On 4/10/2020 10:51 AM, Pavel Begunkov wrote:
On 10/04/2020 19:54, Bijan Mottahedeh wrote:
As I see, this down_read() from the trace is
down_read(¤t->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.
I see, it came from 676a179 ("mm: pass task and mm to do_madvise"), which isn't
in Jen's tree.
I don't think your patch will do, because it changes mm refcounting with extra
mmdrop() in io_req_work_drop_env(). That's assuming it worked well before.
Better fix then is to make it ```do_madvise(NULL, current->mm, ...)```
as it actually was at some point in the mentioned patch (v5).
Ok. Jens had suggested to use req->work.mm in the patch comments so
let's just get him to confirm:
"I think we want to use req->work.mm here - it'll be the same as
current->mm at this point, but it makes it clear that we're using a
grabbed mm."
