From: Jan Kara <jack@suse.cz>
To: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>,
"Huang, Ying" <ying.huang@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Hugh Dickins <hughd@google.com>,
"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Tim Chen <tim.c.chen@linux.intel.com>, Shaohua Li <shli@fb.com>,
Mel Gorman <mgorman@techsingularity.net>,
J???r???me Glisse <jglisse@redhat.com>,
Michal Hocko <mhocko@suse.com>,
Andrea Arcangeli <aarcange@redhat.com>,
David Rientjes <rientjes@google.com>,
Rik van Riel <riel@redhat.com>, Jan Kara <jack@suse.cz>,
Dave Jiang <dave.jiang@intel.com>, Aaron Lu <aaron.lu@intel.com>
Subject: Re: [PATCH -V4 -mm] mm, swap: Fix race between swapoff and some swap operations
Date: Tue, 2 Jan 2018 12:29:55 +0100 [thread overview]
Message-ID: <20180102112955.GA29170@quack2.suse.cz> (raw)
In-Reply-To: <20180102102103.mpah2ehglufwhzle@suse.de>
On Tue 02-01-18 10:21:03, Mel Gorman wrote:
> On Sat, Dec 23, 2017 at 10:36:53AM +0900, Minchan Kim wrote:
> > > code path. It appears that similar situation is possible for them too.
> > >
> > > The file cache pages will be delete from file cache address_space before
> > > address_space (embedded in inode) is freed. But they will be deleted
> > > from LRU list only when its refcount dropped to zero, please take a look
> > > at put_page() and release_pages(). While address_space will be freed
> > > after putting reference to all file cache pages. If someone holds a
> > > reference to a file cache page for quite long time, it is possible for a
> > > file cache page to be in LRU list after the inode/address_space is
> > > freed.
> > >
> > > And I found inode/address_space is freed witch call_rcu(). I don't know
> > > whether this is related to page_mapping().
> > >
> > > This is just my understanding.
> >
> > Hmm, it smells like a bug of __isolate_lru_page.
> >
> > Ccing Mel:
> >
> > What locks protects address_space destroying when race happens between
> > inode trauncation and __isolate_lru_page?
> >
>
> I'm just back online and have a lot of catching up to do so this is a rushed
> answer and I didn't read the background of this. However the question is
> somewhat ambiguous and the scope is broad as I'm not sure which race you
> refer to. For file cache pages, I wouldnt' expect the address_space to be
> destroyed specifically as long as the inode exists which is the structure
> containing the address_space in this case. A page on the LRU being isolated
> in __isolate_lru_page will have an elevated reference count which will
> pin the inode until remove_mapping is called which holds the page lock
> while inode truncation looking at a page for truncation also only checks
> page_mapping under the page lock. Very broadly speaking, pages avoid being
> added back to an inode being freed by checking the I_FREEING state.
So I'm wondering what prevents the following:
CPU1 CPU2
truncate(inode) __isolate_lru_page()
...
truncate_inode_page(mapping, page);
delete_from_page_cache(page)
spin_lock_irqsave(&mapping->tree_lock, flags);
__delete_from_page_cache(page, NULL)
page_cache_tree_delete(..)
... mapping = page_mapping(page);
page->mapping = NULL;
...
spin_unlock_irqrestore(&mapping->tree_lock, flags);
page_cache_free_page(mapping, page)
put_page(page)
if (put_page_testzero(page)) -> false
- inode now has no pages and can be freed including embedded address_space
if (mapping && !mapping->a_ops->migratepage)
- we've dereferenced mapping which is potentially already free.
This all seems very theoretical but in principle possible...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2018-01-02 11:30 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-20 1:26 [PATCH -V4 -mm] mm, swap: Fix race between swapoff and some swap operations Huang, Ying
2017-12-21 2:16 ` Minchan Kim
[not found] ` <871sjopllj.fsf@yhuang-dev.intel.com>
2017-12-21 23:58 ` Minchan Kim
2017-12-22 14:14 ` Huang, Ying
2017-12-22 16:14 ` Paul E. McKenney
2017-12-25 1:28 ` Huang, Ying
2017-12-23 1:36 ` Minchan Kim
2017-12-26 5:33 ` Huang, Ying
2018-01-02 10:21 ` Mel Gorman
2018-01-02 11:29 ` Jan Kara [this message]
2018-01-02 13:29 ` Mel Gorman
2018-01-03 0:42 ` Huang, Ying
2018-01-03 9:54 ` Mel Gorman
2018-01-04 1:17 ` Huang, Ying
2018-01-04 10:21 ` Mel Gorman
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