linux-kernel - Re: unused swap offset / bad page map.

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Date:	Mon, 19 Aug 2013 19:18:36 -0400
From:	Dave Jones <davej@...hat.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	linux-mm@...ck.org, Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: unused swap offset / bad page map.

On Thu, Aug 08, 2013 at 11:20:28PM +0800, Hillf Danton wrote:
 > On Wed, Aug 7, 2013 at 11:30 PM, Dave Jones <davej@...hat.com> wrote:
 > > printk didn't trigger.
 > >
 > Is a corrupted page table entry encountered, according to the
 > comment of swap_duplicate()?
 > 
 > 
 > --- a/mm/swapfile.c	Wed Aug  7 17:27:22 2013
 > +++ b/mm/swapfile.c	Thu Aug  8 23:12:30 2013
 > @@ -770,6 +770,7 @@ int free_swap_and_cache(swp_entry_t entr
 >  		unlock_page(page);
 >  		page_cache_release(page);
 >  	}
 > +	return 1;
 >  	return p != NULL;
 >  }
 > 
 > --

[sorry for delay, been travelling]

With this applied, I no longer see the 'bad page' warning, but 
I do still get a bunch of messages like..

[  340.342436] swap_free: Unused swap offset entry 00003bb4
[  340.952980] swap_free: Unused swap offset entry 0000298d
[  340.953016] swap_free: Unused swap offset entry 00002996
[  340.953048] swap_free: Unused swap offset entry 0000299d


btw, anyone have thoughts on a patch something like below ?
It's really annoying to debug stuff like this and have to walk
over to the machine and reboot it by hand after it wedges during swapoff.

	Dave

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6cf2e60..bbb1192 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1587,6 +1587,10 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
+	/* If we have hit memory corruption, we could hang during swapoff, so don't even try. */
+	if (test_taint(TAINT_BAD_PAGE))
+		return -EINVAL;
+
 	BUG_ON(!current->mm);
 
 	pathname = getname(specialfile);
--
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