Just test sent by misstake, please ignore it (sorry for the disturb) //答复: [PATCH] afs: fix tracepoint string placement with built-in AFS

Just test sent by misstake, please ignore it (sorry for the disturb) //答复: [PATCH] afs: fix tracepoint string placement with built-in AFS

[Zengtao (B)]

Hi guys: 

Very for the sorry for disturbs, this is a test for local git send email setup and sent by mistake. 
Please ignore this. 

Regards
Zengtao 

> -----邮件原件-----
> 发件人: Zengtao (B)
> 发送时间: 2021年6月22日 14:52
> 收件人: Zengtao (B) <prime.zeng@hisilicon.com>
> 抄送: Alexey Dobriyan <adobriyan@gmail.com>; Andi Kleen <andi@firstfloor.org>;
> David Howells <dhowells@redhat.com>; stable@vger.kernel.org; Andrew Morton
> <akpm@linux-foundation.org>; Stephen Rothwell <sfr@canb.auug.org.au>
> 主题: [PATCH] afs: fix tracepoint string placement with built-in AFS
> 
> From: Alexey Dobriyan <adobriyan@gmail.com>
> 
> I was adding custom tracepoint to the kernel, grabbed full F34 kernel
> .config, disabled modules and booted whole shebang as VM kernel.
> 
> Then did
> 
> 	perf record -a -e ...
> 
> It crashed:
> 
> 	general protection fault, probably for non-canonical address
> 0x435f5346592e4243: 0000 [#1] SMP PTI
> 	CPU: 1 PID: 842 Comm: cat Not tainted 5.12.6+ #26
> 	Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33
> 04/01/2014
> 	RIP: 0010:t_show+0x22/0xd0
> 
> Then reproducer was narrowed to
> 
> 	# cat /sys/kernel/tracing/printk_formats
> 
> Original F34 kernel with modules didn't crash.
> 
> So I started to disable options and after disabling AFS everything started
> working again.
> 
> The root cause is that AFS was placing char arrays content into a section
> full of _pointers_ to strings with predictable consequences.
> 
> Non canonical address 435f5346592e4243 is "CB.YFS_" which came from
> CM_NAME macro.
> 
> The fix is to create char array and pointer to it separatedly.
> 
> Steps to reproduce:
> 
> 	CONFIG_AFS=y
> 	CONFIG_TRACING=y
> 
> 	# cat /sys/kernel/tracing/printk_formats
> 
> Link: https://lkml.kernel.org/r/YLAXfvZ+rObEOdc/@localhost.localdomain
> Fixes: 8e8d7f13b6d5a9 ("afs: Add some tracepoints")
> Signed-off-by: Alexey Dobriyan (SK hynix) <adobriyan@gmail.com>
> Cc: Andi Kleen <andi@firstfloor.org>
> Cc: David Howells <dhowells@redhat.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
> ---
>  fs/afs/cmservice.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/afs/cmservice.c b/fs/afs/cmservice.c
> index d3c6bb22c5f4..d39c63b13d9f 100644
> --- a/fs/afs/cmservice.c
> +++ b/fs/afs/cmservice.c
> @@ -30,8 +30,9 @@ static void SRXAFSCB_TellMeAboutYourself(struct
> work_struct *);
>  static int afs_deliver_yfs_cb_callback(struct afs_call *);
> 
>  #define CM_NAME(name) \
> -	char afs_SRXCB##name##_name[] __tracepoint_string =	\
> -		"CB." #name
> +	const char afs_SRXCB##name##_name[] = "CB." #name;		\
> +	static const char *_afs_SRXCB##name##_name __tracepoint_string =\
> +		afs_SRXCB##name##_name
> 
>  /*
>   * CB.CallBack operation type
> --
> 2.30.0