From: Catalin Marinas <catalin.marinas@arm.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jaegeuk Kim <jaegeuk.kim@samsung.com>,
Johannes Weiner <hannes@cmpxchg.org>,
"Linux Kernel, Mailing List" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [BUG] kmemleak on __radix_tree_preload
Date: Thu, 8 May 2014 17:52:17 +0100 [thread overview]
Message-ID: <20140508165217.GI17344@arm.com> (raw)
In-Reply-To: <20140508155330.GE8754@linux.vnet.ibm.com>
On Thu, May 08, 2014 at 04:53:30PM +0100, Paul E. McKenney wrote:
> On Thu, May 08, 2014 at 04:29:48PM +0100, Catalin Marinas wrote:
> > BTW, is it safe to have a union overlapping node->parent and
> > node->rcu_head.next? I'm still staring at the radix-tree code but a
> > scenario I have in mind is that call_rcu() has been raised for a few
> > nodes, other CPU may have some reference to one of them and set
> > node->parent to NULL (e.g. concurrent calls to radix_tree_shrink()),
> > breaking the RCU linking. I can't confirm this theory yet ;)
>
> If this were reproducible, I would suggest retrying with non-overlapping
> node->parent and node->rcu_head.next, but you knew that already. ;-)
Reading the code, I'm less convinced about this scenario (though it's
worth checking without the union).
> But the usual practice would be to make node removal exclude shrinking.
> And the radix-tree code seems to delegate locking to the caller.
>
> So, is the correct locking present in the page cache? The radix-tree
> code seems to assume that all update operations for a given tree are
> protected by a lock global to that tree.
The calling code in mm/filemap.c holds mapping->tree_lock when deleting
radix-tree nodes, so no concurrent calls.
> Another diagnosis approach would be to build with
> CONFIG_DEBUG_OBJECTS_RCU_HEAD=y, which would complain about double
> call_rcu() invocations. Rumor has it that is is necessary to turn off
> other kmem debugging for this to tell you anything -- I have seen cases
> where the kmem debugging obscures the debug-objects diagnostics.
Another test Jaegeuk could run (hopefully he has some time to look into
this).
Thanks for suggestions.
--
Catalin
next prev parent reply other threads:[~2014-05-08 16:53 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-25 1:45 [BUG] kmemleak on __radix_tree_preload Jaegeuk Kim
2014-05-01 17:06 ` Catalin Marinas
2014-05-01 18:41 ` Johannes Weiner
2014-05-07 2:58 ` Jaegeuk Kim
2014-05-07 11:39 ` Catalin Marinas
2014-05-08 9:16 ` Jaegeuk Kim
2014-05-08 9:26 ` Catalin Marinas
2014-05-08 9:37 ` Jaegeuk Kim
2014-05-08 10:24 ` Catalin Marinas
2014-05-08 15:00 ` Paul E. McKenney
2014-05-08 15:29 ` Catalin Marinas
2014-05-08 15:53 ` Paul E. McKenney
2014-05-08 16:52 ` Catalin Marinas [this message]
2014-05-09 0:06 ` Jaegeuk Kim
2014-05-08 17:52 ` Johannes Weiner
2014-05-08 21:40 ` Catalin Marinas
2014-05-09 0:01 ` Jaegeuk Kim
2014-05-09 9:45 ` Catalin Marinas
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