Re: [PATCH] powerpc: ptrace: tm_reclaim_current() in flush_tmregs_to_thread()

[Michael Ellerman <mpe@ellerman.id.au>]

Cyril Bur <cyrilbur@gmail.com> writes:

> There was an assumption that flush_tmregs_to_thread() would only be
> called for a task which is not current. And a warning could be shown
> to indicate that current is being ptraced.
>
> In the event of a core dump the current threads state is needed. This
> means that flush_tmregs_to_thread() must do its best to flush even for
> current.
>
> This patch also moves flush_tmregs_to_thread() into ptrace.c as it is
> only called from that file.
>
> Signed-off-by: Cyril Bur <cyrilbur@gmail.com>

I munged the change log a bunch:

  powerpc/ptrace: Fix coredump since ptrace TM changes
  
  Commit 8d460f6156cd ("powerpc/process: Add the function
  flush_tmregs_to_thread") added flush_tmregs_to_thread() and included
  the assumption that it would only be called for a task which is not
  current.
  
  Although this is correct for ptrace, when generating a core dump, some
  of the routines which call flush_tmregs_to_thread() are called. This
  leads to a WARNing such as:
  
    Not expecting ptrace on self: TM regs may be incorrect
    ------------[ cut here ]------------
    WARNING: CPU: 123 PID: 7727 at arch/powerpc/kernel/process.c:1088 flush_tmregs_to_thread+0x78/0x80
    CPU: 123 PID: 7727 Comm: libvirtd Not tainted 4.8.0-rc1-gcc6x-g61e8a0d #1
    task: c000000fe631b600 task.stack: c000000fe63b0000
    NIP: c00000000001a1a8 LR: c00000000001a1a4 CTR: c000000000717780
    REGS: c000000fe63b3420 TRAP: 0700   Not tainted  (4.8.0-rc1-gcc6x-g61e8a0d)
    MSR: 900000010282b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]>  CR: 28004222  XER: 20000000
    ...
    NIP [c00000000001a1a8] flush_tmregs_to_thread+0x78/0x80
    LR [c00000000001a1a4] flush_tmregs_to_thread+0x74/0x80
    Call Trace:
     flush_tmregs_to_thread+0x74/0x80 (unreliable)
     vsr_get+0x64/0x1a0
     elf_core_dump+0x604/0x1430
     do_coredump+0x5fc/0x1200
     get_signal+0x398/0x740
     do_signal+0x54/0x2b0
     do_notify_resume+0x98/0xb0
     ret_from_except_lite+0x70/0x74
  
  So fix flush_tmregs_to_thread() to detect the case where it is called on
  current, and a transaction is active, and in that case flush the TM regs
  to the thread_struct.
  
  This patch also moves flush_tmregs_to_thread() into ptrace.c as it is
  only called from that file.
  
  Fixes: 8d460f6156cd ("powerpc/process: Add the function flush_tmregs_to_thread")
  Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
  [mpe: Flesh out change log]
  Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>


cheers