Message-ID: <20100609034452.GA28948@verge.net.au>
Date:	Wed, 9 Jun 2010 12:44:52 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Pavan Naregundi <pavan@...ux.vnet.ibm.com>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, vgoyal@...hat.com, hbabu@...ibm.com,
	kexec@...ts.infradead.org
Subject: Re: [PATCH] Fix Oops in crash_shrink_memory

On Tue, Jun 08, 2010 at 03:11:47PM +0530, Pavan Naregundi wrote:
> On Tue, 2010-06-08 at 16:54 +0800, Américo Wang wrote:
> > On Tue, Jun 08, 2010 at 02:10:05PM +0530, Pavan Naregundi wrote:
> > >On Tue, 2010-06-08 at 15:59 +0800, Américo Wang wrote:
> > >> On Tue, Jun 08, 2010 at 12:37:37PM +0530, Pavan Naregundi wrote:
> > >> >Adding CC's..
> > >> >
> > >> >
> > >> >On Mon, 2010-06-07 at 12:58 +0530, Pavan Naregundi wrote:
> > >> >> Hi Everyone,
> > >> >> 
> > >> >> Please add me to CC in your reply..
> > >> >> 
> > >> >> When crashkernel is not enabled, "echo 0 > /sys/kernel/kexec_crash_size"
> > >> >> will generate OOPS message in the kernel. Below is the OOPS message and
> > >> >> other details,
> > >> >> 
> > >> >> # cat /proc/cmdline 
> > >> >> ro  LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYTABLE=us console=hvc0
> > >> >> rhgb root=UUID=eafd9874-010c-46f9-a0c6-ea8db7c61ac3
> > >> >> # uname -a
> > >> >> Linux XXXXXXXX 2.6.35-rc1 #1 SMP Mon Jun 7 18:04:53 IST 2010 ppc64 ppc64
> > >> >> ppc64 GNU/Linux
> > >> >> # cd /sys/kernel/
> > >> >> # ls
> > >> >> debug               kexec_loaded  profiling      uevent_seqnum
> > >> >> kexec_crash_loaded  mm            security       vmcoreinfo
> > >> >> kexec_crash_size    notes         uevent_helper
> > >> >> # cat kexec_crash_loaded
> > >> >> 0
> > >> >> # cat kexec_loaded
> > >> >> 0
> > >> >> # cat kexec_crash_size
> > >> >> 1
> > >> >> # echo 0 > kexec_crash_size
> > >> >> Unable to handle kernel paging request for data at address 0x00000030
> > >> >> Faulting instruction address: 0xc0000000000930b4
> > >> >> Oops: Kernel access of bad area, sig: 11 [#1]
> > >> >> SMP NR_CPUS=1024 NUMA pSeries
> > >> >> last sysfs file: /sys/kernel/kexec_crash_size
> > >> >> Modules linked in: sunrpc ipv6 ext3 jbd dm_mirror dm_region_hash dm_log
> > >> >> dm_multipath dm_mod uinput sg ehea sr_mod ibmveth cdrom ext4 jbd2
> > >> >> mbcache sd_mod crc_t10dif ibmvscsic scsi_transport_srp scsi_tgt [last
> > >> >> unloaded: scsi_wait_scan]
> > >> >> NIP: c0000000000930b4 LR: c0000000000930ac CTR: c0000000000b7ce0
> > >> >> REGS: c0000000b7803750 TRAP: 0300   Not tainted  (2.6.35-rc1)
> > >> >> MSR: 8000000000009032 <EE,ME,IR,DR>  CR: 28242482  XER: 20000000
> > >> >> DAR: 0000000000000030, DSISR: 0000000040000000
> > >> >> TASK = c0000000b9cc3dc0[1381] 'bash' THREAD: c0000000b7800000 CPU: 12
> > >> >> GPR00: c0000000000930ac c0000000b78039d0 c000000000e885a8
> > >> >> c000000000f42950 
> > >> >> GPR04: c0000000b7803af0 0000000000000008 0000000000000002
> > >> >> c0000000005c6438 
> > >> >> GPR08: 0000000000000000 000000008000000c 0000000000000000
> > >> >> 0000000000000000 
> > >> >> GPR12: 0000000040242448 c000000007441e00 00000000100f6210
> > >> >> 0000000000000000 
> > >> >> GPR16: 00000000100f4a38 00000000100cfb98 00000000100f4bdc
> > >> >> 00000000100f4b4c 
> > >> >> GPR20: 00000000103f4de8 0000000000000000 0000000000000000
> > >> >> 00000000100f0000 
