Re: [PATCH v03] powerpc/mobility: Fix node detach/rename problem

[Michael Bringmann]

On 12/11/2018 07:29 AM, Michael Ellerman wrote:
> Hi Michael,
> 
> Please Cc the device tree folks on device tree patches, and also the
> original author of the patch that added the code you're modifying.
> 
> So I've added:
>   robh+dt@xxxxxxxxxx
>   frowand.list@xxxxxxxxx
>   devicetree@xxxxxxxxxxxxxxx
>   linux-kernel@xxxxxxxxxxxxxxx

Thanks.

> 
> Michael Bringmann <mwb@xxxxxxxxxxxxxxxxxx> writes:
>> The PPC mobility code receives RTAS requests to delete nodes with
>> platform-/hardware-specific attributes when restarting the kernel
>> after a migration.  My example is for migration between a P8 Alpine
>> and a P8 Brazos.   Nodes to be deleted include 'ibm,random-v1',
>> 'ibm,platform-facilities', 'ibm,sym-encryption-v1', and,
>> 'ibm,compression-v1'.
>>
>> The mobility.c code calls 'of_detach_node' for the nodes and their
>> children.  This makes calls to detach the properties and to remove
>> the associated sysfs/kernfs files.
>>
>> Then new copies of the same nodes are next provided by the PHYP,
>> local copies are built, and a pointer to the 'struct device_node'
>> is passed to of_attach_node.  Before the call to of_attach_node,
>> the phandle is initialized to 0 when the data structure is alloced.
>> During the call to of_attach_node, it calls __of_attach_node which
>> pulls the actual name and phandle from just created sub-properties
>> named something like 'name' and 'ibm,phandle'.
>>
>> This is all fine for the first migration.  The problem occurs with
>> the second and subsequent migrations when the PHYP on the new system
>> wants to replace the same set of nodes again, referenced with the
>> same names and phandle values.
>>
>> On the second and subsequent migrations, the PHYP tells the system
>> to again delete the nodes 'ibm,platform-facilities', 'ibm,random-v1',
>> 'ibm,compression-v1', 'ibm,sym-encryption-v1'.  It specifies these
>> nodes by its known set of phandle values -- the same handles used
>> by the PHYP on the source system are known on the target system.
>> The mobility.c code calls of_find_node_by_phandle() with these values
>> and ends up locating the first instance of each node that was added
>> during the original boot, instead of the second instance of each node
>> created after the first migration.  The detach during the second
>> migration fails with errors like,
>>
>> [ 4565.030704] WARNING: CPU: 3 PID: 4787 at drivers/of/dynamic.c:252 __of_detach_node+0x8/0xa0
>> [ 4565.030708] Modules linked in: nfsv3 nfs_acl nfs tcp_diag udp_diag inet_diag unix_diag af_packet_diag netlink_diag lockd grace fscache sunrpc xts vmx_crypto sg pseries_rng binfmt_misc ip_tables xfs libcrc32c sd_mod ibmveth ibmvscsi scsi_transport_srp dm_mirror dm_region_hash dm_log dm_mod
>> [ 4565.030733] CPU: 3 PID: 4787 Comm: drmgr Tainted: G        W         4.18.0-rc1-wi107836-v05-120+ #201
>> [ 4565.030737] NIP:  c0000000007c1ea8 LR: c0000000007c1fb4 CTR: 0000000000655170
>> [ 4565.030741] REGS: c0000003f302b690 TRAP: 0700   Tainted: G        W          (4.18.0-rc1-wi107836-v05-120+)
>> [ 4565.030745] MSR:  800000010282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]>  CR: 22288822  XER: 0000000a
>> [ 4565.030757] CFAR: c0000000007c1fb0 IRQMASK: 1
>> [ 4565.030757] GPR00: c0000000007c1fa4 c0000003f302b910 c00000000114bf00 c0000003ffff8e68
>> [ 4565.030757] GPR04: 0000000000000001 ffffffffffffffff 800000c008e0b4b8 ffffffffffffffff
