Re: pgsql: Fix double-release of spinlock

Hi,

On 2024-07-29 11:31:56 -0400, Tom Lane wrote:
> Heikki Linnakangas <heikki.linnakangas@iki.fi> writes:
> > Commit 9d9b9d46f3 added spinlocks to protect the fields in ProcSignal
> > flags, but in EmitProcSignalBarrier(), the spinlock was released
> > twice. With most spinlock implementations, releasing a lock that's not
> > held is not easy to notice, because most of the time it does nothing,
> > but if the spinlock was concurrently acquired by another process, it
> > could lead to more serious issues. Fortunately, with the
> > --disable-spinlocks emulation implementation, it caused more visible
> > failures.
> 
> There was some recent discussion about getting rid of
> --disable-spinlocks on the grounds that nobody would use
> hardware that lacked native spinlocks.  But now I wonder
> if there is a testing/debugging reason to keep it.

Seems it'd be a lot more straightforward to just add an assertion to the
x86-64 spinlock implementation verifying that the spinlock isn't already free?

Greetings,

Andres Freund