linux-kernel - Re: [PATCH] mm: cma: fix corruption cma_sysfs_alloc_pages

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Date:   Wed, 24 Mar 2021 20:53:26 +0100
From:   David Hildenbrand <david@...hat.com>
To:     John Hubbard <jhubbard@...dia.com>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        gregkh@...uxfoundation.org, surenb@...gle.com, joaodias@...gle.com,
        willy@...radead.org, digetx@...il.com
Subject: Re: [PATCH] mm: cma: fix corruption cma_sysfs_alloc_pages_count

On 24.03.21 20:45, John Hubbard wrote:
> 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@...il.com>
>> Tested-by: Dmitry Osipenko <digetx@...il.com>
>> Suggested-by: Dmitry Osipenko <digetx@...il.com>
>> Suggested-by: John Hubbard <jhubbard@...dia.com>
>> Suggested-by: Matthew Wilcox <willy@...radead.org>
>> Signed-off-by: Minchan Kim <minchan@...nel.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.

Yes, that's what we should do in case it's not upstream yet. Clean 
resend + re-apply.


-- 
Thanks,

David / dhildenb