> > >> >> GPR24: c0000000005c65c0 0000000000000000 c000000000da83e0
> > >> >> c0000000bc67f780 
> > >> >> GPR28: c0000000bc684ae0 c000000000f42950 c000000000e1e3f8
> > >> >> c000000000da8408 
> > >> >> NIP [c0000000000930b4] .release_resource+0x34/0xe0
> > >> >> LR [c0000000000930ac] .release_resource+0x2c/0xe0
> > >> >> Call Trace:
> > >> >> [c0000000b78039d0] [c0000000000930ac] .release_resource+0x2c/0xe0
> > >> >> (unreliable)
> > >> >> [c0000000b7803a60] [c0000000000d4fc8] .crash_shrink_memory+0x1c8/0x1f0
> > >> >> [c0000000b7803b30] [c0000000000b7d38] .kexec_crash_size_store+0x58/0x90
> > >> >> [c0000000b7803bc0] [c0000000002b0bb4] .kobj_attr_store+0x34/0x50
> > >> >> [c0000000b7803c30] [c000000000226d5c] .sysfs_write_file+0xec/0x1f0
> > >> >> [c0000000b7803ce0] [c00000000019e0bc] .vfs_write+0xec/0x1f0
> > >> >> [c0000000b7803d80] [c00000000019e2e8] .SyS_write+0x58/0xb0
> > >> >> [c0000000b7803e30] [c00000000000852c] syscall_exit+0x0/0x40
> > >> >> Instruction dump:
> > >> >> fba1ffe8 fbc1fff0 fbe1fff8 ebc2b228 7c7f1b78 f8010010 f821ff71 ebbe8000 
> > >> >> 7fa3eb78 484e35d9 60000000 e97f0020 <e92b0030> 2fa90000 419e002c
> > >> >> 7fbf4800 
> > >> >> ---[ end trace afbc780462c9bf4e ]---
> > >> >> 
> > >> >> When crashkernel is not enabled, crashk_res resource have not been
> > >> >> reserved. Hence crashk_res.parent will be NULL.
> > >> >> 
> > >> >> Attaching a simple patch to this problem. Patch is tested and resolves this bug.
> > >> 
> > >> 
> > >> Ouch...
> > >> 
> > >> The patch indeed addresses the problem, looks good to me.
> > >> Please add your Signed-off-by and my:
> > >> 
> > >> Reviewed-by: WANG Cong <xiyou.wangcong@...il.com>
> > >> 
> > >> Another problem is that you should get 0 instead of 1 when you don't
> > >> reserve any memory.
> > >
> > >We get 1 here because, crash_get_memory_size() adds 1 as below, 
> > >
> > >size = crashk_res.end - crashk_res.start + 1;
> > >
> > >We cant remove this addition, as it is required to display correct size
> > >in case if we reserve the crash memory.
> > 
> > Yeah, but 0 is a special case, isn't it?
> 
> Yes, it is a special case.
> 
> Prepared a new patch which solves both of this issues.
> 
> 1. OOPs in crash_shrink_memory
> 2. make crash_get_memory_size to return correct size, in case of crash
> memory not reserved.
> 
> Patch is tested.
> 
> Thank You.
> 
> Signed-off-by: Pavan Naregundi <pavan@...ux.vnet.ibm.com>
> Reviewed-by: WANG Cong <xiyou.wangcong@...il.com>
> ---
> 
> 
> 

> diff -Naur a/kernel/kexec.c b/kernel/kexec.c
> --- a/kernel/kexec.c	2010-06-08 21:17:21.850000033 +0530
> +++ b/kernel/kexec.c	2010-06-08 21:19:26.190000043 +0530
> @@ -1089,9 +1089,10 @@
>  
>  size_t crash_get_memory_size(void)
>  {
> -	size_t size;
> +	size_t size = 0;
>  	mutex_lock(&kexec_mutex);
> -	size = crashk_res.end - crashk_res.start + 1;
> +	if(crashk_res.end != crashk_res.start)
> +		size = crashk_res.end - crashk_res.start + 1;

Minor style-issue: there should be a space between if and (.

>  	mutex_unlock(&kexec_mutex);
>  	return size;
>  }
> @@ -1134,7 +1135,7 @@
>  
>  	free_reserved_phys_range(end, crashk_res.end);
>  
> -	if (start == end)
> +	if ((start == end) && (crashk_res.parent != NULL))
>  		release_resource(&crashk_res);
>  	crashk_res.end = end - 1;
>  

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