Hi Michael Bringmann, On 12/11/18 8:07 AM, Rob Herring wrote: > On Tue, Dec 11, 2018 at 7:29 AM Michael Ellerman <mpe@xxxxxxxxxxxxxx> 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 >> >> 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; The bug you found exposes a couple of different issues, a little bit deeper than the proposed fix. I'll work on a fuller fix tonight or tomorrow. > I'm wondering if we should explicitly remove the node from the cache > when we set OF_DETACHED. Otherwise, it could be possible that the node > pointer has been freed already. Or maybe we need both? Yes, it should be explicitly removed. I may also add in a paranoia check in of_find_node_by_phandle(). -Frank > > Rob >
