Re: mm: hangs in free_pages_prepare

[Michal Hocko <mhocko@suse.cz>]

On Sat 07-03-15 13:38:08, Sasha Levin wrote:
[...]
> [ 1573.730097] ? kasan_free_pages (mm/kasan/kasan.c:301)
> [ 1573.788680] free_pages_prepare (mm/page_alloc.c:791)
> [ 1573.788680] ? free_hot_cold_page (./arch/x86/include/asm/paravirt.h:809 (discriminator 2) mm/page_alloc.c:1579 (discriminator 2))
> [ 1573.788680] free_hot_cold_page (mm/page_alloc.c:1543)
> [ 1573.788680] __free_pages (mm/page_alloc.c:2957)
> [ 1573.788680] ? __vunmap (mm/vmalloc.c:1460 (discriminator 2))
> [ 1573.788680] __vunmap (mm/vmalloc.c:1460 (discriminator 2))

__vunmap is doing:
                for (i = 0; i < area->nr_pages; i++) {
                        struct page *page = area->pages[i];

                        BUG_ON(!page);
                        __free_page(page);
                }

is it possible that nr_pages is a huge number (a large vmalloc area)? I
do not see any cond_resched down __free_page path at least. vfree
delayes the call to workqueue when called from irq context and vunmap is
marked as might_sleep). So to me it looks like it would be safe. Something
for vmalloc familiar people, though.

Anyway, the loop seems to be there since ages so I guess somebody just
started calling vmalloc for huge areas recently so it shown up.
-- 
Michal Hocko
SUSE Labs

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