On Mon, Sep 10, 2012 at 08:47:53AM +0800, Fengguang Wu wrote: > Al, > > Something bad happens since the below commit. Because commit [12/18] f411932 > was not tested, it might also be the first bad commit.
There's a damn good reason why the branch is called the way it's called ;-) It's missing a lot of kernel_thread() stuff; I'm still not sure if it's worth going that way, but there are some very attractive aspects. Basically, if we had guaranteed that pt_regs instance on the bottom of the stack will _not_ overlap anything for a kernel thread, we can move copying pt_regs into kernel_execve() itself. Which simplifies the hell out of ret_from_kernel_execve() instances... The price is that we need to leave that space aside for kernel threads. It's not _that_ much and kernel threads are generally less stack-hungry than the worst cases of syscalls (note that for userland process in the middle of syscall that pt_regs instance *will* be there, no matter what). FWIW, the plan for that branch is to do the following trick: either split ret_from_kernel_thread away from ret_from_fork, setting the right one to be used at copy_thread() time or make ret_from_fork itself check if it's returning to kernel. Either way, do *not* go through return from syscall in return to kernel case; instead of that, have ret_from_kernel_thread: schedule_tail(); get the function to be called and its argument from regs and call it pass return value to do_exit() (BTW, I'm not at all sure we wouldn't be better off if we took those do_exit() calls into 3--5 places in callbacks; kernel_thread() is really very low-level and has few immediate callers). Of course, such patches would have to go before the ret_from_kernel_execve() ones. Right now this branch is guaranteed to be broken; build testing does make sense, but trying to boot it... Not yet. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/