KA--.2539S3; Mon, 21 Apr 2025 15:08:59 +0800 (CST) Subject: Re: [PATCH 2/5] brd: synchronize using page and free page with rcu To: Christoph Hellwig , Yu Kuai Cc: axboe@kernel.dk, kbusch@kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, yangerkun@huawei.com, johnny.chenyi@huawei.com, linux-mm@kvack.org, "yukuai (C)" References: <20250418093826.3149293-1-yukuai1@huaweicloud.com> <20250418093826.3149293-3-yukuai1@huaweicloud.com> From: Yu Kuai Message-ID: <8de49859-8441-ee02-6114-ec2c9f89ada1@huaweicloud.com> Date: Mon, 21 Apr 2025 15:08:57 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgBXu18K7wVo9fl3KA--.2539S3 X-Coremail-Antispam: 1UD129KBjvJXoWxXr43tw13XFyfCF1kWw48WFg_yoW5XFW7pF WUAFyxCrWDZr17K3WSq3Z0vryFq3s2qrWrGFWxG3yUK3sxCr9Fya48tw1rWF4rCrn5Gr42 vws0yryxZwn5A37anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUBF14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26F1j6w1UM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvEwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lFIxGxcIEc7CjxVA2Y2ka 0xkIwI1lc7I2V7IY0VAS07AlzVAYIcxG8wCY1x0262kKe7AKxVWUtVW8ZwCF04k20xvY0x 0EwIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E 7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_GFylIxkGc2Ij64vIr41lIxAIcV C0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_Gr0_Cr1lIxAIcVCF 04k26cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2jsIEc7 CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x0JUd-B_UUUUU= X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ X-Rspamd-Queue-Id: DFFB5140003 X-Stat-Signature: mnnp3c7e7hnqghzynkic6drra9qx87sm X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1745219344-40444 X-HE-Meta: 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 QCKDu6hv KLL4C2PFQ3bczqv5kCz69/lFUscLHari1EFJ1gnNyDGS+2TzRaBFMnNPnUZdytk6EWmylGUDgyTYtrx5u5ThPNaZ+QBgyNCNxzFbrlZ0HM0BwrIoiQPxoUwI/JkidpdQbpx/tonmCLA2ugSgvPrkfbTlQNfNLTrPPpiGRxe/FZ24IL6I= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, ÔÚ 2025/04/21 13:24, Christoph Hellwig дµÀ: > On Fri, Apr 18, 2025 at 05:38:23PM +0800, Yu Kuai wrote: >> From: Yu Kuai >> >> Currently, after fetching the page by xa_load() in IO path, there is no >> protection and page can be freed concurrently by discard: > > Ah, I guess this helps with the race I mentioned in reply to the > previous patch. Is the rcu_head in struct page available for use > by subsystems freeing the page? Take a look at other union fileds int the struct page, in this case, the page: - not used for pagecache or anonymous page - not used for page_pool - not used for compound page - not used for zone device page So, I think it's fine to use the rcu_head. We may want to avoid the page reference here since it's atomic and will affect IO performance. BTW, perhaps this patch should be the first patch in this set. :) Thanks, Kuai > >> >> cpu0 >> brd_submit_bio >> brd_do_bvec >> page = brd_lookup_page >> cpu1 >> brd_submit_bio >> brd_do_discard >> page = __xa_erase() >> __free_page() >> // page UAF >> >> Fix the problem by protecting page with rcu. >> >> Fixes: 9ead7efc6f3f ("brd: implement discard support") >> Signed-off-by: Yu Kuai >> --- >> drivers/block/brd.c | 11 ++++++++++- >> 1 file changed, 10 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/block/brd.c b/drivers/block/brd.c >> index a6e4f005cb76..740ed13faaff 100644 >> --- a/drivers/block/brd.c >> +++ b/drivers/block/brd.c >> @@ -208,6 +208,7 @@ static int brd_do_bvec(struct brd_device *brd, struct page *page, >> goto out; >> } >> >> + rcu_read_lock(); >> mem = kmap_local_page(page); >> if (!op_is_write(opf)) { >> copy_from_brd(mem + off, brd, sector, len); >> @@ -217,11 +218,19 @@ static int brd_do_bvec(struct brd_device *brd, struct page *page, >> copy_to_brd(brd, mem + off, sector, len); >> } >> kunmap_local(mem); >> + rcu_read_unlock(); >> >> out: >> return err; >> } >> >> +static void brd_free_one_page(struct rcu_head *head) >> +{ >> + struct page *page = container_of(head, struct page, rcu_head); >> + >> + __free_page(page); >> +} >> + >> static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size) >> { >> sector_t aligned_sector = (sector + PAGE_SECTORS) & ~PAGE_SECTORS; >> @@ -232,7 +241,7 @@ static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size) >> while (size >= PAGE_SIZE && aligned_sector < rd_size * 2) { >> page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT); >> if (page) { >> - __free_page(page); >> + call_rcu(&page->rcu_head, brd_free_one_page); >> brd->brd_nr_pages--; >> } >> aligned_sector += PAGE_SECTORS; >> -- >> 2.39.2 >> >> > ---end quoted text--- > > . >