On 09/22, Naveen N. Rao wrote:
>
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1751,6 +1751,19 @@ static struct uprobe *find_active_uprobe(unsigned long
> bp_vaddr, int *is_swbp)
> uprobe = find_uprobe(inode, offset);
> }
>
> + /* Ensure that the breakpoint was actually installed */
> + if (uprobe) {
> + /*
> + * TODO: move copy_insn/etc into _register and remove
> + * this hack. After we hit the bp, _unregister +
> + * _register can install the new and not-yet-analyzed
> + * uprobe at the same address, restart.
> + */
> + smp_rmb(); /* pairs with wmb() in prepare_uprobe() */
> + if (unlikely(!test_bit(UPROBE_COPY_INSN,
> &uprobe->flags)))
> + uprobe = NULL;
> + }
ACK ...
but the comment is no longer valid, it only mentions the race unregister +
register.
And note that "restart" is not true in that we are not going to simply restart,
we will check is_trap_at_addr() and then either send SIGTRAP or restart.
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.
And btw, perhaps you should do this check right after find_uprobe() in the
if (valid_vma) block.
Oleg.