>> [ 4565.030757] GPR08: 0000000000000000 0000000000000001 0000000080000003 0000000000002843
>> [ 4565.030757] GPR12: 0000000000008800 c00000001ec9ae00 0000000040000000 0000000000000000
>> [ 4565.030757] GPR16: 0000000000000000 0000000000000008 0000000000000000 00000000f6ffffff
>> [ 4565.030757] GPR20: 0000000000000007 0000000000000000 c0000003e9f1f034 0000000000000001
>> [ 4565.030757] GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>> [ 4565.030757] GPR28: c000000001549d28 c000000001134828 c0000003ffff8e68 c0000003f302b930
>> [ 4565.030804] NIP [c0000000007c1ea8] __of_detach_node+0x8/0xa0
>> [ 4565.030808] LR [c0000000007c1fb4] of_detach_node+0x74/0xd0
>> [ 4565.030811] Call Trace:
>> [ 4565.030815] [c0000003f302b910] [c0000000007c1fa4] of_detach_node+0x64/0xd0 (unreliable)
>> [ 4565.030821] [c0000003f302b980] [c0000000000c33c4] dlpar_detach_node+0xb4/0x150
>> [ 4565.030826] [c0000003f302ba10] [c0000000000c3ffc] delete_dt_node+0x3c/0x80
>> [ 4565.030831] [c0000003f302ba40] [c0000000000c4380] pseries_devicetree_update+0x150/0x4f0
>> [ 4565.030836] [c0000003f302bb70] [c0000000000c479c] post_mobility_fixup+0x7c/0xf0
>> [ 4565.030841] [c0000003f302bbe0] [c0000000000c4908] migration_store+0xf8/0x130
>> [ 4565.030847] [c0000003f302bc70] [c000000000998160] kobj_attr_store+0x30/0x60
>> [ 4565.030852] [c0000003f302bc90] [c000000000412f14] sysfs_kf_write+0x64/0xa0
>> [ 4565.030857] [c0000003f302bcb0] [c000000000411cac] kernfs_fop_write+0x16c/0x240
>> [ 4565.030862] [c0000003f302bd00] [c000000000355f20] __vfs_write+0x40/0x220
>> [ 4565.030867] [c0000003f302bd90] [c000000000356358] vfs_write+0xc8/0x240
>> [ 4565.030872] [c0000003f302bde0] [c0000000003566cc] ksys_write+0x5c/0x100
>> [ 4565.030880] [c0000003f302be30] [c00000000000b288] system_call+0x5c/0x70
>> [ 4565.030884] Instruction dump:
>> [ 4565.030887] 38210070 38600000 e8010010 eb61ffd8 eb81ffe0 eba1ffe8 ebc1fff0 ebe1fff8
>> [ 4565.030895] 7c0803a6 4e800020 e9230098 7929f7e2 <0b090000> 2f890000 4cde0020 e9030040
>> [ 4565.030903] ---[ end trace 5bd54cb1df9d2976 ]---
>>
>> The mobility.c code continues on during the second migration, accepts
>> the definitions of the new nodes from the PHYP and ends up renaming
>> the new properties e.g.
>>
>> [ 4565.827296] Duplicate name in base, renamed to "ibm,platform-facilities#1"
>>
>> There is no check like 'of_node_check_flag(np, OF_DETACHED)' within
>> of_find_node_by_phandle to skip nodes that are detached, but still
>> present due to caching or use count considerations.  Also, note that
>> of_find_node_by_phandle also uses a 'phandle_cache' which does not
>> appear to be updated when of_detach_node() is invoked.
> 
> This seems like the real bug. Since the phandle cache was added we can
> now find detached nodes when we shouldn't be able to.
> 
> Does the patch below work?
> 
> cheers
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 09692c9b32a7..d8e4534c0686 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -1190,6 +1190,10 @@ struct device_node *of_find_node_by_phandle(phandle handle)
>  		if (phandle_cache[masked_handle] &&
>  		    handle == phandle_cache[masked_handle]->phandle)
>  			np = phandle_cache[masked_handle];
> +
> +		/* If we find a detached node, remove it */
> +		if (of_node_check_flag(np, OF_DETACHED))
> +			np = phandle_cache[masked_handle] = NULL;
>  	}
> 
>  	if (!np) {
> 
> 

-- 
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line  363-5196
External: (512) 286-5196
Cell:       (512) 466-0650
mwb@xxxxxxxxxxxxxxxxxx