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SubjectRe: lockdep warning: console vs. mem hotplug
On Sat, 25 Mar 2017 09:04:42 +0900
Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:

> On (03/21/17 13:44), Sergey Senozhatsky wrote:
> [..]
> > so we probably can
> >
> >
> > 1) move pr_info() out of zone->lock in __offline_isolated_pages().
> > meh...
> >
> >
> > 2) switch to printk_deferred() in __offline_isolated_pages().
> > meh.. there might a bunch of other printks done from under zone->lock.
> >
> >
> > 3) move add_timer() out of sclp_con_lock console in sclp_console_write().
> > well, there can be other consoles that do something similar.
> >
> >
> > 4) ... something smart.
>
>
> Sebastian, does this change make lockdep happy?
>
> it removes console drivers from the __offline_isolated_pages(). not the
> best solution I can think of, but the simplest one.
>
> ---
>
> mm/page_alloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f749b7ff7c50..eb61e6ab5f4f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7705,7 +7705,7 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
> BUG_ON(!PageBuddy(page));
> order = page_order(page);
> #ifdef CONFIG_DEBUG_VM
> - pr_info("remove from free list %lx %d %lx\n",
> + printk_deferred(KERN_INFO "remove from free list %lx %d %lx\n",
> pfn, 1 << order, end_pfn);
> #endif
> list_del(&page->lru);


My fear is that this will trigger for any printk in page_alloc.c under
the zone lock.

-- Steve

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