From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Sat, 10 Mar 2007 08:23:03 +0000 (-0500)
Subject: [POWERPC] Fix atomicity of TIF update in flush_thread()
X-Git-Tag: v2.6.21-rc5~31^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f144e7c7272bf527c380bffaa5e789dc28a09d8d;p=pandora-kernel.git

[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>
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