Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=f144e7c7272bf527c380bffaa5e789dc28a09d8d
Commit:     f144e7c7272bf527c380bffaa5e789dc28a09d8d
Parent:     db98e0b434a6265c451ffe94ec0a29b8d0aaf587
Author:     Mathieu Desnoyers <[EMAIL PROTECTED]>
AuthorDate: Sat Mar 10 03:23:03 2007 -0500
Committer:  Paul Mackerras <[EMAIL PROTECTED]>
CommitDate: Fri Mar 16 16:37:28 2007 +1100

    [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 <[EMAIL PROTECTED]>
    Signed-off-by: Paul Mackerras <[EMAIL PROTECTED]>
---
 arch/powerpc/kernel/process.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index f3d4dd5..e53b298 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -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();
-
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