Re: PCIe enable device races (Was: [PATCH v3] PCI: Data corruption happening due to race condition)

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2018-08-16 at 14:52 +0530, Hari Vyas wrote:
> 
> There was an issue reported by my colleague srinath while enabling pci
> bridge and a race
> condition was happening while setting memory and master bits i.e. bits
> were over-written.
> As per my understanding is_busmaster and is_added bit race issue was
> at internal data
> management and is quite different from pci bridge enabling issue.
> Am I missing some thing ? Would be interested to know what exactly was
> affected due to
> is_busmaster fix.

The is_busmaster fix isn't I think affecting anything, however I don't
like the use of atomics for these things. It's a band-aid. If we grow a
proper pci_dev mutex, which is what I'm introducing here, it should be
able to also handle the is_added race etc..

> In any case, one bug is already filed and may propose a patch soon
> about pci bridge enabling scenario.

I already did, see the patch I posted earlier.

>  In summary, bit manipulation is not working fine due to race
> conditions in SMP
> environment.

Right, among other things.

My proposed patch (which I will try to break down tomorrow or next week
into smaller bits) introduces a per-pci_dev mutex and uses it to fix
the enable & set_master races.

My proposal is to then progressively move more things under the
umbrella of that mutex in order to properly protect the pci_dev
internal state.

Cheers,
Ben.

> Regards,
> hari