memcg && uaccess (Was: [PATCH 1/2] kernel/fork: handle put_user errors for CLONE_CHILD_SETTID/CLEARTID)

[Oleg Nesterov]

Add cc's.

On 02/06, Oleg Nesterov wrote:
>
> And in fact I think that this is not set_child_tid/etc-specific. Perhaps
> I am totally confused, but I think that put_user() simply should not fail
> this way. Say, why a syscall should return -EFAULT if memory allocation
> "silently" fails? Confused.

Seriously. I must have missed something, but I can't understand 519e52473eb
"mm: memcg: enable memcg OOM killer only for user faults".

The changelog says:

	System calls and kernel faults (uaccess, gup) can handle an out of
	memory situation gracefully and just return -ENOMEM.

How can a system call know it should return -ENOMEM if put_user() can only
return -EFAULT ?

Oleg.

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