Re: [RFC 1/1] io_uring: preserve work->mm since actual work processing may need it

[Bijan Mottahedeh <bijan.mottahedeh@xxxxxxxxxx>]

> As I see, this down_read() from the trace is
> down_read(&current->mm->mmap_sem), where current->mm is set by use_mm()
> just several lines above your change. So, what do you mean by passing? I
> don't see do_madvise() __explicitly__ accepting mm as an argument.

I think the sequence is:

io_madvise()
-> do_madvise(NULL, req->work.mm, ma->addr, ma->len, ma->advice)
                    ^^^^^^^^^^^^
   -> down_read(&mm->mmap_sem)

I added an assert in do_madvise() for a NULL mm value and hit it running 
the test.

> What tree do you use? Extra patches on top?

I'm using next-20200409 with no patches.