On Tue, Feb 3, 2026 at 6:26 PM Andres Freund <[email protected]> wrote: > > While looking at converting more places to UnlockReleaseBuffer(), in the > course of making UnlockReleaseBuffer() faster than the two separate > operations, I found this code: > > static bool > ginScanToDelete(GinVacuumState *gvs, BlockNumber blkno, bool isRoot, > DataPageDeleteStack *parent, OffsetNumber > myoff) > ... > > if (!meDelete) > { > if (BufferIsValid(me->leftBuffer)) > UnlockReleaseBuffer(me->leftBuffer); > me->leftBuffer = buffer; > } > else > { > if (!isRoot) > LockBuffer(buffer, GIN_UNLOCK); > > ReleaseBuffer(buffer); > } > > if (isRoot) > ReleaseBuffer(buffer); > > > Which sure looks like it'd release buffer twice if isRoot is set? I guess > that's not reachable, because presumably the root page will always go down the > !meDelete path. But it sure made me wonder if there's a hard to reach bug.
Yes, it's not possible to have meDelete set for root, because me->leftBuffer is always InvalidBuffer for the root. So the branch handling meDelete case should better do Assert(!isRoot). > This code was introduced in > commit e14641197a5 > Author: Alexander Korotkov <[email protected]> > Date: 2019-11-19 23:07:36 +0300 > > Fix deadlock between ginDeletePage() and ginStepRight() > > I didn't trace it further to see if it existed before that in some fashion. Yes. I think generally this area needs to be reworked to become more clear, and have vast more comments. It was wrong from my side trying to fix bugs there without reworking it into something more appropriate. I'm planning to put work on this during this week. > There's another oddity here: ginScanToDelete() requires that the root page has > been locked by the caller already, but will afaict re-read the root page? But > then have code to avoid locking it again, because that would not have worked? > Seems odd. It seems a bit odd for me that caller already have locked buffer, but passes BlockNumber making us re-read the buffer. But I'm not sure that's the same as your point. Could you, please, elaborate more on this? ------ Regards, Alexander Korotkov Supabase
