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Date: Thu, 8 Mar 2007 21:45:25 -0500 From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> To: akpm@...ux-foundation.org, mbligh@...gle.com, linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org, paulus@...ba.org Subject: [PATCH] Fix atomicity of TIF update in flush_thread() for powerpc Fix atomicity of TIF update in flush_thread() for powerpc 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@...ymtl.ca> --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -476,8 +476,13 @@ 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_tsk_thread_flag(tsk, TIF_ABI_PENDING)) { + clear_tsk_thread_flag(tsk, TIF_ABI_PENDING); + if (test_tsk_thread_flag(tsk, TIF_32BIT)) + clear_tsk_thread_flag(tsk, TIF_32BIT); + else + set_tsk_thread_flag(tsk, TIF_32BIT); + } #endif discard_lazy_cpu_state(); -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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