Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 216.228.112.34 as permitted sender) receiver=protection.outlook.com;
 client-ip=216.228.112.34; helo=mail.nvidia.com;
Subject: Re: [PATCH] mm: cma: fix corruption cma_sysfs_alloc_pages_count
To:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
CC:     linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        <gregkh@linuxfoundation.org>, <surenb@google.com>,
        <joaodias@google.com>, <willy@infradead.org>, <digetx@gmail.com>
References: <20210324192044.1505747-1-minchan@kernel.org>
From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <01e09f8b-93f9-cd59-1f12-7ab4c86743e6@nvidia.com>
Date:   Wed, 24 Mar 2021 12:45:17 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.8.1
MIME-Version: 1.0
In-Reply-To: <20210324192044.1505747-1-minchan@kernel.org>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Mar 2021 19:45:20.8693
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 7b4663da-eecb-4a44-aa2f-08d8eefd5bf4
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT023.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5238
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 3/24/21 12:20 PM, Minchan Kim wrote:
> struct cma_stat's lifespan for cma_sysfs is different with
> struct cma because kobject for sysfs requires dynamic object
> while CMA is static object[1]. When CMA is initialized,
> it couldn't use slab to allocate cma_stat since slab was not
> initialized yet. Thus, it allocates the dynamic object
> in subsys_initcall.
> 
> However, the cma allocation can happens before subsys_initcall
> then, it goes crash.
> 
> Dmitry reported[2]:
> 
> ..
> [    1.226190] [<c027762f>] (cma_sysfs_alloc_pages_count) from [<c027706f>] (cma_alloc+0x153/0x274)
> [    1.226720] [<c027706f>] (cma_alloc) from [<c01112ab>] (__alloc_from_contiguous+0x37/0x8c)
> [    1.227272] [<c01112ab>] (__alloc_from_contiguous) from [<c1104af9>] (atomic_pool_init+0x7b/0x126)
> [    1.233596] [<c1104af9>] (atomic_pool_init) from [<c0101d69>] (do_one_initcall+0x45/0x1e4)
> [    1.234188] [<c0101d69>] (do_one_initcall) from [<c1101141>] (kernel_init_freeable+0x157/0x1a6)
> [    1.234741] [<c1101141>] (kernel_init_freeable) from [<c0a27fd1>] (kernel_init+0xd/0xe0)
> [    1.235289] [<c0a27fd1>] (kernel_init) from [<c0100155>] (ret_from_fork+0x11/0x1c)
> 
> This patch moves those statistic fields of cma_stat into struct cma
> and introduces cma_kobject wrapper to follow kobject's rule.
> 
> At the same time, it fixes other routines based on suggestions[3][4].
> 
> [1] https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/
> [2] https://lore.kernel.org/linux-mm/fead70a2-4330-79ff-e79a-d8511eab1256@gmail.com/
> [3] https://lore.kernel.org/linux-mm/20210323195050.2577017-1-minchan@kernel.org/
> [4] https://lore.kernel.org/linux-mm/20210324010547.4134370-1-minchan@kernel.org/
> 
> Reported-by: Dmitry Osipenko <digetx@gmail.com>
> Tested-by: Dmitry Osipenko <digetx@gmail.com>
> Suggested-by: Dmitry Osipenko <digetx@gmail.com>
> Suggested-by: John Hubbard <jhubbard@nvidia.com>
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> I belive it's worth to have separate patch rather than replacing
> original patch. It will also help to merge without conflict
> since we already filed other patch based on it.
> Strictly speaking, separating fix part and readbility part
> in this patch would be better but it's gray to separate them
> since most code in this patch was done while we were fixing
> the bug. Since we don't release it yet, I hope it will work.
> Otherwise, I can send a replacement patch inclucing all of
> changes happend until now with gathering SoB.

If we still have a choice, we should not merge a patch that has a known
serious problem, such as a crash. That's only done if the broken problematic
patch has already been committed to a tree that doesn't allow rebasing,
such as of course the main linux.git.

Here, I *think* it's just in linux-next and mmotm, so we still are allowed
to fix the original patch.

thanks,
-- 
John Hubbard
NVIDIA