Messages in this thread | | | Date | Thu, 26 Mar 2020 13:57:30 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH v3] driver core: Break infinite loop when deferred probe can't be satisfied |
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On Thu, Mar 26, 2020 at 09:39:40AM +0100, Rafael J. Wysocki wrote: > On Wed, Mar 25, 2020 at 11:09 PM Saravana Kannan <saravanak@google.com> wrote: > > On Wed, Mar 25, 2020 at 5:51 AM Andy Shevchenko > > <andriy.shevchenko@linux.intel.com> wrote:
> > > Yes, it's (unlikely) possible (*), but it will give one more iteration per such > > > case. It's definitely better than infinite loop. Do you agree? > > > > Sorry I wasn't being clear (I was in a rush). I'm saying this patch > > can reintroduce the bug where the deferred probe isn't triggered when > > it should be. > > > > Let's take a simple execution flow. > > > > probe_okay is at 10. > > > > Thread-A > > really_probe(Device-A) > > local_probe_okay_count = 10 > > Device-A probe function is running... > > > > Thread-B > > really_probe(Device-B) > > Device-B probes successfully. > > probe_okay incremented to 11 > > > > Thread-C > > Device-C (which had bound earlier) is unbound (say module is > > unloaded or a million other reasons). > > probe_okay is decremented to 10. > > > > Thread-A continues > > Device-A probe function returns -EPROBE_DEFER > > driver_deferred_probe_add_trigger() doesn't do anything because > > local_probe_okay_count == probe_okay > > But Device-A might have deferred probe waiting on Device-B. > > Device-A never probes. > > > > > *) It means during probe you have _intensive_ removing, of course you may keep > > > kernel busy with iterations, but it has no practical sense. DoS attacks more > > > effective in different ways. > > > > I wasn't worried about DoS attacks. More of a functional correctness > > issue what I explained above. > > The code is functionally incorrect as is already AFAICS. > > > Anyway, if your issue and similar issues can be handles in driver core > > in a clean way without breaking other cases, I don't have any problem > > with that. Just that, I think the current solution breaks other cases. > > OK, so the situation right now is that commit 58b116bce136 has > introduced a regression and so it needs to be fixed or reverted. The > cases that were previously broken and were unbroken by that commit > don't matter here, so you cannot argue that they would be "broken". > > It looks to me like the original issue fixed by the commit in question > needs to be addressed differently, so I would vote for reverting it > and starting over.
I think Saravana's example is not fully correct as I had responded to his mail. I would like to hear Grant, but seems he is busy with something and didn't reply.
> > As an alternate solution, assuming "linux,extcon-name" is coming > > from some firmware, you might want to look into the fw_devlink > > feature. > > That would be a workaround for a driver core issue, though, wouldn't it?
As I explained to him, this issue is not limited to USB case.
-- With Best Regards, Andy Shevchenko
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