netdev - Re: recent -git: BUG in free_thread

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Date:	Thu, 24 Jul 2008 00:50:49 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>,
	"Jeff Garzik" <jgarzik@...ox.com>
Cc:	"Suresh Siddha" <suresh.b.siddha@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>, netdev@...r.kernel.org
Subject: Re: recent -git: BUG in free_thread_xstate

On Thu, Jul 24, 2008 at 12:45 AM, Vegard Nossum <vegard.nossum@...il.com> wrote:
> Hey, with this patch applied:
>
> diff --git a/include/asm-x86/string_32.h b/include/asm-x86/string_32.h
> index b49369a..7bef7ea 100644
> --- a/include/asm-x86/string_32.h
> +++ b/include/asm-x86/string_32.h
> @@ -29,9 +29,14 @@ extern char *strchr(const char *s, int c);
>  #define __HAVE_ARCH_STRLEN
>  extern size_t strlen(const char *s);
>
> +extern void warn_on_slowpath(const char *file, int line);
> +
>  static __always_inline void * __memcpy(void * to, const void * from, size_t n)
>  {
>  int d0, d1, d2;
> +       if (n == 0x6b)
> +               warn_on_slowpath(__FILE__, __LINE__);
> +
>  __asm__ __volatile__(
>        "rep ; movsl\n\t"
>        "movl %4,%%ecx\n\t"
>
> I have found an important clue; it seems to be my network driver's fault:
>
> ------------[ cut here ]------------
> WARNING: at include2/asm/string_32.h:38 skb_copy_and_csum_dev+0xee/0x100()
> Pid: 3989, comm: bash Tainted: G        W 2.6.26-dirty #3
>  [<c013496f>] warn_on_slowpath+0x4f/0x70
>  [<c0198041>] ? check_bytes_and_report+0x21/0xc0
>  [<c04a8544>] ? __kfree_skb+0x34/0x80
>  [<c0198041>] ? check_bytes_and_report+0x21/0xc0
>  [<c01983ef>] ? check_object+0xdf/0x1f0
>  [<c0198041>] ? check_bytes_and_report+0x21/0xc0
>  [<c04a8544>] ? __kfree_skb+0x34/0x80
>  [<c01983ef>] ? check_object+0xdf/0x1f0
>  [<c04bbafc>] ? find_skb+0x3c/0x80
>  [<c04a9f7e>] skb_copy_and_csum_dev+0xee/0x100
>  [<c03539d7>] rtl8139_start_xmit+0x57/0x130
>  [<c019a84b>] ? __kmalloc_track_caller+0x8b/0x120
>  [<c04bba6e>] netpoll_send_skb+0x14e/0x1a0
>  [<c04bbf54>] netpoll_send_udp+0x1e4/0x210
>  [<c0374b0c>] write_msg+0x8c/0xc0
>  [<c0135053>] __call_console_drivers+0x53/0x60
>  [<c01350ab>] _call_console_drivers+0x4b/0x90
>  [<c01351f5>] release_console_sem+0xc5/0x1f0
>  [<c01357fe>] vprintk+0x2ce/0x420
>  [<c0107e7d>] ? do_IRQ+0x4d/0xa0
>  [<c0104de5>] ? restore_nocheck+0x12/0x15
>  [<c0286ae1>] ? delay_tsc+0x61/0xb8
>  [<c0286b06>] ? delay_tsc+0x86/0xb8
>  [<c013596b>] printk+0x1b/0x20
>  [<c0580d5d>] native_cpu_up+0x7cd/0x880
>  [<c01df741>] ? internal_create_group+0xd1/0x180
>  [<c0580470>] ? do_fork_idle+0x0/0x20
>  [<c014d7c9>] ? __raw_notifier_call_chain+0x19/0x20
>  [<c05826f3>] _cpu_up+0x83/0x100
>  [<c05827b9>] cpu_up+0x49/0x70
>  [<c05635d8>] store_online+0x58/0x80
>  [<c0563580>] ? store_online+0x0/0x80
>  [<c02fda2b>] sysdev_store+0x2b/0x40
>  [<c01dd7b2>] sysfs_write_file+0xa2/0x100
>  [<c019f156>] vfs_write+0x96/0x130
>  [<c01dd710>] ? sysfs_write_file+0x0/0x100
>  [<c019f81d>] sys_write+0x3d/0x70
>  [<c0104cdb>] sysenter_past_esp+0x78/0xd1
>  =======================
> ---[ end trace a7919e7f17c0a725 ]---
>
> In particular, these are interesting:
>
>  [<c04a9f7e>] skb_copy_and_csum_dev+0xee/0x100
>
> This is net/core/skbuff.c:1731:
>        skb_copy_from_linear_data(skb, to, csstart);
>
>  [<c03539d7>] rtl8139_start_xmit+0x57/0x130
>
> This is drivers/net/8139too.c:1711:
>                dev_kfree_skb(skb);
>

Oops, this should of course be the line just above (because the
address on the stack is the return address...), which is:

                skb_copy_and_csum_dev(skb, tp->tx_buf[entry]);

(Big surprise there ;-))

> (The line numbers are still from v2.6.26, but this reproduces on
> current -git as well.)
>
> Is this enough information to fix it? :-)

I've also added Jeff Garzik to Cc since he seems to be the maintainer
of this driver.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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