Re: [BUG] kmemleak on __radix_tree_preload

Catalin Marinas
2014-05-08T09:27:35Z

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)?

> > 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.

--
Catalin