Re: [xen-devel][PATCH] concurrency control issues in netback

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 5 Jun 2006, at 04:18, Ky Srinivasan wrote:

> I have been looking at the netback code (netback.c) and I think there
> may be a bug in the way concurrency is managed here. Specifically, the
> function that cleans up completed requests (net_tx_action_dealloc()) is
> executed only from within a tasklet and hence does not acquire any 
> locks
> to manipulate global state that could potentially be modified from 
> other
> cpus. The code seems to assume writes are ordered without explicitly
> forcing the ordering. The problematic  global state is the index that
> keeps track of the last valid index to be dealloced (dealloc_prod). 
> This
>  could potentially be manipulated outside of the tasklet.
That's a good catch! Does your patch fix the network problems that you 
guys have been seeing?
The patch needs cleaning up: at least to rename the lock, but actually 
just explicitly forcing the ordering we need is probably better. I'll 
sort that out and check in a suitable fix.
 Thanks!
 Keir


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