On 22/08/2016 09:32, Cyril Bur wrote: > Userspace can begin and suspend a transaction within the signal > handler which means they might enter sys_rt_sigreturn() with the > processor in suspended state. > > sys_rt_sigreturn() wants to restore process context (which may have > been in a transaction before signal delivery). To do this it must > restore TM SPRS. To achieve this, any transaction initiated within the > signal frame must be discarded in order to be able to restore TM SPRs > as TM SPRs can only be manipulated non-transactionally.. > From the PowerPC ISA: > TM Bad Thing Exception [Category: Transactional Memory] > An attempt is made to execute a mtspr targeting a TM register in > other than Non-transactional state. > > Not doing so results in a TM Bad Thing: > [12045.221359] Kernel BUG at c000000000050a40 [verbose debug info unavailable] > [12045.221470] Unexpected TM Bad Thing exception at c000000000050a40 (msr > 0x201033) > [12045.221540] Oops: Unrecoverable exception, sig: 6 [#1] > [12045.221586] SMP NR_CPUS=2048 NUMA PowerNV > [12045.221634] Modules linked in: xt_CHECKSUM iptable_mangle ipt_MASQUERADE > nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 > nf_defrag_ipv4 > xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 xt_tcpudp bridge stp llc > ebtable_filter > ebtables ip6table_filter ip6_tables iptable_filter ip_tables x_tables kvm_hv > kvm > uio_pdrv_genirq ipmi_powernv uio powernv_rng ipmi_msghandler autofs4 ses > enclosure > scsi_transport_sas bnx2x ipr mdio libcrc32c > [12045.222167] CPU: 68 PID: 6178 Comm: sigreturnpanic Not tainted 4.7.0 #34 > [12045.222224] task: c0000000fce38600 ti: c0000000fceb4000 task.ti: > c0000000fceb4000 > [12045.222293] NIP: c000000000050a40 LR: c0000000000163bc CTR: > 0000000000000000 > [12045.222361] REGS: c0000000fceb7ac0 TRAP: 0700 Not tainted (4.7.0) > [12045.222418] MSR: 9000000300201033 <SF,HV,ME,IR,DR,RI,LE,TM[SE]> CR: > 28444280 XER: 20000000 > [12045.222625] CFAR: c0000000000163b8 SOFTE: 0 PACATMSCRATCH: 900000014280f033 > GPR00: 01100000b8000001 c0000000fceb7d40 c00000000139c100 c0000000fce390d0 > GPR04: 900000034280f033 0000000000000000 0000000000000000 0000000000000000 > GPR08: 0000000000000000 b000000000001033 0000000000000001 0000000000000000 > GPR12: 0000000000000000 c000000002926400 0000000000000000 0000000000000000 > GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > GPR24: 0000000000000000 00003ffff98cadd0 00003ffff98cb470 0000000000000000 > GPR28: 900000034280f033 c0000000fceb7ea0 0000000000000001 c0000000fce390d0 > [12045.223535] NIP [c000000000050a40] tm_restore_sprs+0xc/0x1c > [12045.223584] LR [c0000000000163bc] tm_recheckpoint+0x5c/0xa0 > [12045.223630] Call Trace: > [12045.223655] [c0000000fceb7d80] [c000000000026e74] > sys_rt_sigreturn+0x494/0x6c0 > [12045.223738] [c0000000fceb7e30] [c0000000000092e0] system_call+0x38/0x108 > [12045.223806] Instruction dump: > [12045.223841] 7c800164 4e800020 7c0022a6 f80304a8 7c0222a6 f80304b0 7c0122a6 > f80304b8 > [12045.223955] 4e800020 e80304a8 7c0023a6 e80304b0 <7c0223a6> e80304b8 > 7c0123a6 4e800020 > [12045.224074] ---[ end trace cb8002ee240bae76 ]--- > > It isn't clear exactly if there is really a use case for userspace > returning with a suspended transaction, however, doing so doesn't (on > its own) constitute a bad frame. As such, this patch simply discards > the transactional state of the context calling the sigreturn and > continues. > > Reported-by: Laurent Dufour <lduf...@linux.vnet.ibm.com> > Signed-off-by: Cyril Bur <cyril...@gmail.com> > --- > V2: Move the code down into the #ifdef CONFIG_PPC_TRANSACTIONAL_MEM (32 and > 64 bit) > Add a small amount of text to Documentation > Adjust the commit message for clarity >
FWIW, Tested-by: Laurent Dufour <lduf...@linux.vnet.ibm.com>
