On Mon, Mar 1, 2021 at 5:36 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote: > On Sun, Feb 28, 2021 at 8:21 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote: > > On Fri, Feb 26, 2021 at 6:12 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote: > > > On Fri, Feb 26, 2021 at 2:07 AM Paul Moore <paul@xxxxxxxxxxxxxx> wrote: > > > > On Wed, Feb 24, 2021 at 4:35 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote: ... > > Ah, yes, you're right. I was only thinking about the problem of > > adding an entry to the old sidtab, and not the (much more likely case) > > of an entry being added to the new sidtab. Bummer. > > > > Thinking aloud for a moment - what if we simply refused to add new > > sidtab entries if the task's sidtab pointer is "old"? Common sense > > would tell us that this scenario should be very rare at present, and I > > believe the testing mentioned in this thread adds some weight to that > > claim. After all, this only affects tasks which entered into their > > RCU protected session prior to the policy load RCU sync *AND* are > > attempting to add a new entry to the sidtab. That *has* to be a > > really low percentage, especially on a system that has been up and > > running for some time. My gut feeling is this should be safe as well; > > all of the calling code should have the necessary error handling in > > place as there are plenty of reasons why we could normally fail to add > > an entry to the sidtab; memory allocation failures being the most > > obvious failure point I would suspect. This obvious downside to such > > an approach is that those operations which do meet this criteria would > > fail - and we should likely emit an error in this case - but is this > > failure really worse than any other transient kernel failure, > > No, I don't like this approach at all. Before the sidtab refactor, it > had been done exactly this way ... I recognize I probably haven't made my feelings about reverts clear, or if I have, I haven't done so recently. Let me fix that now: I *hate* them. Further I hate reverts with a deep, passionate hatred that I reserve for very few things. Maybe we have to revert this change, even though I *hate* reverts they do remain an option; you just need to be 99% sure you've exhausted all the other options first. > Perhaps it wasn't clear from what I wrote, but I certainly don't want > to abandon it completely. Just to revert to a safe state until we > figure out how to do the RCU policy reload safely. The solution with > two-way conversion seems doable, it's just not a quick and easy fix. I suggest pursuing this before the revert to see what it looks like and we can discuss it further during review. -- paul moore www.paul-moore.com
