linux-kernel - Re: [BUG] kmemleak on __radix_tree

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Date:	Thu, 08 May 2014 18:37:40 +0900
From:	Jaegeuk Kim <jaegeuk.kim@...sung.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	"Linux Kernel, Mailing List" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [BUG] kmemleak on __radix_tree_preload

2014-05-08 (목), 10:26 +0100, Catalin Marinas:
> On Thu, May 08, 2014 at 06:16:51PM +0900, Jaegeuk Kim wrote:
> > 2014-05-07 (수), 12:39 +0100, Catalin Marinas:
> > > On Wed, May 07, 2014 at 03:58:08AM +0100, Jaegeuk Kim wrote:
> > > > unreferenced object 0xffff880004226da0 (size 576):
> > > >   comm "fsstress", pid 14590, jiffies 4295191259 (age 706.308s)
> > > >   hex dump (first 32 bytes):
> > > >     01 00 00 00 81 ff ff ff 00 00 00 00 00 00 00 00  ................
> > > >     50 89 34 81 ff ff ff ff b8 6d 22 04 00 88 ff ff  P.4......m".....
> > > >   backtrace:
> > > >     [<ffffffff816c02e8>] kmemleak_update_trace+0x58/0x80
> > > >     [<ffffffff81349517>] radix_tree_node_alloc+0x77/0xa0
> > > >     [<ffffffff81349718>] __radix_tree_create+0x1d8/0x230
> > > >     [<ffffffff8113286c>] __add_to_page_cache_locked+0x9c/0x1b0
> > > >     [<ffffffff811329a8>] add_to_page_cache_lru+0x28/0x80
> > > >     [<ffffffff81132f58>] grab_cache_page_write_begin+0x98/0xf0
> > > >     [<ffffffffa02e4bf4>] f2fs_write_begin+0xb4/0x3c0 [f2fs]
> > > >     [<ffffffff81131b77>] generic_perform_write+0xc7/0x1c0
> > > >     [<ffffffff81133b7d>] __generic_file_aio_write+0x1cd/0x3f0
> > > >     [<ffffffff81133dfe>] generic_file_aio_write+0x5e/0xe0
> > > >     [<ffffffff81195c5a>] do_sync_write+0x5a/0x90
> > > >     [<ffffffff811968d2>] vfs_write+0xc2/0x1d0
> > > >     [<ffffffff81196daf>] SyS_write+0x4f/0xb0
> > > >     [<ffffffff816dead2>] system_call_fastpath+0x16/0x1b
> > > >     [<ffffffffffffffff>] 0xffffffffffffffff
> > > 
> > > OK, it shows that the allocation happens via add_to_page_cache_locked()
> > > and I guess it's page_cache_tree_insert() which calls
> > > __radix_tree_create() (the latter reusing the preloaded node). I'm not
> > > familiar enough to this code (radix-tree.c and filemap.c) to tell where
> > > the node should have been freed, who keeps track of it.
> > > 
> > > At a quick look at the hex dump (assuming that the above leak is struct
> > > radix_tree_node):
> > > 
> > > 	.path = 1
> > > 	.count = -0x7f (or 0xffffff81 as unsigned int)
> > > 	union {
> > > 		{
> > > 			.parent = NULL
> > > 			.private_data = 0xffffffff81348950
> > > 		}
> > > 		{
> > > 			.rcu_head.next = NULL
> > > 			.rcu_head.func = 0xffffffff81348950
> > > 		}
> > > 	}
> > > 
> > > The count is a bit suspicious.
> > > 
> > > From the union, it looks most likely like rcu_head information. Is
> > > radix_tree_node_rcu_free() function at the above rcu_head.func?
> 
> Thanks for the config. Could you please confirm that 0xffffffff81348950
> address corresponds to the radix_tree_node_rcu_free() function in your
> System.map (or something else)?

Yap, the address is matched to radix_tree_node_rcu_free().
Thanks,

> 
> > > Also, if you run echo scan > /sys/kernel/debug/kmemleak a few times, do
> > > any of the above leaks disappear (in case the above are some transient
> > > rcu freeing reports; normally this shouldn't happen as the objects are
> > > still referred but I'll look at the relevant code once I have your
> > > .config).
> > 
> > Once I run the echo, the leaks are still remained.
> 
> OK, so they aren't just transient.
> 
> Thanks.
> 

-- 
Jaegeuk Kim
Samsung

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