linux-kernel - Re: [PATCH] Make radix_tree

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Date:	Fri, 28 Aug 2009 11:31:49 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	"Yan, Zheng " <yanzheng@...n.com>
Cc:	Zhu Yanhai <zhu.yanhai@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Huang Shijie <shijie8@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Zhu Yanhai <yanhai.zhu@...ux.intel.com>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH] Make radix_tree_preload alloc one more slot

On Fri, Aug 28, 2009 at 10:33:03AM +0800, Yan, Zheng  wrote:
> 2009/8/28 Wu Fengguang <fengguang.wu@...el.com>:
> > On Fri, Aug 28, 2009 at 12:46:46AM +0800, Yan, Zheng  wrote:
> >> 2009/8/27 Wu Fengguang <fengguang.wu@...el.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@...il.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

Ah yes!

> Oops, I suspect it's an radix_tree_preload bug. I told Zhu Yanhai
> my thought. Please forgive my rash act.

That's all right. So we can just do nothing? :)

Thanks,
Fengguang

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