Messages in this thread | | | Date | Fri, 29 Sep 2017 18:54:25 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v3 3/3] kernel/uprobes: Fix check for active uprobe |
| |
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.
| |