Re: [PATCH] mm: cma: fix corruption cma_sysfs_alloc_pages_count

[John Hubbard <jhubbard@nvidia.com>]

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