Re: [BUG] kmemleak on __radix_tree_preload

Catalin Marinas
2014-05-07T11:40:19Z

On Wed, May 07, 2014 at 03:58:08AM +0100, Jaegeuk Kim wrote:
> And then when I tested again with Catalin's patch, it still throws the
> following warning.
> Is it false alarm?

BTW, you can try this kmemleak branch:

git://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/linux-aarch64.git kmemleak

> 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?

Could you please send us your .config file?

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).

Thanks.

--
Catalin