Re: [mm/vmalloc] 5c1f4e690e: BUG:sleeping_function_called_from_invalid_context_at_mm/page_alloc.c

[Mel Gorman]

On Tue, Jul 13, 2021 at 11:19:29AM -0700, Linus Torvalds wrote:
> On Tue, Jul 13, 2021 at 7:06 AM kernel test robot <oliver.sang@xxxxxxxxx> wrote:
> >
> > [  131.014885] BUG: sleeping function called from invalid context at mm/page_alloc.c:4992
> 
> Strange. The call chain doesn't actually seem to be anything off: it's
> writev -> sock_write_iter -> sock_sendmsg -> netlink_sendmsg ->
> vmalloc.
> 
> All good to sleep as far as I can tell. The warning itself seems to be just
> 
>         might_sleep_if(gfp_mask & __GFP_DIRECT_RECLAIM);
> 
> in prepare_alloc_pages().
> 
> I don't see what's wrong with that commit, but it does seem to be very
> consistent, in that the parent doesn't have it:
> 

It's almost certainly going to be fixed by
https://lore.kernel.org/r/20210713152100.10381-2-mgorman@xxxxxxxxxxxxxxxxxxx
whenever it hits your tree as part of this series
https://lore.kernel.org/lkml/20210713152100.10381-1-mgorman@xxxxxxxxxxxxxxxxxxx/.
It should make its way through Andrew's tree before RC2 but if he is busy
I'll create a git pull request.

> which means that the might_sleep_if() happens _after_
> __alloc_pages_bulk() has disabled interrupts. That would explain it,
> but the stack_depot_save() thing actually makes that call chain really
> hard to read because it duplicates the addresses on the stack.
> 
> I don't see the nesting there, but that's what it kind of smells like to me.
> 
> Anybody?
> 

The problem is that PAGE_OWNER can recurse allocate from bulk allocation
context to store the caller stack. When I wrote the patch, I missed that
prep_new_page can allocate if PAGE_OWNER is active. The most relevant
part of the trace is

[  131.092667]  stack_depot_save+0x390/0x4c0

-- 
Mel Gorman
SUSE Labs