On 09/29, Srikar Dronamraju wrote: > > > This is correct because we do this check under mmap_sem so we can't race > > with > > install_breakpoint(), so is_trap_at_addr() == T can't be falsely true if > > UPROBE_COPY_INSN is not set. > > > > Right, Given that we are doing this in the mmap_sem, we should also be > removing the rmb/wmb pairs too.
Well, down_read(&mm->mmap_sem) can only guarantee that this mm can not be modified by install_breakpoint(). But what if, say, another task with different ->mm does uprobe_mmap() and calls prepare_uprobe() for the 1st time? Or suppose we race with unregister+register... OTOH, I agree that we can remove these barriers, but this needs a lengthy comment while the current code looks "obviously correct" in that you do not even need to think about potential races. Oleg.
