Messages in this thread | ![/](/images/icornerl.gif) | | Date | Fri, 23 Nov 2018 08:34:02 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] uprobes: Fix handle_swbp() vs. unregister() + register() race once more |
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* Oleg Nesterov <oleg@redhat.com> wrote:
> On 11/22, Oleg Nesterov wrote: > > On 11/22, Andrea Parri wrote: > > > > > > Commit 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + > > > register() race") added the UPROBE_COPY_INSN flag, and corresponding > > > smp_wmb() and smp_rmb() memory barriers, to ensure that handle_swbp() > > > uses fully-initialized uprobes only. > > > > > > However, the smp_rmb() is mis-placed: this barrier should be placed > > > after handle_swbp() has tested for the flag, thus guaranteeing that > > > (program-order) subsequent loads from the uprobe can see the initial > > > stores performed by prepare_uprobe(). > > > > > > Move the smp_rmb() accordingly. Also amend the comments associated > > > to the two memory barriers to indicate their actual locations. > > > > > > Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com> > > > Cc: Peter Zijlstra <peterz@infradead.org> > > > Cc: Ingo Molnar <mingo@redhat.com> > > > Cc: Arnaldo Carvalho de Melo <acme@kernel.org> > > > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > > > Cc: Jiri Olsa <jolsa@redhat.com> > > > Cc: Namhyung Kim <namhyung@kernel.org> > > > Cc: Oleg Nesterov <oleg@redhat.com> > > > Cc: stable@kernel.org > > > Fixes: 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + register() race") > > > > Thanks, > > > > Acked-by: Oleg Nesterov <oleg@redhat.com> > > Yes, but I am not sure this is the -stable material...
So I left the Cc: stable tag intact, because this is a really low-risk fix (it just moves barriers around), and clearly fixes a bug that people might or might not have observed.
Even if they observed it the race is probably very hard to reproduce and almost impossible to report - so we are better off propagating this fix to -stable, as there's no realistic actionable way for users to actually complain about the bug if it affects them.
That's the general backporting policy for race fixes, unless they are really, really intrusive - which this one isn't really.
Thanks,
Ingo
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