Re: [Xen-devel] [PATCH] xenbus: don't BUG() on user mode induced condition

[Sylvain Munaut <s.munaut@xxxxxxxxxxxxxxxxxxxx>]

Hi,

>> I'm trying to find out why just doing "xenstore-ls" doesn't work on my
>> 4.4.20 kernel and when stracing it, I see it doing :
>
> That looks like the same brokeness I reported earlier:
> https://lists.xenproject.org/archives/html/xen-devel/2016-08/msg02496.html
> Luckily I'm not alone with that :)

Yes indeed, looks like the same root cause, although my symptoms were
a bit different.
I had googled around a bit before posting but didn't find you post, I
guess my google-fu failed me.

As for the fix, I went with the patch below ... no idea if it's really
correct, but it seemed right to me.
Hopfully someone more knowledgeable will come up with the right fix.


diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c
b/drivers/xen/xenbus/xenbus_dev_frontend.c
index 531e764..a60eec6 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -316,7 +316,7 @@ static int xenbus_write_transaction(unsigned msg_type,
                        rc = -ENOMEM;
                        goto out;
                }
-       } else {
+       } else if (u->u.msg.tx_id || msg_type == XS_TRANSACTION_END) {
                list_for_each_entry(trans, &u->transactions, list)
                        if (trans->handle.id == u->u.msg.tx_id)
                                break;


Cheers,

    Sylvain

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