linux-kernel - Re: lockdep warning: console vs. mem hotplug

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Message-ID: <20170325000442.GD6356@tigerII.localdomain>
Date:   Sat, 25 Mar 2017 09:04:42 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Sebastian Ott <sebott@...ux.vnet.ibm.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: lockdep warning: console vs. mem hotplug

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);