Re: [PATCH] Make radix_tree_preload alloc one more slot

Yan, Zheng
2009-08-28T02:33:05Z

2009/8/28 Wu Fengguang <fengguang.wu@intel.com>:
> On Fri, Aug 28, 2009 at 12:46:46AM +0800, Yan, Zheng  wrote:
>> 2009/8/27 Wu Fengguang <fengguang.wu@intel.com>:
>> >
>> > Hi Yanhai,
>> >
>> > [Nick CCed]
>> >
>> > On Thu, Aug 27, 2009 at 08:10:41PM +0800, Zhu Yanhai wrote:
>> >> The operations against radix tree always use paths with RADIX_TREE_MAX_PATH
>> >> + 1 slots, but radix_tree_preload only pre-allocs RADIX_TREE_MAX_PATH
>> >> slots at present, which causes radix_tree_node_alloc tries to do
>> >> kmem_cache_alloc at the last slot even if we don't have gfp_mask &
>> >> __GFP_WAIT in hand.
>> >
>> > Are you sure?  The comments read:
>> >
>> >        /*
>> >         * The radix tree path needs to be one longer than the maximum path
>> >         * since the "list" is null terminated.
>> >         */
>> >        struct radix_tree_path path[RADIX_TREE_MAX_PATH + 1], *pathp = path;
>> >
>> > Thanks,
>> > Fengguang
>> >
>> >
>> >> Signed-off-by: Zhu Yanhai <zhu.yanhai@gmail.com>
>> >>
>> >> ---
>> >>  lib/radix-tree.c |    2 +-
>> >>  1 files changed, 1 insertions(+), 1 deletions(-)
>> >>
>> >> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
>> >> index 23abbd9..72225a8 100644
>> >> --- a/lib/radix-tree.c
>> >> +++ b/lib/radix-tree.c
>> >> @@ -79,7 +79,7 @@ static struct kmem_cache *radix_tree_node_cachep;
>> >>   */
>> >>  struct radix_tree_preload {
>> >>       int nr;
>> >> -     struct radix_tree_node *nodes[RADIX_TREE_MAX_PATH];
>> >> +     struct radix_tree_node *nodes[RADIX_TREE_MAX_PATH + 1];
>> >>  };
>> >>  static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
>> >>
>> >> --
>> >> 1.6.2.2
>>
>> here is test case.
>> ---
>> #include <linux/module.h>
>> #include <linux/kernel.h>
>> #include <linux/radix-tree.h>
>>
>> static void __exit exit_test(void)
>> {
>> }
>>
>> static int __init init_test(void)
>> {
>>         struct radix_tree_root radix_tree;
>>         int foo;
>>
>>         INIT_RADIX_TREE(&radix_tree, GFP_KERNEL);
>>         radix_tree_preload(GFP_KERNEL);
>>         preempt_disable();
>>         radix_tree_insert(&radix_tree, (unsigned long)-2, &foo);
>>         preempt_enable();
>>         radix_tree_preload_end();
>>         radix_tree_delete(&radix_tree, (unsigned long)-2);
>>         return -1;
>> }
>>
>> module_init(init_test)
>> module_exit(exit_test)
>> MODULE_LICENSE("GPL");
>> -- end --
>>
>> I got following oops.
>> ---
>> BUG: sleeping function called from invalid context at
>> /home/zhyan/linux-2.6/mm/slub.c:1697
>> in_atomic(): 1, irqs_disabled(): 0, pid: 2791, name: insmod
>> Pid: 2791, comm: insmod Not tainted 2.6.31-rc7 #1
>> Call Trace:
>>  [<c042b26a>] __might_sleep+0x101/0x108
>>  [<c04b3976>] kmem_cache_alloc+0x39/0x141
>>  [<c05453c7>] ? radix_tree_node_alloc+0x4c/0x5d
>>  [<c05453c7>] radix_tree_node_alloc+0x4c/0x5d
>>  [<c054549a>] radix_tree_insert+0xc2/0x174
>>  [<f90cd03f>] init_test+0x3f/0x89 [test]
>>  [<c0401141>] do_one_initcall+0x4f/0x11f
>>  [<f90cd000>] ? init_test+0x0/0x89 [test]
>>  [<c044e504>] ? __blocking_notifier_call_chain+0x45/0x51
>>  [<c045d833>] sys_init_module+0xac/0x1bc
>>  [<c0403458>] sysenter_do_call+0x12/0x2d
>> -- end --
> This is weird, I cannot reproduce this message. Here is my .config.
> I use SLAB but it also has the might_sleep_if(__GFP_WAIT) debug call.
> Thanks,
> Fengguang

I realize it's my fault, I use GFP_KERNEL to initialize the radix tree.
radix_tree_node_alloc does not use pre-loaded memory when the
radix tree is initialized with GFP_KERNEL. Yesterday when I saw the
Oops, I suspect it's an radix_tree_preload bug. I told Zhu Yanhai
my thought. Please forgive my rash act.

Regards
Yan, Zheng