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

[David Hildenbrand]

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@xxxxxxxxx/
> > [2] https://lore.kernel.org/linux-mm/fead70a2-4330-79ff-e79a-d8511eab1256@xxxxxxxxx/
> > [3] https://lore.kernel.org/linux-mm/20210323195050.2577017-1-minchan@xxxxxxxxxx/
> > [4] https://lore.kernel.org/linux-mm/20210324010547.4134370-1-minchan@xxxxxxxxxx/
> >
> > Reported-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > Tested-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > Suggested-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > Suggested-by: John Hubbard <jhubbard@xxxxxxxxxx>
> > Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> > ---
> > 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