On 11/26/2015 06:07 AM, Seymour, Shane M wrote: > Hi Hannes, > > I have one probably small nitpick about the patch. I'm not sure how likely what I've put below is likely > to happen in real life though. > > Is there any chance at all that sdev->vpd_pg83_len could change when updated? > If there's any chance of that I'd have expected that both the length of and the pointer to the vpd data > would need to be protected not just the pointer so someone would have a consistent picture of the vpd > and its length. Without that there is a race where someone could be using a new length with the old vpd > data. That leaves the potential for a length that exceeds the vpd size if the new data is larger than > the old data - I don't know how likely it is but wanted to at least bring it up as something to consider. > Accesses to vpd_pgXX are rcu-protected, so we're ensured that we always see a _valid_ copy. And we know that integer updates are atomic, so we will always see a valid number in vpd_pgXX_len. Both, vpd_pgXX and vpd_pgXX_len, are updated at the same place, and under the same locks/mutexes. And as we're calling 'synchronize_rcu()' after updating vpd_pgXX, which needs to synchronize against all CPUs, I would think that this would take care of updating vpd_pgXX_len, too. But you are right, we can get rid of vpd_pgXX_len and calculate it from the data. However, I'd like to do this with another patch after the ALUA changes are in. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
