Commit f144e7c7 authored Mar 10, 2007 by Mathieu Desnoyers Committed by Paul Mackerras Mar 16, 2007

[POWERPC] Fix atomicity of TIF update in flush_thread()



Fix atomicity of TIF update in flush_thread() for powerpc

Fixes it correctly with *_ti_thread_flag.

Race :

parent process executing :
sys_ptrace()
 (lock_kernel())
 (ptrace_get_task_struct(pid))
 arch_ptrace()
   ptrace_detach()
     ptrace_disable(child);
       clear_singlestep(child);
         clear_tsk_thread_flag(child, TIF_SINGLESTEP);
         (which clears the TIF_SINGLESTEP flag atomically from a different
          process)
 (put_task_struct(child))
 (unlock_kernel())

And at the same time, in the child process :
sys_execve()
 do_execve()
   search_binary_handler()
     load_elf_binary()
       flush_old_exec()
         flush_thread()
           doing a non-atomic thread flag update

Applies on 2.6.20.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Paul Mackerras <paulus@samba.org>

parent db98e0b4

arch/powerpc/kernel/process.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -465,8 +465,13 @@ void flush_thread(void)
		#ifdef CONFIG_PPC64
		struct thread_info *t = current_thread_info();

		if (t->flags & _TIF_ABI_PENDING)
		t->flags ^= (_TIF_ABI_PENDING \| _TIF_32BIT);
		if (test_ti_thread_flag(t, TIF_ABI_PENDING)) {
		clear_ti_thread_flag(t, TIF_ABI_PENDING);
		if (test_ti_thread_flag(t, TIF_32BIT))
		clear_ti_thread_flag(t, TIF_32BIT);
		else
		set_ti_thread_flag(t, TIF_32BIT);
		}
		#endif

		discard_lazy_cpu_state();